Q&A column

Editor: Frederick L. Kiechle, MD, PhD

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Q. Automated differentials are broken down into absolute counts for neutrophils, lymphocytes, monocytes, eosinophils, and basophils. The absolute neutrophil count is a useful index for physicians in clinical decision-making. When performing a manual differential that contains immature cells such as metamyelocytes and myelocytes, do you report an absolute count on all of the individual cells in the myelocytic line, or do you group them together and calculate one ANC? What about lymphocytes and reactive lymphocytes?

A. White blood cell differential counts, traditionally performed manually, were reported as percentages of total WBCs. Given the potential issues in interpreting percentages, including errors in manual calculations of absolute counts, together with readily available absolute counts on automated CBC analyzers, reporting absolute differential counts is recommended.¹ Automated CBC analyzers typically provide a five-part or six-part differential count including absolute neutrophil count, absolute monocyte count, absolute lymphocyte count, absolute eosinophil count, absolute basophil count, and, in some platforms, absolute immature granulocyte count.

An absolute neutrophil count, or ANC, historically calculated from manual differentials, is: total WBC count × (% segmented neutrophils + % bands)/100. This is the calculation used to define thresholds for neutropenia and its significance in early clinical studies.^2,3 When providing manual ANCs, the calculations should therefore include neutrophils and bands but not other immature granulocytes (i.e. metamyelocytes, myelocytes, promyelocytes). Immature granulocytes, when present, may be reported as their individual absolute counts (i.e. absolute metamyelocyte count, absolute myelocyte count, absolute promyelocyte count), or combined into one absolute immature granulocyte count. On the other hand, total granulocyte count includes immature granulocytes and is calculated as: total WBC count × (% segmented neutrophils + % bands + % myelocytes + % metamyelocytes + % promyelocytes)/100.