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* Harvard Pediatric Health Services Research Fellowship
Department of Surgery
¶ Division of General Pediatrics, Childrens Hospital Boston, Boston, Massachusetts
Department of Surgery, Brigham and Womens Hospital, Boston, Massachusetts
|| Department of Ambulatory Care and Prevention, Harvard Pilgrim Health Care and Harvard Medical School, Boston, Massachusetts
| ABSTRACT |
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Methods. The Kids Inpatient Database is a national sample of pediatric discharges from 2521 hospitals in 22 states in 1997. In this study, misdiagnosis was defined as a patient with a principal International Classification of Diseases, Ninth Revision procedure code for nonincidental appendectomy without a corresponding diagnosis code for appendicitis. Hospitals were stratified into 5 groups based on the number of nonincidental appendectomies performed on children in 1997: lowest (<1 per month), low (
1 per month but <1 per week), medium (12 per week), high (23 per week), and highest (
3 per week). Using generalized estimating equations to control for clustering within hospitals, we developed a logistic regression model of the effect of hospital volume on misdiagnosis while adjusting for patient age, gender, race, and insurance status.
Results. In the database, 37 109 nonincidental appendectomies were performed on children 1 to 18 years old in 1997. Of those, 3103 (8.4%) were misdiagnosed. Of all appendectomies, 24 655 (66.4%) were performed at lowest- or low-volume hospitals. After adjusting for patient characteristics, lowest- (odds ratio [OR]: 1.5; 95% confidence interval [CI]: 1.02.2) and low- (OR: 1.6; 95% CI: 1.12.3) volume hospitals had a significantly increased likelihood of misdiagnosis compared with highest-volume hospitals. Misdiagnosis at medium- (OR: 1.5; 95% CI: 1.02.2) and high- (OR: 1.4; 95% CI: 0.92.2) volume hospitals was similar to misdiagnosis at lower-volume hospitals, although not statistically different from highest-volume hospitals.
Conclusions. Almost two thirds of pediatric appendectomies are performed at hospitals performing <1 pediatric appendectomy per week. Lower hospital volume of pediatric appendectomies is associated with a significantly increased likelihood of misdiagnosis of appendicitis in children.
Key Words: appendicitis misdiagnosis volume outcome
Abbreviations: KID, Kids Inpatient Database ICD-9, International Classification of Diseases, Ninth Revision OR, odds ratio CI, confidence interval
Appendicitis is common in children, but it is often misdiagnosed. Of the >70 000 pediatric appendectomies performed annually in the United States,1 as many as 24% are negative appendectomies, revealing a normal appendix.25 Such rates of misdiagnosis are accepted because of the common belief that a reduction in the incidence of misdiagnosis results in an increase in appendiceal perforation and its complications.6 Furthermore, misdiagnosis is accepted because many clinicians consider a negative appendectomy to have few harmful effects. Some studies now question the inverse relationship between these 2 outcomes, suggesting that misdiagnosis can be improved without affecting the risk of perforation.79 In addition, recent research shows that the misdiagnosis of appendicitis has considerable clinical and economic costs.10
Studies have demonstrated an association between higher hospital volume and improved patient outcome for certain surgical procedures.1113 Based on this research, the Leapfrog Group, a consortium of public and private purchasers of health insurance, encourages patients to be treated at high-volume centers for certain procedures.14 Although most volume-outcome research has focused on adult procedures, recent investigations have suggested a similar relationship between volume and outcome in pediatric conditions.1518 Nonetheless, the effect of hospital volume on outcome is not known for the majority of pediatric surgical procedures. In this study we test the hypothesis that higher hospital volume of pediatric appendectomies is associated with lower rates of misdiagnosis of appendicitis in children.
| METHODS |
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18 years old. From each hospital in the database, the KID contains a random sample of 80% of pediatric nonbirth discharges. For each discharge, the database includes up to 15 diagnosis and 15 International Classification of Diseases, Ninth Revision (ICD-9) procedure codes, with the first code representing the principal diagnosis or procedure.19 The study cohort consisted of children 1 to 18 years old with a principal ICD-9 procedure code for nonincidental appendectomy: 47.0 (appendectomy), 47.01 (laparoscopic appendectomy), or 47.09 (other appendectomy).20 Patients undergoing an incidental appendectomy (an appendectomy at the time of another procedure) were identified with separate ICD-9 codes and were not included in the analysis. Two patients with no gender reported were excluded from the analysis. For other variables with missing data, we included a separate category indicating missing values. Analysis of race, the most commonly unreported variable, showed that 91% of the 7882 patients with unreported race were treated at hospitals that did not report race for any of their patients. The characteristics of these hospitals were similar to the other hospitals in our sample, so patients with missing race were included. In addition, we assessed the sensitivity of our final results by repeating the analysis with patients with missing race excluded.
