CBC Interpretation

A CBC is a snapshot of the concentration of circulating blood cells. It does not directly reveal how quickly the marrow is producing cells, whether cells are being destroyed, whether blood has been lost, or whether plasma volume has changed. Interpretation therefore starts with the patient and the trend, not with an isolated flagged value. Compare the result with the patient’s previous CBC, current symptoms, medication exposure, hydration, bleeding history, and the reason the test was ordered. A haemoglobin of 95 g/L may be a stable baseline for one patient and evidence of active haemorrhage in another. A platelet count that falls from 300 to 150 × 10⁹/L remains within many laboratory reference intervals but represents a 50% decline and may signal heparin-induced thrombocytopenia. The three cell lines are: - Red cells: haemoglobin, haematocrit, red-cell indices, and reticulocytes. - White cells: total leukocyte count and differential, with particular attention to the absolute neutrophil count (ANC). - Platelets: platelet count and, when helpful, mean platelet volume (MPV). Haemoglobin is the most clinically useful measure of oxygen-carrying capacity. Haematocrit generally changes in...