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SPECIAL ARTICLE |
a New England Newborn Screening Program and Department of Pediatrics, University of Massachusetts Medical School, Worcester, Massachusetts
b Department of Pediatrics, Mike McMorris Cystic Fibrosis Research and Treatment Center, University of Colorado Health Sciences Center and Children's Hospital, Denver, Colorado
c Cystic Fibrosis Foundation, Bethesda, Maryland
d State Laboratory of Hygiene
l Department of Pediatrics, University of Wisconsin, Madison, Wisconsin
e Department of Newborn Medicine, Brigham and Women's Hospital, Boston, Massachusetts
f Department of Newborn Medicine, Children's Hospital, Boston, Massachusetts
g Social and Behavioral Research Branch, National Human Genome Research Institute
h Department of Clinical Bioethics, Warren G. Magnuson Clinical Center, National Institutes of Health, Bethesda, Maryland
i Department of Pediatrics, University of Washington School of Medicine, Seattle, Washington
j Department of Preventive Medicine, University of Colorado Health Sciences Center, Denver, Colorado
k Department of Respiratory Medicine, Royal Children's Hospital, Melbourne, Australia
m Department of Pediatrics, University of Massachusetts Medical Center, Worcester, Massachusetts
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ABSTRACT |
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 TOP ABSTRACT SYSTEMATIC PLANNING FOR CF...SPECIFICATIONS FOR SUCCESSFUL CF...REFERENCES |
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Key Words: newborn screening • cystic fibrosis • genotype • sweat test • guidelines
Abbreviations: CF—cystic fibrosis • NBS—newborn screening • PCP—primary care provider • MI—meconium ileus • IRT—immunoreactive trypsinogen • CFTR—Cystic Fibrosis Transmembrane Conductance Regulator • CLSI—Clinical and Laboratory Standards Institute • QNS—quantity not sufficient • Cl–—chloride
Cystic fibrosis (CF) is one of the most common life-shortening genetic diseases in the United States, affecting 
30000 children and young adults. Because early treatment improves outcome1–15 and the Centers for Disease Control and Prevention has stated that the addition of CF to state newborn screening (NBS) programs is justified,16 there has been increased interest in adding CF to state NBS programs. Individuals who are diagnosed with CF through NBS have improved nutritional status,17 better growth,14 and fewer hospitalizations,17–19 whereas a delayed diagnosis can result in significant cognitive dysfunction20 and nutritional failure.4 NBS has been shown to decrease the risk of life-threatening complications21 or death21,22 from CF in infancy or early childhood. Families of those with CF also benefit substantially from CF NBS, because they avoid the average 15-month delay between onset of symptoms and diagnosis17 along with the accompanying anxiety, frustration, and emotional distress.23 Costs of diagnosis, and possibly treatment (through fewer hospitalizations), are reduced by NBS.24 Finally, families can benefit from genetic counseling and identification of CF in older siblings as a result of NBS discovery of CF mutations.
Although CF NBS offers tremendous benefits for individuals diagnosed with CF and their families, it is accompanied by risks that also must be considered for optimal NBS-program design. These risks include the potential that infants with CF could have a delayed diagnosis by primary care providers (PCPs) who believe a negative NBS result is definitive,25 and that infants who are properly identified with CF by the screen could be exposed to health care–acquired infections during the diagnostic evaluation or early treatment.23 The families of infants with a positive screening result but not CF could experience unnecessary anxiety before the diagnostic result,26,27 and doubts regarding the health of their normal infant may persist even afterward.28–31 Recognition of these risks is vital for optimal NBS-program design.
Components of a well-designed system necessary to address these issues successfully, as determined at a workshop held by the CF Foundation and attended by representatives from numerous state and international NBS programs, government agencies, and CF Foundation–accredited care centers (see "Acknowledgments"), are described here. The CF Foundation recommends implementation of CF screening in all newborns, with appropriate attention to these guidelines to reduce risks and maximize benefits for all participants
The goal of CF NBS programs should be to provide infants with CF an early opportunity to receive specialized medical care that will assist them in maintaining normal growth and development and delay pulmonary infection, with its associated subsequent decline of lung function. To that end, CF NBS programs should be integrated within established systems such as state-based NBS programs to assure comprehensive education, testing, tracking, follow-up, and outcomes assessments. These NBS programs provide opportunity for early identification and treatment of infants who have disorders that otherwise would go unrecognized before irreversible clinical damage. This early opportunity is possible because indicators of disorders are detectable in the dried blood spot specimens that are collected universally from the newborn population at 2 days of age during a presymptomatic period. NBS as a successful population-based public health service began in the early 1960s when statewide screening for phenylketonuria was first implemented.32 Since that time, it has become a service offered by all states and most industrialized nations and includes screening for a variety of disorders.
