Complete Blood Count

The complete blood count (CBC) is one of the most common blood tests requested by clinicians and evaluates the total numbers and characteristics of the cell components of blood. ^[1] The test includes hemoglobin, white blood cell count, platelet count and detailed red blood cell indices, and automated analyzers also report a differential giving the percentages and absolute numbers of white blood cell subgroups. ^[2] Red cell distribution width (RDW) is a quantitative measure of the variability in size of circulating erythrocytes, with higher values reflecting greater heterogeneity in cell sizes. ^[3] The CBC is used to diagnose anemia, hematological cancers, infections, acute hemorrhagic states, allergies and immunodeficiencies, and to monitor side effects of certain drugs. ^[2] Together with review of the peripheral smear, the CBC is the foundation of laboratory hematologic diagnosis. ^[4] Primary care guidance lists the CBC among first-line or initial laboratory tests in the workup of common presentations such as chronic dyspnea and psychosis. ^{[5] [6]}

Increased systemic and local inflammation plays a key role in acute coronary syndrome, and hematological indices such as white blood cell count, neutrophil-to-lymphocyte ratio (NLR), RDW and platelet indices may provide independent information on its pathophysiology and risk stratification. ^[7] The NLR is a commonly used biomarker of acute inflammation that often rises during sepsis. ^[8] Because inflammation may play an important role in cancer progression, a high NLR has been studied, and reported, as a poor prognostic indicator in several malignancies. ^[9] RDW has been described as a routinely available biomarker of likely erythropoietic dysfunction. ^[10] The pathobiological processes that explain the predictive value of RDW remain uncertain, and a role for inflammation has been hypothesized but not established. ^[11] Increased platelet activation and a decreased platelet count are associated with many liver diseases, and in non-alcoholic

The CBC is produced by automated hematology analyzers, which must be verified for precision, accuracy, comparability, carryover, background and linearity before they are used in routine clinical care. ^[13] Expert guidance on analyzer verification also covers how laboratories establish reference intervals and run quality control, while the exact performance standard to meet is left to the laboratory specialist. ^[13] A blood smear scan serves to verify flagged automated results and to decide whether a manual differential leukocyte count is needed. ^[14] In patients with anemia, the peripheral smear allows assessment of red cell shape, size, color, inclusions and arrangement, which helps narrow the differential diagnosis across microcytic, normocytic and macrocytic anemias. ^[4] Adding a differential count and a reticulocyte count to the CBC allows the clinician to narrow the differential diagnosis and tailor further evaluation. ^[15] The platelet count reported with the CBC is a quantitative measure, so the functional status of platelets must also be considered when interpreting its clinical significance. ^[16]