Pediatrics
Utility of the peripheral blood white blood cell count for identifying sick young infants who need lumbar puncture*

Presented in part at the Pediatric Academic Society national meeting, Baltimore, MD, May 2001.
https://doi.org/10.1067/mem.2003.9Get rights and content

Abstract

Study objective: We assess the utility of the peripheral blood WBC count as a screen for lumbar puncture among young infants evaluated for serious bacterial infections. Methods: We performed logistic regression modeling and receiver operating characteristic curve analysis of peripheral blood WBC count and cerebrospinal fluid WBC count for results obtained from 3- to 89-day-old infants undergoing a full sepsis evaluation. Results: Twenty-two of 5,353 (4.1 per 1,000) infants had acute bacterial meningitis. For diagnosing acute bacterial meningitis, the peripheral blood WBC count was poorly discriminating and significantly inferior to the cerebrospinal fluid WBC count. This was true both when the odds of meningitis were modeled to vary linearly and as a U-shaped function of the peripheral blood WBC count. When relying on single and interval-based high-risk thresholds of peripheral blood WBC counts alone, the majority of infants with acute bacterial meningitis would have been missed. Conclusion: Decisions to perform or withhold lumbar puncture should not be based on prevailing interpretations of the total peripheral blood WBC counts to maximize detection of bacterial meningitis in young infants. [Ann Emerg Med. 2003;41:206-214.]

Introduction

Although rare, acute bacterial meningitis is a serious infection that continues to be a public health problem among children.1, 2 Clinical diagnosis is particularly difficult in young infants, so that preliminary analysis and routine culture of cerebrospinal fluid are recommended if such children present with a fever, hypothermia, or worrisome history or are ill appearing.3

Because parents often perceive the lumbar puncture to be more invasive than other routinely performed procedures, such as venipuncture and bladder catheterization, they might be reluctant to give consent for the test. Also, clinicians might not always be able to perform this procedure in their offices. As a result, parents often inquire about and clinicians might be inclined to use simple screening tests to determine the need to perform a lumbar puncture. It has been our impression that the peripheral blood WBC count, because of its role in detecting other serious bacterial infections and its widespread availability, is sometimes used in this manner. In this respect, clinicians might interpret the risk of meningitis to be a linear or U-shaped function of the peripheral blood WBC count.

Unfortunately, no analysis directed specifically at the overall utility of the peripheral blood WBC count for such purposes has been performed, and the likelihood of diagnosing bacterial meningitis after obtaining results within particular peripheral blood WBC count intervals has not been fully specified. In this study, we formally evaluate the validity of decisionmaking that relies on the peripheral blood WBC count alone to perform lumbar puncture and compare the discriminatory capability of this test with that of the cerebrospinal fluid WBC count among young infants evaluated for infection.

Section snippets

Methods

We analyzed the results of a computerized database in which were entered the laboratory results of consecutive infants 3 to 89 days of age evaluated for serious bacterial infection in the emergency department at Children's Hospital Boston between January 1992 and July 1999. Data were entered prospectively into a computerized database at the time of evaluation in the ED. At our institution, all infants presenting with a temperature of 38°C (100.4°F) or greater (physician referred or

Results

For the period of study, our laboratory received 5,353 consecutive cerebrospinal fluid samples for bacterial culture from children aged 3 to 89 days. Twenty-two infants met the criteria for bacterial meningitis, giving an overall prevalence of 4.1 cases per 1,000 (95% confidence interval [CI] 2.6 to 6.2). Organisms isolated included E coli (n=11), group B streptococci (n=9), S pneumoniae (n=1), and Citrobacter koseri (n=1). Only one child with meningitis, caused by E coli , was discharged after

Discussion

Our results indicate that the peripheral blood WBC count, as it is commonly interpreted, is not an accurate test for predicting bacterial meningitis in infants and performs significantly worse than the cerebrospinal fluid WBC count. Specifically, diagnosis is inaccurate both when the risk of meningitis is interpreted to vary linearly with or to have a U-shaped relationship with the peripheral blood WBC count. In addition, a strategy that combines the peripheral blood WBC count with the

References (19)

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*

Address for reprints: Bema K. Bonsu, MBChB, Division of Emergency Medicine, Children's Hospital, 700 Children's Drive, Columbus OH 43213; 614-722-4385; E-mail [email protected].

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