NBS programs support sophisticated systems for coordination of their educational, laboratory, communications, and clinical services (ref 33 and Table 1). The particular disorders that are screened by each state's program are determined by state authority (state lists are available at http://genes-r-us.uthscsa.edu/nbsdisorders.htm). NBS programs can and do add new disorders, some of which are universally required and some of which are optional. The determination of whether CF is included in a state's NBS panel and, if so, whether it is included as a required (mandatory) or optional screen is in the purview of the state authority.
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SYSTEMATIC PLANNING FOR CF NBS |
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TOPABSTRACTSYSTEMATIC PLANNING FOR CF...SPECIFICATIONS FOR SUCCESSFUL CF...REFERENCES |
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Finally, the CF NBS workgroup should ensure that all necessary guidelines for systems and care are in place before CF NBS implementation. A manuscript detailing the protocol for care of the newborn diagnosed with CF through NBS is under preparation by the CF Foundation.
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SPECIFICATIONS FOR SUCCESSFUL CF NBS PROGRAMS |
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TOPABSTRACTSYSTEMATIC PLANNING FOR CF...SPECIFICATIONS FOR SUCCESSFUL CF...REFERENCES |
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IRT Analysis: A Cautionary Note
Because newborns with CF and MI may have low initial IRT values,41,42 resulting in a false-negative screen, all newborns with MI should have a sweat test regardless of NBS results. In contrast, infants who have significant perinatal stress or low Apgar scores or (as observed in 1 study) are black may display high IRT values, resulting in false-positive newborn screen results.36,43 The urgency associated with the report or follow-up protocol for infants with these risk factors may need modification.
IRT/IRT Algorithms
The choice of screening algorithms will be driven partially by whether the community NBS program routinely and universally collects 2 specimens or only a single specimen. If 2 specimens are universally collected, the community has the option to assay IRT in both primary and second-tier tests on specimens collected at 2 days and then again at 14 days of age (IRT/IRT algorithm). Use of an IRT/IRT algorithm avoids the identification of large numbers of CF carriers from DNA analysis and the associated needs for genetic counseling. However, if only a single specimen is routinely collected, use of an IRT/IRT algorithm would require a specific request for a second sample and an acknowledgment that the first specimen screen result was positive. Because IRT levels decrease after the first weeks of life, the timing of sample collection is important and laboratory cutoffs for age-specific ranges must be established. In keeping with routine laboratory quality assurance, cutoff levels must be determined by each NBS laboratory to meet the desired sensitivity and specificity of the screen and should be evaluated periodically. Some laboratories may choose to use an absolute IRT value for a cutoff, whereas others may identify a percentage of the daily values as the cutoff.44 The latter method avoids the problem of seasonal variations in IRT values that may be caused by lability of the sample during shipment to the processing laboratory45 but may be more subject to variation as a result of daily population shifts.
IRT/DNA Algorithms
Some CF NBS programs may prefer to use a screen that includes DNA analysis. In fact, if the NBS program collects only a single specimen universally, then an algorithm with IRT as the primary screen followed by a DNA analysis on the specimens with elevated IRT concentrations (IRT/DNA algorithm) is typically chosen. The IRT cutoff that is selected to prompt DNA testing is a factor in producing false-positive and false-negative results that must be considered by the CF NBS workgroup.
Use of DNA analysis in the second tier of screening necessitates the selection of mutations in the CFTR gene for testing. A decision can be made to test for only the most common CFTR mutation, 
F508; for F508 and multiple mutations associated with severe disease; or for a panel of multiple mutations that includes some variants associated with mild or variable phenotypes. This decision must be based on a number of considerations, including those that are philosophical (the purpose of screening), scientific (current understanding of genotype-phenotype relationships), clinical utility (benefit to the infant and family), and practical (cost, system capacity for increased numbers of positive-screened infants).
The choice of whether to use a multiple-mutation panel or an assay for F508 alone is the first consideration. The frequency of F508 in the community will help determine the usefulness of a single-mutation assay in the second tier of the screen. In the Massachusetts CF NBS program, the use of a multiple-mutation panel (16–27 mutations) rather than just the single most common mutation increased the detection of affected infants by 50% and reduced the false-negative rate fourfold, although it also increased detection of carrier false-positive results by 43%.36 In other communities, the choice of using a single mutation in the second tier of the screen may adequately meet the needs set forth by that state's CF NBS workgroup.
