Neutropenia: The accuracy and precision of the neutrophil count in leukopenic patients

Neutropenia (absolute neutrophil count < 500/μl) is a life threatening clinical state commonly seen in cancer and leukemia patients on intensive chemotherapy. The purpose of this investigation is to determine the accuracy and precision of the absolute neutrophil count in these patients using two methods: (1) the percentage of neutrophils as determined by a 100 cell manual differential multiplied by the white blood cell count (NEUT‐M), and (2) the absolute neutrophil count determined directly by automated flow cytometry using the Hemalog‐D automated white cell differential counter (NEUT‐D) Technicon Instruments Corp., Tarrytown, NY. The coefficient of variation (cv) for repeated measurements was dependent on absolute neutrophil count. For manual determinations, the cv was 5% at 5000/μl, 18% at 500/μl, and 42% at 50/μl. For the cytometry method the cv was 2.5% at 5000/μl, 8% at 500/μl, and 17% at 50/μl. The accuracy of flow cytometric differential neutrophil counts using the Hemalog‐D system was found to be equivalent to the manual differential count. The precision, however, was more than twice that of the manual white cell differential count. In the neutropenic patient this analytical improvement was clinically useful as demonstrated by sequential observation of daily neutrophil counts.