Muhammad Numan: Normal MCV Does Not Exclude B12 Deficiency
Muhammad Numan, Junior Medical Technologist at Shaukat Khanum Memorial Cancer Hospital and Research Centre, shared a post on LinkedIn:
”Case Study: Hypersegmented Neutrophils Despite Normal MCV – The Diagnostic Value of Peripheral Blood Smear Examination
Clinical Presentation and Initial CBC Findings
A CBC sample was received in the hematology section for routine evaluation.
Automated CBC analysis revealed anemia (Hemoglobin 9.1 g/dL) with a normal MCV of 84.5 fL, reduced platelet count (52 ×10³/µL), and increased RDW (22.4 percent).
Although Vitamin B12 and folate deficiency are classically associated with macrocytosis, the patient’s MCV remained within the normal reference range.
Because hematological indices alone did not fully explain the findings, a peripheral blood smear examination was performed for morphological assessment.
Peripheral Blood Smear Examination
Microscopic examination of the peripheral blood smear demonstrated a dimorphic population of RBCs with aniso-poikilocytosis, elliptocytes, and tear drop cells.
White blood cells were adequate and showed hypersegmented neutrophils.
Platelets appeared reduced with no evidence of platelet clumping.
The differential leukocyte count was verified manually before releasing the report.
Morphological Interpretation and Clinical Correlation
Hypersegmented neutrophils are a well-recognized morphological feature of Vitamin B12 and folate deficiency and may appear 2–3 weeks before the development of macrocytosis.
This occurs because neutrophils have a much shorter lifespan (hours to days), whereas red blood cells survive for approximately 120 days.
Consequently, early megaloblastic changes may be detected on peripheral blood smear while the MCV remains within the normal reference range, as observed in this case (84.5 fL).
This highlights the importance of correlating automated CBC parameters with careful microscopic examination rather than relying solely on red cell indices.
Final Laboratory Comment
Peripheral smear shows Dimorphic population of RBCs with aniso-poikilocytosis, elliptocytes and tear drop cells.
WBCs adequate with Hyper segmented Neutrophils seen. Platelets reduced with no clumps.
MPV is a calculated parameter, value are missing due to platelet anisocytosis. Serum Vitamin B12 and Folate levels are recommended. Clinical Correlation is advised.
Learning Point
Vitamin B12 and folate deficiency are commonly expected to present with macrocytosis and an elevated MCV.
However, hypersegmented neutrophils may be the earliest hematological manifestation, appearing before changes in red cell indices become evident.
This case demonstrates that a normal MCV does not exclude early megaloblastic change and reinforces the indispensable role of peripheral blood smear examination in identifying subtle morphological abnormalities.
Careful smear review, combined with clinical correlation, allows the Medical Laboratory Scientist to detect early diagnostic clues that may not be recognized by automated CBC parameters alone.”
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