The selection of mutations for a multiple-mutation panel can pose challenges, including:
T or IVS8-5T) (see the Cystic Fibrosis Mutation Database [www.genet.sickkids.on.ca/cftr]) may be associated with milder phenotypes,46 and the benefit from screening algorithms that include these mutations has not been proven. Longitudinal epidemiologic data on individuals with classes IV and V mutations are quite limited, particularly with regard to lung disease, and few studies have included enough patients with a comprehensive analysis of outcome.47 Inclusion of DNA variants with undocumented pathogenicity in NBS mutation panels risks the detection of asymptomatic infants who may have late-onset mild disease for which the clinical utility of NBS is unproven and who may also incur insurance barriers. Projections of the rates of false-negative screens should be considered in relation to the specific objectives of the CF NBS program in making a decision to exclude these mutations from a screening panel. Use of these mutations in NBS is considered in more detail in "Special Considerations" below.
Fail-safe for IRT/DNA Protocols
Some NBS programs may choose to define the presence of ultrahigh IRT levels as a positive CF NBS result regardless of DNA-analysis results. The Massachusetts NBS protocol uses ultrahigh IRT values (eg, the top 0.2% of the population values,36 recently raised to the top 0.1%) as a fail-safe protocol to identify infants with CF who have mutations that are not detected by the multiple-mutation DNA panel. To increase specificity of this fail-safe protocol, the IRT values of serial specimens are evaluated when infants have multiple samples submitted; if the value decreases to within reference levels within the first month of life, the infant is excluded from the recommendation for a sweat test.36 Because high IRT values are associated with multiple causes, some NBS programs may not consider ultrahigh IRT levels as a positive screen result.48 In California, the proposed CF NBS algorithm depends on a regionally customized DNA panel to maximize sensitivity and specificity of the newborn CF screen. In this algorithm, an IRT-level cutoff of 98.4% and at least 1 DNA mutation detected is projected to produce 661 sweat-test referrals, revealing 70 diagnosed cases of CF. Although including ultrahigh IRT levels with no DNA mutations in the positive screen results is projected to detect 2 additional infants with CF, it would also increase the number of sweat-test referrals by an additional 426 and, therefore, is not incorporated into the algorithm (M. Kharrazi, PhD, MPH, written communication, 2005). However, when the California algorithm was examined by retrospective application to the 110 CF-affected infants identified from a 4-year Massachusetts birth cohort,36 12 (11%, including 4 F508 homozygotes) would have been missed by the 98.4% IRT-level cutoff, and another 3 (3%) would have been missed by the requirement for detection of at least 1 mutation (A.M.C., unpublished data). This would have been outside the 95% detection rate that the Massachusetts program set as its goal.
Each CF NBS workgroup must decide whether the community it represents will receive more benefit from such fail-safe protocols or from protocols that require development and maintenance of population-specific mutation panels for potentially changing populations.
Summary
States that wish to start a CF NBS program may use IRT/IRT algorithms or IRT/DNA algorithms. Those adopting the latter may wish to begin developing projections of positive screen results by using the DNA-mutation frequencies identified in the CF Foundation's patient registry and then expanding the data to reflect the population subgroups in that state. Screening algorithms that include class IV and V mutations have been used in recent years, but additional data are needed to determine their appropriate role in CF NBS. As with all NBS programs, a balance must be struck between sensitivity, specificity, and clinical utility.
Postscreening Report and Education
The responsibility for finding and notifying the PCP of the infant with a positive CF screen result is typically that of the state NBS program or its associated maternal and child health bureau, although models exist in which the CF care center or the birth hospital is assigned to this role (Table 4). Because these processes can be very labor intensive, adding a large burden to the reporting system, lines of responsibility and available resources should be well defined before CF NBS implementation.
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Once the site for diagnostic testing has been identified, the follow-up person should provide detailed screening reports to the diagnostic site and the genetic counselor, if applicable. Efficient scheduling and communication with the sweat-test laboratory, genetic counselors, and clinicians will be promoted if an individual at the diagnostic center is identified to receive the CF NBS report and coordinate the follow-up evaluation.
Negative CF NBS Report
A negative result generated by a routine CF NBS may be reported in a manner that is consistent with overall NBS-program practice and in conjunction with routine reporting of other NBS tests. However, if clinical concern has prompted a request for the newborn screen result by the PCP, the CF NBS follow-up person should provide NBS results within the context of recommendations for diagnostic evaluation that are appropriate for each unique set of circumstances. Timely response to such inquiries, especially at the beginning of implementation, helps educate the medical community. Sample fact sheets to accompany the CF NBS report in response to these inquiries are provided in Appendix 3.
