A CBC shows Hgb 140 g/L, Hct 0.340 L/L (↓), MCV 72 fL (↓), MCHC 411 (↑). With no history of abnormalities, what is the most likely cause?

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Multiple Choice

A CBC shows Hgb 140 g/L, Hct 0.340 L/L (↓), MCV 72 fL (↓), MCHC 411 (↑). With no history of abnormalities, what is the most likely cause?

A preanalytical artifact is the most likely explanation when the CBC shows microcytosis (low MCV) with an abnormally high MCHC. An excess of EDTA in the collection tube can cause red blood cells to lose water and shrink. This dehydration lowers the cell volume (lower MCV) and the overall packed cell volume (lower Hct), while concentrating hemoglobin inside the smaller cells, which artificially raises the MCHC. In true iron deficiency, you’d expect low MCV and typically low or normal MCHC, not a markedly elevated MCHC. Since there’s no abnormal history and the indices pattern fits an in vitro artifact, excess EDTA is the best explanation.

A preanalytical artifact is the most likely explanation when the CBC shows microcytosis (low MCV) with an abnormally high MCHC. An excess of EDTA in the collection tube can cause red blood cells to lose water and shrink. This dehydration lowers the cell volume (lower MCV) and the overall packed cell volume (lower Hct), while concentrating hemoglobin inside the smaller cells, which artificially raises the MCHC. In true iron deficiency, you’d expect low MCV and typically low or normal MCHC, not a markedly elevated MCHC. Since there’s no abnormal history and the indices pattern fits an in vitro artifact, excess EDTA is the best explanation.

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