Laboratory Data

1. CBC with differential. Often overutilized in well-appearing febrile children. Total WBC is a risk factor for bacteremia in highly febrile child. Low total WBC is not a reliable predictor of meningitis because low WBC counts are seen in viral infection, overwhelming infection (including meningitis), and immune deficiency states.

2. Lumbar puncture. Remains the gold standard for diagnosis of meningitis and must be performed, if not contraindicated, when history and physical exam cannot convincingly rule out bacterial meningitis.

3. Blood culture. Has little practical value to assess for occult bacteremia (bacteremia unexpected on clinical grounds). Most of these episodes are benign and resolve without treatment. Children who develop serious deep infections often present for medical care before positive testing of the blood culture. Multiple (three or four) blood cultures are warranted when certain diseases (eg, osteomyelitis, endocarditis) are suspected to increase their yield. Blood cultures should be obtained through central lines if present.

4. Urinalysis. A useful test in female children without other evidence of infectious foci; it has a significantly lesser yield in male children but should be considered in uncircumcised boys during infancy if fever is not self-limited. Urine nitrites, leukocyte esterase, Gram stains, and direct cell visualization add to the immediate diagnostic value of urinalysis.

5. Urine culture. The gold standard for diagnosing UTI.

6. Other cultures. Throat culture and rapid antigen tests can be useful in diagnosing streptococcal pharyngitis; occasional culture from the maximum area of induration of a cellulitis yields an infecting organism. Stool culture in selected patients may lead to a diagnosis of enteric infection (bloody diarrhea, elevated fecal leukocytes, or protracted diarrhea).

7. Miscellaneous tests. Consider cultures of central lines, if present. Hepatic transaminases may suggest viral disease and lead to more specific hepatitis studies. C-reactive protein and ESR, although nonspecific, can occasionally help direct diagnoses or assess progress of treatment in some infectious diseases.

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