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Sweat-Test Laboratory Qualifications
The diagnostic quantitative pilocarpine iontophoresis sweat-chloride test should be performed according to the Clinical and Laboratory Standards Institute (CLSI, formerly the National Committee for Clinical Laboratory Standards) guidelines at a College of American Pathologists–accredited laboratory,50 as recommended by the CF Foundation. Optimally, the testing should be performed at a laboratory in affiliation with a CF Foundation–accredited care center, where the test can be coordinated with timely and appropriate genetic counseling and clinical follow-up. If the sweat-test result is positive, it is helpful for a CF clinician to be available for immediate intervention. A CF clinician can also help with interpretation of a complex diagnostic profile such as a borderline or negative sweat-test result in the presence of 2 CFTR mutations. Access to a genetic counselor and CF clinician is also helpful if there is a family history of CF, a genotype requiring literature review, or information on sensitive issues such as misattributed paternity. In addition, because infants with CF could be subjected to health care–acquired infection during their diagnostic evaluation or early treatment,23 testing and clinical care should take place at sites where this risk is recognized and rigorous CF infection-control guidelines are followed carefully.51 Ideally, the sweat test should be available within 2 to 3 hours' driving distance for the family. In regions where greater distances are unavoidable, it may be necessary to establish CLSI guideline–proficient satellite laboratories at which sweat can be both collected and tested or collected and sent to a College of American Pathologists–approved laboratory for analysis. Although not ideal (as shown in one non-US study),52,53 such arrangements could ensure acceptable testing standards and may prevent long delays in testing as well as provide a safe alternative for situations when long trips are difficult.
Minimum Age and Weight of the Infant for Valid Sweat Testing
Sweat electrolytes are high on the first day of life, but by the third day they have declined to levels seen outside the newborn period.54 The CLSI guidelines permit sweat testing after 48 hours of age. Because CF NBS results are unlikely to be available before 48 hours, the threshold for sweat testing is more likely to be related to weight rather than age; infants weighing <2 kg are more likely to provide insufficient sweat for analysis (quantity not sufficient [QNS]).
Other infants are also at increased risk for invalid test results as a result of generation of insufficient sweat. Premature infants or infants who are black exhibit a higher frequency of QNS reports.43,55,56 Newer methods of conductance determination on microsamples have been developed but are not yet adequately standardized. Because waiting for the sweat test to be performed leads to family anxiety,37 the test should be scheduled as soon as possible and parents should be informed of the risk of QNS. Sweat testing is not considered an emergency, but guidance by a CF specialist should be available for the PCP at all times.
Diagnostic Interpretation After the Sweat Test
The following guidelines are designed to help CF NBS programs develop follow-up protocols that (1) resolve the outcomes of the vast majority of infants with positive CF NBS results and (2) ensure monitoring of the small subset of infants whose diagnostic status cannot be resolved without additional guidance. A planned CF Foundation–sponsored workshop will update the published consensus case definition of CF57 and may provide assistance in addressing some of these diagnostic dilemmas. Regardless, it is most helpful to have specific diagnostic protocols developed by the state CF NBS workgroup in place before implementation so that the lines of action and responsibility are clear.
Positive Sweat-Test Result
In keeping with CLSI guidelines, sufficient quantities of sweat yielding chloride (Cl–) values of 
60 mEq/L is considered diagnostic for CF.50 Exceptions to this rule are familiar to clinicians who practice at CF care centers.58,59
Negative Sweat-Test Result
In the absence of significant clinical concern for CF, a negative sweat-test result (Cl– value of <30 mEq/L at <6 weeks of age) confirms a negative diagnosis. Clinical signs and symptoms consistent with CF or the detection of 2 pathogenic mutations in the CF newborn screen should result in reexamination of the diagnosis by a qualified CF clinician.
Borderline Sweat-Test Result
In older children and adults, a sweat Cl– value between 40 and 60 mEq/L has been termed ambiguous or "borderline" and is not clearly diagnostic. However, results from several NBS programs indicate that newborns with CF from 1 to 6 weeks of age tend to have sweat Cl– levels lower than those found in older infants and children with CF.55,60 Thus, some screening programs recommend that a lower limit of 30 mEq/L (still 5 SD above the normal mean61) be adopted as the lower limit of the borderline range in infants. In Massachusetts, lowering the cutoff from 40 to 30 mEq/L resulted in an increase from 1.1% to 3.5% in the number of screen-positive infants with a borderline sweat-test result, who then required additional monitoring before diagnostic resolution (A.M.C., unpublished data). Evaluation of any infant with a borderline sweat-test result should include repeat sweat testing scheduled for a later date. If 2 CFTR mutations were detected by the newborn screen, a CF specialist should be consulted to determine the appropriate next steps. If 1 CFTR mutation was detected by the screen, a genetic counselor should be consulted to determine if an extended panel of CFTR mutations should be used in additional testing.62
For more detailed discussion of recommendations after borderline sweat-test results, see "Diagnostic Dilemmas: Borderline Sweat-Test Results" under "Special Considerations" below.
