When the Numbers Lie: Spurious CBC Results | AI Learning Guide

Not every abnormal CBC reflects the patient's biology. Cold agglutinins are antibodies that clump red cells at room temperature. The analyzer counts these clumps as single large cells, which falsely raises the MCV and falsely lowers the red cell count, while the hemoglobin stays accurate. The clue is a high MCV that does not fit the clinical picture, often with a high MCHC. Warming the sample to thirty-seven degrees and rerunning corrects it. Lipemia or a very high white cell count can scatter light and falsely elevate the hemoglobin, which can mask a true anemia. A clotted sample, from poor mixing or an underfilled tube, produces small clots counted as cells and gives falsely low counts. The practical rule: when the CBC does not fit the clinical picture, repeat it and inspect the sample before accepting the numbers.

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Three common causes of spurious CBC results

Cold agglutinins: red cell clumping falsely raises MCV and MCHC and lowers the red cell count; warm the sample to 37 degrees Celsius and rerun.
Lipemia or marked leukocytosis: turbidity or light scattering falsely elevates hemoglobin, potentially masking anemia; the indices are usually unaffected.
Clotted sample: inadequate mixing or an underfilled tube produces small clots counted as cells, giving falsely low counts and unreliable indices; inspect the tube and recollect.

When the CBC does not fit the clinical picture, repeat it and inspect the sample before accepting the numbers. A result that contradicts the history is more often a technical problem than a new disease.