Clinical meaning
The complete blood count (CBC) evaluates three cell lines produced by bone marrow hematopoiesis from pluripotent stem cells. The RBC lineage is assessed by hemoglobin (Hgb), hematocrit (Hct), MCV (mean corpuscular volume classifying anemias as microcytic <80 fL, normocytic 80-100 fL, or macrocytic >100 fL), MCH, MCHC, RDW (red cell distribution width indicating anisocytosis), and reticulocyte count (reflecting marrow response). The WBC lineage includes neutrophils (bacterial infection, first responders), lymphocytes (viral infection, adaptive immunity), monocytes (chronic inflammation, phagocytosis), eosinophils (parasites and allergies), and basophils (hypersensitivity). Platelets (thrombocytes) are megakaryocyte fragments essential for primary hemostasis; the MPV (mean platelet volume) helps differentiate causes of thrombocytopenia (large platelets suggest peripheral destruction; small platelets suggest underproduction).
Diagnosis & workup
Diagnostics & workup: - CBC with differential: automated WBC count, Hgb, Hct, MCV, MCH, MCHC, RDW, platelet count - Peripheral blood smear: morphology assessment (schistocytes in TTP/HUS/DIC, target cells in thalassemia/liver disease, spherocytes in hereditary spherocytosis/AIHA, hypersegmented neutrophils in B12/folate deficiency) - Reticulocyte count: elevated (>2% or reticulocyte production index >2) indicates appropriate marrow response to anemia (hemolysis, blood loss); low indicates underproduction - Iron studies: serum iron, ferritin, TIBC, transferrin saturation (iron deficiency: low ferritin, high TIBC, low saturation; anemia of chronic disease: normal/high ferritin, low TIBC) - B12 and folate levels for macrocytic anemia; methylmalonic acid and homocysteine to differentiate (MMA elevated only in B12 deficiency) - Haptoglobin (decreased in hemolysis), LDH (elevated in hemolysis), indirect bilirubin, direct Coombs test (positive in autoimmune hemolytic anemia) - Bone marrow biopsy for unexplained cytopenias, suspected malignancy, or pancytopenia