Communicating Diagnostic-Evaluation Results to the Parents
CF NBS is optimized by effective communication of diagnostic results, including well-developed counseling and education resources.23,29,30,63–65
Positive CF Diagnosis
When the CF NBS result indicates a high likelihood of CF, the NBS program should alert the clinical care center to allow the parents to meet with a CF clinician at the time of the sweat-test visit. Ideally, the parents of any infant with a positive sweat-test result should be able to meet with a CF clinician before leaving the clinical care center. The CF clinician should be prepared to discuss the diagnosis, prognosis, immediate next steps for the parents, and a short-term plan that includes a visit to meet with the CF team, which will coordinate care with the infant's PCP. Presentation of these recommendations in writing is helpful.
In some cases, particularly at laboratories that experience a low volume of sweat testing, parents will leave before results become available. A report of the diagnosis is then made, ideally, by a CF specialist to the PCP, who will be the primary route of communication to the parents. The PCP should have adequate information (or telephone numbers of relevant CF care centers) to address initial parent concerns and should facilitate the scheduling of a follow-up appointment with the CF team. For families of infants with a positive CF diagnosis, sweat tests should be arranged for all first-degree siblings and for any half-siblings who have signs or symptoms of CF or who have 2 parents known to be carriers.
Negative CF Diagnosis
As is characteristic of all NBS, most infants with a positive CF NBS result will not have CF. Because families of infants with "false-positive" screen results (in which the screening result is positive and the diagnostic sweat test is negative) will have no continuing support from the CF care center, sympathetic and accurate transmission of information to allay future concerns takes on a high level of importance.
Insufficient Sweat for Analysis (QNS)
When a diagnosis cannot be made because of insufficient sweat collected, a person must be designated to communicate the QNS result and schedule the follow-up visit. If the parents have already been scheduled for a genetic counseling session during the same visit, the genetic counselor can help explain the report. If the parents have left the center before the QNS report or if genetic counseling was not scheduled, the PCP should be the designated liaison with the family.
Diagnostic Dilemmas
Ideally, the primary communication of an inconclusive evaluation and its meaning relative to the specific clinical situation is delivered by a CF specialist to the parents. When the PCP must deliver a complex communication, they should facilitate scheduling a follow-up with a CF specialist as indicated by the specialist; families need to be counseled about phenotypic variability associated with specific genotypes66 with relevant and accurate information about atypical or complex results.
Ambiguous diagnostic tests, discordant diagnostic tests, or inability to complete diagnostic tests heightens anxiety by prolonging the time to resolution of the positive screening result. In some instances, ambiguous diagnostic-test results may be caused by the presence of a "variant" of CF that places the family in a prolonged period of diagnostic uncertainty without a clear compensating benefit attributable to the screen or the evaluation.60,67,68 Ultimately, some of these infants may show classic signs of CF, some may never express disease, and some may develop mild phenotypes (eg, isolated congenital bilateral absence of the vas deferens) so that the interventions prompted by CF NBS might have limited clinical value. Debate continues on the appropriateness of identifying, labeling, following up, or treating infants in the absence of a clear understanding of the prognosis of their particular disorder. Information gained from ongoing experience should help improve decision-making in choosing screening algorithms that meet NBS-program goals for level of disease to be detected.