A case of appendicitis was defined by a diagnosis code for appendicitis: 540.0 (acute appendicitis with generalized peritonitis), 540.1 (acute appendicitis with peritoneal abscess), 540.9 (acute appendicitis without mention of peritonitis), 541 (appendicitis, unqualified), and 542 (other appendicitis).20 We assumed that a patient having one of these discharge diagnosis codes was diagnosed correctly with appendicitis at the time of surgery. The remaining appendectomy patients did not have a discharge diagnosis code for appendicitis. These patients were classified as misdiagnosed in accordance with previous studies.21,22 Misdiagnosis was the primary outcome in our analysis.
For every hospital in the database, we determined the number of nonincidental pediatric appendectomies performed in 1997. Because the KID contains a random 80% sample of all nonbirth discharges, the estimated annual volume of appendectomies was calculated for each hospital by multiplying the KID volume of appendectomies by 1.25. Hospital volume was analyzed as both a continuous and a categorical variable; because both approaches yielded similar results, only the categorical results are presented. Hospitals were categorized into 5 mutually exclusive volume groups based on the estimated annual hospital volume of pediatric appendectomies: lowest (<1 appendectomy per month), low (at least 1 appendectomy per month but <1 per week), medium (at least 1 but <2 appendectomies per week), high (at least 2 but <3 appendectomies per week), and highest (
3 appendectomies per week). We selected these categories to represent the spectrum of hospital frequency of pediatric appendectomies before analysis of hospital characteristics or misdiagnosis rates. Highest-volume hospitals were used as the reference group.
We considered patient age, gender, race, zip code median income, insurance payer, and transfer from another hospital as covariates in our analysis. We categorized these variables as shown in Table 1. The treating hospitals classification as a teaching hospital was considered in our analysis as well. We report childrens hospital status but did not include this variable in the bivariate or multivariate analyses. Patient characteristics were compared among hospital volume levels by using analysis of variance and Cochrane-Armitage tests of trend.
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The research protocol was approved as exempt from review by the institutional review boards of Childrens Hospital Boston and Harvard Pilgrim Health Care.
| RESULTS |
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Of the 37 109 patients, 3103 (8.4%) were misdiagnosed (Table 1). The most common principal discharge diagnoses for patients who were misdiagnosed include other abdominal symptoms or conditions: unexplained abdominal pain (35.1%), mesenteric adenitis (22.8%), lymphoid hyperplasia (10.6%) or other diseases of the appendix (9.9%), gastroenteritis (4.4%), and ovarian cyst (3.3%).
Patient and hospital characteristics varied among volume categories (Table 2). The 24 childrens hospitals ranged in volume from low to highest, with 8 (33%) in the highest-volume category. Teaching hospitals were represented in all hospital volume categories. The mean age of patients decreased with increasing hospital volume levels (P for trend < 0.001), whereas the percentage of Medicaid-insured patients increased (P for trend < 0.001).
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In addition to hospital volume, the final adjusted model included gender, age, gender/age interaction, race, and insurance status (Table 4). The effect of gender on misdiagnosis differed across age groups. Compared with 15- to 18-year-old males, 10- to 14- and 15- to 18-year-old females had significantly increased odds of misdiagnosis (OR: 2.3; 95% CI: 2.02.6; P < .01 and OR: 3.3; 95% CI: 2.93.8; P < .01, respectively). In the 1- to 4- and 5- to 9-year-old age groups, both males and females had an increased likelihood of misdiagnosis compared with the reference group, 15- to 18-year-old males. Race also had a significant effect, with misdiagnosis less common in Hispanics (OR: 0.57; 95% CI: 0.500.65; P < .01) and patients of other minority races (OR: 0.66; 95% CI: 0.540.81; P < .01) compared with whites. In this analysis, insurance status did not have a significant effect on misdiagnosis.
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| DISCUSSION |
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This study also provides useful insight into the distribution of pediatric appendectomies among hospitals. Of the 2521 hospitals included in the KID, 2217 performed at least 1 pediatric appendectomy in 1997. Most (91.7%) of these hospitals were lowest- or low-volume by our classification, performing <1 pediatric appendectomy per week. However, these lowest- and low-volume hospitals performed 66% of all appendectomies. Thus, the majority of pediatric appendectomies occur at hospitals that perform them infrequently. Although patient and hospital characteristics varied among hospital volume levels, our analysis was designed to adjust for these factors.
In addition to showing that higher hospital volume is associated with a lower risk of misdiagnosis, this study demonstrates the importance of patient characteristics as well. Infants and young children, who might not be able to describe their symptoms, have an increased risk of misdiagnosis, as do adolescent females, in whom the diagnosis can be complicated by gynecological and obstetric conditions. We found that Hispanics and patients of other minority races have significantly decreased odds of misdiagnosis. One possible explanation for these results is that cultural beliefs, language barriers, or limited access to medical care cause patients of minority race to seek care later in the course of their disease. At advanced stages, appendicitis is generally easier to diagnose, making misdiagnosis less common in this group. Because the KID includes only 22 states, the racial and ethnic distribution in our sample does not represent the entire US population, which may affect our ability to generalize the race and ethnicity results. Further work in other patient samples is needed to confirm and clarify these results.
