Hypersegmented Neutrophils and Vitamin B ₁₂ Deficiency

The sensitivities and specificities of the mean cell volume (MCV), the red cell distribution width (RDW), and blood smear hypersegmentation for B₁₂ deficiency were reviewed in 515 patients whose B₁₂ levels were determined. 61 patients had B₁₂ levels less than 200 pg/ml. 43 patients were defined as B₁₂ deficient (n = 13) or non- B₁₂ deficient (n = 30). Hypersegmentation was more sensitive (91 %) than MCV > 95 fl (62%) or RDW > 15% (54%) in detecting B₁₂ deficiency. The MCV and the RDW should not be relied on when screening for B₁₂ deficiency; examination of the blood smear for hypersegmentation is essential.