Genetic Counseling
Genetic counseling is a necessary and vital part of follow-up care for parents of children who have a CFTR mutation revealed by a positive CF NBS result. Studies have demonstrated that psychosocial sequelae of false-positive NBS results can occur, including those resulting from CF-carrier identification.69,70 Genetic counseling promotes understanding of the results and offers parents an important venue for psychosocial support and for addressing implications regarding reproductive choices for themselves and other family members.71
Some states ensure that parents of screen-positive newborns have access to genetic counseling at CF care centers on the day of the sweat test.29,30 Same-day counseling may be provided before sweat testing, while parents await results, or (optimally) after results of the sweat testing are available. However, availability and funding of genetic counseling services varies. Some CF care centers offer genetic counseling on the day of the sweat test, and others inform families that they may speak with a genetic counselor at a later date.72 (Note that genetic counselors who practice at a children's hospital should ensure that the parents' PCPs are included in decisions about any parent testing.) Scheduling the genetic counseling with the sweat test ensures transmission of information to the parents and allows knowledgeable caregivers to address the parents' immediate concerns about their child's health and begin to establish a relationship with the family of a child with a positive or borderline sweat-test result. However, trying to coordinate sweat testing together with a genetic counseling appointment may result in some delay. In addition, providing counseling on a subsequent day might result in longer-lasting understanding of the newborn screen results and family risk if the parents' acute anxiety from the sweat test has dissipated. On the other hand, offering genetic counseling on a separate day may result in a lost opportunity for counseling if parents cannot or do not return; 70% of families who were offered separate-day genetic counseling in a Massachusetts NBS program never accessed the service.73
Providers of genetic counseling related to CF NBS should have training in genetics and experience with caring for patients with CF to ensure that families receive complete care. The family's emotional needs should be addressed in a culturally sensitive manner,74 and risk assessment should include available information on families of similar ancestry.75 For example, in the families of infants who are identified as CF carriers, a parent who carries the CFTR mutation has been shown to have increased anxiety/guilt as compared with a parent who does not carry a CFTR mutation.31 It should be explained that the carrier parent's subsequent pregnancies and those of relatives are at an increased risk for CF, relative to the general population. In a small percentage of cases, both parents are carriers, although the screen-positive newborn inherited a mutation from only 1 parent. These couples have a 25% chance that a previous child has or subsequent child will have CF. Parental CF DNA analysis can be offered to identify the carrier parent and to distinguish the 1-carrier couple from the 2-carrier couple. It is important to address this issue sensitively, because parental testing can result in detection of misattributed paternity.
Several states use multiple-mutation panels, which increase the number of carriers identified by the screening process.36 The inclusion of alleles (such as R117H76 and I148T77) with inadequately understood effects necessitates detailed knowledge by the genetic counseling provider so that parents are properly informed of their child's diagnostic or carrier status and are provided with correct information regarding their chances of having a child with CF in the future.
Quality Assurance of CF NBS: Tracking and Outcomes Assessments
CF NBS is beneficial only if infants identified by the screen receive a prompt diagnostic evaluation. The responsibility for tracking the infant to assure compliance with the recommendation for evaluation and to document diagnostic outcome is typically that of the state NBS program or its associated maternal and child health bureau. To enable proper data collection and facilitate this tracking, the following must be reported to the state NBS program:
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CF care centers must be prepared to receive referrals from the screening program. Care centers and NBS-program staff should work together, therefore, to predict the number of infants who will screen positive and to outline protocols for their follow-up. In states that use IRT/DNA algorithms, the majority of screen-positive infants who do not have CF will be carriers45; before initiating screening, the number of carriers expected should be calculated to identify resources for the parents who should be offered genetic counseling as well. From these estimates, center directors can determine the resources that will be needed for sweat testing, special profile interpretation, genetic counseling, and clinical care for infants who are determined to be affected.80
Sweat-testing facilities may see a change in the number of referrals and referral patterns as a result of population-based CF NBS. In Wisconsin, the number of sweat tests ordered decreased after CF NBS implementation, presumably because of a decrease in sweat tests ordered by the PCP for CF-like symptoms; consequently, the number of facilities offering sweat testing was greatly reduced.24 In Massachusetts, the number of sweat tests increased when screening began and then diminished somewhat,81 although PCPs still order a considerable number of tests. CF care centers and NBS programs should work together to predict the number of sweat tests generated by CF NBS and decide where the tests would be performed to plan for appropriate staffing, while recognizing that sweat-test numbers may vary as the screen is implemented.
Screening algorithms designed to detect the highest number of infants with CF could overload resources available for communication, sweat testing, and counseling. Alternative screening plans may need to be considered if this results in long waits or travel times. Such alternatives might include use of mobile sweat-test laboratories that meet the same standards as those approved by the CF Foundation for standard sweat-test laboratories, quality-controlled local sweat collection that is then sent to a certified laboratory for analysis, a change in screening algorithm, or teleconference counseling.
Research Opportunities
CF NBS provides the opportunity and the responsibility to conduct research to improve treatment and outcomes in CF (Table 6). Epidemiologic/observational and therapeutic trials should be conducted. Because of the small number of infants diagnosed at each site, research projects will generally require multicenter collaboration, and some studies will require centralized coordination at the NBS-program level. NBS and early diagnosis may accelerate the adoption of new treatments for infants with CF, because it creates an opportunity to define a specific cohort from early in life for entry into clinical trials.