Ours is the first investigation to focus primarily on the relationship between hospital volume and misdiagnosis of pediatric appendicitis. Although our conclusions contrast with a previous study, hospital volume was not a focus of that analysis.4 Here we contribute data from a large, nationally representative sample of pediatric patients and hospitals. We were able to control for many of the patient characteristics that influence misdiagnosis. Our volume categories were selected to represent a natural breakdown of hospital frequency of appendectomies and to be reproducible for use in future analyses. These categories did not result in the separation of childrens or teaching hospitals into any single volume category.
As with any study using administrative data, this analysis has limitations. We did not have final pathology reports to confirm the presence or absence of appendicitis. To be consistent with the existing literature, we used the ICD-9 code definitions of appendicitis and misdiagnosis that have been described previously.21,22 Patients with a normal appendix could have been miscoded as having appendicitis or vice versa. Moreover, we assumed that all patients with an ICD-9 code for a nonincidental appendectomy were treated for suspected appendicitis. Some appendectomies may have been performed for another purpose or as part of another procedure. In an attempt to minimize the miscoding of procedures, we modified the definition of appendectomy used by Addiss et al21 and Flum et al22 to include only patients with a principal procedure of nonincidental appendectomy excluding those for whom appendectomy was listed as a secondary procedure.
We were surprised somewhat by the low misdiagnosis rate in our sample, which may differ from studies that used sources other than claims data. Because of the potential sources of misclassification, the absolute misdiagnosis rate in our analysis may not reflect the misdiagnosis rate in the pediatric population precisely. Nonetheless, the misdiagnosis rate seen here was within the range of published series,25 and the principal diagnoses of misdiagnosed patients were consistent with clinical expectations. Our main objective was to compare relative rates of misdiagnosis across hospitals. There is no reason to expect that the miscoding of diagnoses and procedures is more common at any hospital volume level. In fact, no systematic coding errors were detected in an audit of pediatric coding in New York.16 As long as systematic coding errors do not exist, comparisons of misdiagnosis across hospitals should be valid.
Other factors such as the volume of appendectomies per surgeon, childrens hospital status, or hospital location or region could have contributed to the diagnostic accuracy seen at highest-volume hospitals. Our goal was to focus on hospital volume, the major component of recent quality initiatives,14 rather than other characteristics that could be associated with volume. Although childrens hospitals may possess specific qualities that improve diagnostic accuracy, we were unable to control for childrens hospital status in our model due to colinearity with volume. We did not control for volume of procedures per surgeon, because these data were not available in the KID. In addition, our hospital volume calculations did not include adult appendectomies. Some of our low-volume hospitals may have performed large numbers of adult appendectomies. Because of limitations of the database, hospital volume of adult appendectomies was not available. We believe, however, that because of the differences between children and adults, pediatric appendectomy volume is the most relevant volume measure to associate with the misdiagnosis of pediatric appendicitis.
We used 1997 data, the most recent data available at the time of our analysis. Increased utilization of imaging studies and clinical algorithms could have resulted in changing diagnostic strategies in recent years, suggesting the need for similar analyses as more current data become available.
A hypothetical application of the diagnostic accuracy of highest-volume hospitals to patients treated at lowest- and low-volume hospitals yields interesting insights. Of the 24 655 children treated at lowest- and low-volume hospitals, 2187 were misdiagnosed. Our data suggest that if the diagnostic accuracy seen at highest-volume hospitals were available at lowest- and low-volume institutions, only 1453 of those children would be expected to have been misdiagnosed, implying that 734 unnecessary appendectomies could have been avoided. Of note, improved diagnostic accuracy at highest-volume hospitals may be reflected in increased costs. This must be weighed against the clinical and economic costs that have been associated with misdiagnosis.10
We are not recommending that all children with appendicitis be treated at highest-volume centers. The highest-volume hospitals do not have the capacity to treat these additional patients, and many patients do not have timely access to a highest-volume hospital. We do not know whether the lower rates of misdiagnosis at highest-volume hospitals are a result of differences in clinical skills, diagnostic testing patterns, or other processes of care. A previous study showed that care in a group of hospitals can be improved by identifying the best clinical practices at member institutions.25 Performing such an analysis of highest-volume hospitals could enable dissemination of their most successful processes of care, resulting in improved diagnosis of pediatric appendicitis at all hospital-volume levels.
| CONCLUSIONS |
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| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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Reprint requests to (S.J.F.) Department of Surgery, Childrens Hospital Boston, 300 Longwood Ave, Boston, MA 02115. E-mail: steven.fishman{at}tch.harvard.edu
| REFERENCES |
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