Value of the leukocyte count in predicting mortality of patients with community-acquired bacteremia

Study objectives: The overall leukocyte and immature neutrophil count is commonly measured in the emergency department and is often considered to be a predictor of severe illness. We determine the value of an elevated or decreased total leukocyte count in predicting the mortality of patients with community-acquired bacteremia. Methods: Demographic and laboratory data were gathered from 2 hospitals on 806 consecutive patients aged 1 day to 101 years with positive blood culture results. Total leukocyte and immature neutrophil count were measured within 24 hours of the index culture. Clinical outcomes, including mortality and clinical significance, were monitored throughout hospitalization and compared by χ2 analysis or Wilcoxon rank-sum tests, as appropriate. Results: In 314 of the patients, the organism recovered was eventually determined to be a contaminant. The remaining 492 (61%) patients were diagnosed with and treated for bacteremia. Overall inhospital mortality for patients with bacteremia was 13%. The all-cause mortality rate of patients with a normal leukocyte count (4,500 to 12,499/mL3) was 10.3%. There was no significant difference in the mortality rate for patients with high leukocyte counts (>12,499/mL3, 10.9%); however, the mortality rate for patients with a low WBC count (<4,500) was more than twice that of the other groups (P=.02, 23.5%). Percent immature neutrophils provided some predictive information, but not until it reached a level of greater than 20%, which occurred in only 12.2% of the patients with bacteremia (23% mortality rate). Conclusion: Elevation of the absolute leukocyte count does not predict mortality in patients with community-acquired bacteremia. Patients with suspected bacteremia and a low absolute leukocyte count or very high percentage of immature neutrophils are at increased risk of a poor outcome.