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CFTR Mutations and Mild Disease
The panel of CFTR mutations that the NBS program chooses for screening depends partially on the spectrum of disease that the regional program decides to detect. Because individuals with CF who have one class IV or V mutation would almost always be identified through detection of a class I, II, or III mutation on the other chromosome,87,88 some NBS programs may choose not to include class IV or V mutations in the screening panel. Indeed, removal of the class IV R117H mutation from the Massachusetts CF NBS panel would lower the false-positive rate by 10% in that population (A.M.C., unpublished results). However, the proposal to detect infants with CF with a class IV or V mutation by relying on the screen finding a class I, II, or III mutation from the other chromosome also relies on those infants having an elevated sweat Cl– level. Some individuals with class IV and V mutations can develop clinical symptoms89–93 even in the absence of an elevated sweat Cl– concentration.
Use of mutations associated with milder phenotypes may lead to results that are difficult to interpret and communicate in DNA testing of a family after positive NBS results. Because some individuals with a genotype including F508 and a class IV or V mutation may be unaffected by CF,76 testing that uses these mutations may best be limited to families of infants who are symptomatic or have a positive sweat-test result.
Complex gene modifiers associated with disease expression of the IVS8-5T mutation (eg, TG repeats and M470V polymorphism) have been identified,94,95 but the intricacy of the testing is beyond the current scope of NBS. Furthermore, although up to 20% of infants with an elevated IRT level, one F508 mutation, and a sweat Cl– level of <40 mEq/L may possess 5T on the other chromosome, none have a classic CF phenotype,96 which suggests that the IVS8-5T DNA variant, at least, should not be included in mutation panels used for CF NBS.
Diagnostic Dilemmas
Borderline Sweat-Test Results
Approximately 10% of newborns with CF that was detected through NBS using current DNA-mutation panels and diagnosed with CF by a CF clinician express sweat Cl– concentrations <60 mEq/L.28 Because sweat Cl– levels can change over time, tests resulting in a borderline result should be repeated in 1 to 2 months. In the interim, the clinician should monitor nutritional status and growth for any impact by possible pancreatic insufficiency. Also, because individuals with CF and borderline sweat-test results may be susceptible to respiratory disease regardless of pancreatic function, vigilant monitoring for respiratory problems remains critical to enable the early interventions that improve outcome.
A moderate percentage (17%) of infants with borderline sweat-test results are found to possess 2 CFTR mutations when extended mutation analysis is performed.60 Some mutations that occur in the borderline-result group, such as 3849 + 10 kb CT or A455E, are clearly associated with a disease phenotype, and infants with these mutations should be diagnosed with CF. When R117H (7T) mutation is one of the 2 CFTR mutations, diagnosis is more problematic because only some of the individuals with this genotype develop signs and symptoms of CF88; evaluation of prospective data will help clarify the role of this mutation in NBS.93 It may be prudent to defer diagnosis of CF in these individuals but continue follow-up at a CF care center so that the diagnosis can be made if symptoms appear. Newborns with borderline sweat-test results who have only 1 or no identified CFTR mutation and newborns who have 2 CFTR mutations with sweat Cl– levels <30 mEq/L67 should be followed up similarly. This situation may be complicated by the lack of commonly accepted protocols for follow-up of infants in these groups. (Normal, borderline, and abnormal sweat-test results with suggested follow-up are discussed in more detail by Parad and Comeau.97)
In the absence of CF NBS, some infants with borderline diagnostic-test results may present later with an atypical CF diagnosis. Individuals with atypical CF tend to present with milder disease at an older age, with lower sweat Cl– levels, pancreatic sufficiency, and mild class IV or V mutations. These individuals also probably survive longer. However, the natural history of atypical CF is not well defined, and the early identification of such individuals by NBS may provide much information about the condition over time. Clinical follow-up protocols are not well established for these individuals, and the potential positive impact of CF NBS on atypical CF has not been established. Nevertheless, these infants, once brought to the attention of the CF care community, should be monitored. The follow-up proposed for such infants includes (1) a thorough evaluation by a CF physician, (2) repeat sweat testing, (3) expanded CFTR mutation analysis for all disease-producing mutations (including classes IV and V) if the sweat Cl– level remains elevated, and (4) continued follow-up at a minimum of 1 to 2 visits per year to monitor for any disease development.67
Negative Sweat-Test Results
A sweat-test result that is within the reference range (<30 mEq/L) may sometimes occur in infants with 2 CFTR mutations that were detected by CF NBS. Because the combined screening and diagnostic-test results require sophisticated analysis to interpret, and because the infant continues to have a high risk of CF, a CF specialist should meet with the family to develop a plan for evaluation and possible treatment, and genetic counseling should be offered. The NBS program must be notified immediately of the discordant result to allow an early opportunity for quality control to ensure the validity of the screening result. Genetic counseling and testing of the parents and extended family may be suggested after acute care issues have been resolved.
