Background: Hospital clinical laboratories increasingly use automated hematology analyzers to perform complete blood cell counts. However, automated analyzers cannot directly measure immature forms of neutrophils. A manual white blood cell count (WBC) differential is performed only when a specimen is flagged by the instrument as a result of high or low cell counts. This study was designed to determine how often significant elevations in the number of band form neutrophils were missed by current laboratory procedures.
Methods: This study compared the number of immature neutrophils found by processing the WBC as dictated by the automated analyzer versus manual WBC differentials by study technologists on the same specimens. The patient population was 101 consecutive patients with positive blood cultures.
Results: In 46 of 101 patients, the automated analyzer dictated a manual WBC differential. In the other 55 patients, the manual differential demonstrated 14% to 44% band forms in 24 patients. In a subset of 11 patients with a normal WBC, the manual differential showed band counts between 18% and 45% in 7 patients.
Conclusions: White blood cell counts performed by a modern hematology analyzer failed to lead to the detection of a significant increase in band counts in 24% of 101 bacteremic patients. In suspected bacteremic patients, it seems reasonable for physicians to mandate performance of a manual WBC differential.