Pearl of the Month

What is causing my patients’ macrocytosis?


A 56-year-old man presents for his annual physical. He brings in blood work done for all employees in his workplace (he is an aerospace engineer), and wants to talk about the lab that has an asterisk by it. All his labs are normal, except that his mean corpuscular volume (MCV) is 101. His hematocrit (HCT) is 42. He has no symptoms and a normal physical exam.

What test or tests would most likely be abnormal?

A. Thyroid-stimulating hormone.

B. Vitamin B12/folate.

C. Testosterone.

D. Gamma-glutamyl-transferase (GGT).

The finding of macrocytosis is fairly common in primary care, estimated to be found in 3% of complete blood count results.1 Most students in medical school quickly learn that vitamin B12 and folate deficiency can cause macrocytic anemias. The standard workups for patients with macrocytosis began and ended with checking vitamin B12 and folate levels, which are usually normal in the vast majority of patients with macrocytosis.


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