Some positive-screened infants with negative sweat-test results may be identified to have CF only by later clinical presentations. Clinical follow-up in parallel with repeated sweat testing and extended mutation analysis is the appropriate strategy for resolving the diagnosis in such cases. It may be more cost efficient to perform the full gene-mutation analysis immediately to establish a diagnosis for those in this group, because negative results from a limited analysis would simply prompt a more extensive screen.
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ACKNOWLEDGMENTS |
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Participants in the 2004 Workshop on Implementation of Newborn Screening in Cystic Fibrosis were Frank J. Accurso, MD (University of Colorado, Denver, CO), Mary Ann Baily, PhD (Hastings Center, Garrison, NY), Robert J. Beall, PhD (Cystic Fibrosis Foundation, Bethesda, MD), Drucy Borowitz, MD (State University of New York, Buffalo, NY), C. Michael Bowman, PhD, MD (Medical University of South Carolina, Charleston, SC), Preston W. Campbell, III, MD (Cystic Fibrosis Foundation, Bethesda, MD), Barbara Chatfield, MD (University of Utah, Salt Lake City, UT), Anne Marie Comeau, PhD (University of Massachusetts Medical School, Jamaica Plain, MA), George Cunningham, MD, MPH (California Department of Health Services, Richmond, CA [retired]), Siobhan Dolan, MD, MPH (March of Dimes, White Plains, NY), Philip M. Farrell, MD, PhD (University of Wisconsin, Madison, WI), Sumedha Ghate, MS (St Vincent Hospital, Green Bay, WI), Michael Glass, MS (Washington State Department of Health, Shoreline, WA), Scott Grosse, PhD (Centers for Disease Control and Prevention, Atlanta, GA), Ada Hamosh, MD (Johns Hopkins Hospital, Baltimore, MD), Pamela P. Hawley, MS (Children's Hospital, Boston, MA), Leslie A. Hazle, MS, RN, CPN (Cystic Fibrosis Foundation, Bethesda, MD), Gary Hoffman, BS (Wisconsin State Laboratory of Hygiene, Madison, WI), Martin Kharrazi, PhD, MPH (California Department of Health Services, Richmond, CA), Elinor Langfelder-Schwind, MS (St Vincent's Manhattan, New York, NY), Vicky LeGrys, PhD (University of North Carolina, Chapel Hill, NC), John Massie, MBBS, FRACP, PhD (Royal Children's Hospital, Parkville, Australia), Susanna A. McColley, MD (Children's Memorial Hospital, Chicago, IL), Brian P. O'Sullivan, MD (University of Massachusetts Medical Center, Worcester, MA), Richard B. Parad, MD, MPH, University of Massachusetts Medical School, Jamaica Plain, MA), Kenneth A. Pass, PhD, New York State Department of Health, Albany, NY), Suzanne R. Pattee, JD (Cystic Fibrosis Foundation, Bethesda, MD), Darci Pfiel, RN, MS, CPNP (University of Wisconsin Children's Hospital, Madison, WI), Michele A. Puryear, MD, PhD (Health Resources and Services Administration, Rockville, MD), Lynne M. Quittell, MD (Columbia University, New York, NY), Michael J. Rock, MD (University of Wisconsin, Madison, WI), Margaret Rosenfeld, MD, MPH (Children's Hospital and Regional Medical Center, Seattle, WA), Beryl J. Rosenstein, MD (Johns Hopkins Hospital, Baltimore, MD), Lainie F. Ross, MD, PhD (University of Chicago, Chicago, IL), Scott D. Sagel, MD (Children's Hospital, Denver, CO), Lisa Saiman, MD, MPH (Columbia University, New York, NY), Marci Sontag, PhD (Children's Hospital, Denver, CO), Brad Therrell, PhD (National Newborn Screening and Genetics Resource Center, Austin, TX), Monica M. Ulles, RN, PNP, CNS (Massachusetts General Hospital, Boston, MA), Terry White, PhD (Cystic Fibrosis Foundation, Bethesda, MD), and Benjamin Wilfond, MD (National Institutes of Health, Bethesda, MD).
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FOOTNOTES |
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Address correspondence to Terry B. White, PhD, Cystic Fibrosis Foundation, 6931 Arlington Rd, Bethesda, MD 20814. E-mail: tlbjww{at}att.net
The authors have indicated they have no financial relationships relevant to this article to disclose.
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