Published online October 2, 2006
PEDIATRICS Vol. 118 No. 4 October 2006, pp. 1798a-1799 (doi:10.1542/peds.2006-2101)

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LETTER TO THE EDITOR

Predictors of Fatality in Hemolytic Uremic Syndrome Lack Numbers: In Reply

Robert S. Oakes, BS
Division of Nephrology

Andrew T. Pavia, MD
Division of Infectious Disease
Department of Pediatrics
University of Utah
Salt Lake City, UT 84132

We appreciate the thoughtful comments of Drs Harrington, Hawkes, and Al-Odayani regarding our study of risk factors for death among children with hemolytic uremic syndrome.¹ Harrington correctly highlights the limitations of a study that included patients over a 33-year period and included small numbers of deaths, variations in data collection, and changes in medical practice. We agree that great care should be used before generalizing from a retrospective study in one region to current practice. Nonetheless, the factors we identified may generate hypotheses for future studies and may help identify patients whose conditions warrant early transfer to a tertiary care center.

Harrington's careful review of Table 3 identified several embarrassing inconsistencies between the text and the table that resulted from not excluding missing values from some calculations in the table. These inconsistencies were also noted by Hawkes and Al-Odayani. We reviewed the tables and text as well as the raw data, tabulations, and statistical calculations. A corrected version of Table 3 from the manuscript is included below.

View this table: [in this window] [in a new window]   TABLE 3 Clinical Characteristics on Admission to Hospital: Acute-Phase Fatalities Compared With Survivors

 
Hawkes and Al-Odayani raise the important issue of the distinction between relative risk (RR) and odds ratio (OR). Our study can be viewed as a retrospective cohort study in which all children with hemolytic uremic syndrome in the region during the study period form the cohort, and some develop the outcome of interest (death).² As such, it is legitimate to directly calculate the RR (or rate ratio) of death among subjects with an exposure compared with those without that exposure. The OR, as Hawkes and Al-Odayani note, indicates the odds of exposure in a person with disease relative to the odds of exposure in a person without the disease. ORs approximate the RR when the disease is rare and can be used in both case-control and cohort studies. Another reason for the popularity of the OR in cohort studies is that it can be estimated from logistic-regression analysis. Thus, although we believe this was an important discussion for the journal club, both measures of association are valid in this study. ORs for the categorical predictors are included in the revised table. Although the point estimates differ, the conclusions are similar and the confidence intervals for the point estimate of both parameters overlap.

As Hawkes and Al-Odayani point out, oligoanuria and dehydration were not independent predictors in logistic-regression models that included hematocrit >23% and white blood count >23 x 10⁹/L. However, what we briefly mention in our discussion is exploration of a combination of variables that provided the greatest sensitivity and specificity for death. The presence of dehydration and oliguria with elevated hematocrit and white blood count most accurately identified the children who died. The presence and duration of oligoanuria and the need for dialysis have been associated with chronic sequelae and death in other studies.^3–5

REFERENCES

1. Oakes RS, Siegler RL, McReynolds MA, Pysher T, Pavia AT. Predictors of fatality in postdiarrheal hemolytic uremic syndrome. Pediatrics. 2006;117 :1656 –1662[Abstract/Free Full Text]

2. Rothman KJ. Modern Epidemiology. Boston, MA: Little Brown; 1986

3. Robson WL, Leung AK, Brant R. Relationship of the recovery in the glomerular filtration rate to the duration of anuria in diarrhea-associated hemolytic uremic syndrome. Am J Nephrol. 1993;13 :194 –197[Web of Science][Medline]

4. Siegler RL, Pavia AT, Hansen FL, Christofferson RD, Cook JB. Atypical hemolytic-uremic syndrome: a comparison with postdiarrheal disease. J Pediatr. 1996;128 :505 –511[CrossRef][Web of Science][Medline]

5. Garg AX, Suri RS, Barrowman N, et al. Long-term renal prognosis of diarrhea-associated hemolytic uremic syndrome: a systematic review, meta-analysis, and meta-regression. JAMA. 2003;290 :1360 –1370[Abstract/Free Full Text]

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PEDIATRICS (ISSN 1098-4275). ©2006 by the American Academy of Pediatrics

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This Article Extract Full Text (PDF) Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services E-mail this article to a friend Similar articles in this journal Alert me to new issues of the journal Add to My File Cabinet Download to citation manager Request Permissions Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Oakes, R. S. Articles by Pavia, A. T. Search for Related Content PubMed Articles by Oakes, R. S. Articles by Pavia, A. T. Related Collections Infectious Disease & Immunity Related AAP Red Book topics: Escherichia coli Diarrhea... Social Bookmarking                         What's this?