Paper
The Complete Blood Count: Increasing Its Precision and Impact
Published Aug 1, 2023 · M. Lucijanić, I. Krečak
Annals of Internal Medicine
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Abstract
TO THE EDITOR: We enjoyed reading Burack and Lichtman's commentary (1). The complete blood count (CBC) is the main and most important tool in the hematologist's workshop and is often the sole laboratory report available when examining the patient. It is often needed to compare current CBC findings with older ones, which could be substantially complicated by the deficient CBC output proposed by the authors. Red blood cell (RBC) indices are not actually redundant. Despite having a strong positive correlation, the erythrocyte count and hematocrit and hemoglobin levels do not change equally during pathophysiologic processes that result in an elevated or reduced RBC mass. Most of the circulating blood volume is blood plasma, which represents a reservoir of inflammatory cytokines and mediators of various metabolic processes. The hematocrit– hemoglobin ratio can be used to measure hemoconcentration and dehydration (2), and a similar formula ([100 – hematocrit]– hemoglobin ratio) can be used to estimate plasma volume status (3). These have important prognostic associations, and their change over time can be used to guide diuretic therapy in patients with heart failure (3). Effects of sodium–glucose cotransporter-2 inhibitors in this context might be mediated through changes in the blood plasma volume. Mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration (MCHC), and RBC distribution width reflect the quality of erythropoiesis that is profoundly affected by both nutrient deficiencies and inflammatory conditions. They were shown to be prognostic in various inflammatory contexts, and we propose that reduced MCHC might be the “new RBC distribution width” considering its independent prognostic potential for predicting thrombotic events (4). Particular CBC indices have an established and validated role in the diagnosis and evaluation of patients with specific diseases—for example, hematocrit in polycythemia vera, the total leukocyte count in sepsis and the prognosis of myelofibrosis, and the absolute and relative monocyte count in chronic myelomonocytic leukemia. We have encountered several patients who were referred to a hematologist because of an elevated relative lymphocyte count who instead actually had neutropenia and normal lymphocytes in absolute terms, which led to further work-up and recognition of underlying diseases. Finally, with the advent of such novel technologies asmachinelearning, previously neglected values are emerging as important predictors of particular diseases or unwanted outcomes. For example, a recent analysis of patients with polycythemia vera from the U.S. Optum database (5) led to RBC distribution width and neutrophil and lymphocyte percentages being recognized as important predictors of thromboembolic events in patients treated with hydroxyurea. The CBC thus represents a simple, widely available, and powerful tool that provides insight into the biology of the human organism. Its role transcends the evaluation of anemia, provided that we have access to all of its values.
The complete blood count (CBC) is a valuable tool for hematologists, with various indices playing crucial roles in diagnosis and evaluation of patients with specific diseases.
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