Evaluation of macrocytosis

Am Fam Physician. 2009 Feb 1;79(3):203-8.


Macrocytosis, generally defined as a mean corpuscular volume greater than 100 fL, is frequently encountered when a complete blood count is performed. The most common etiologies are alcoholism, vitamin B12 and folate deficiencies, and medications. History and physical examination, vitamin B12 level, reticulocyte count, and a peripheral smear are helpful in delineating the underlying cause of macrocytosis. When the peripheral smear indicates megaloblastic anemia (demonstrated by macro-ovalocytes and hyper-segmented neutrophils), vitamin B12 or folate deficiency is the most likely cause. When the peripheral smear is non-megaloblastic, the reticulocyte count helps differentiate between drug or alcohol toxicity and hemolysis or hemorrhage. Of other possible etiologies, hypothyroidism, liver disease, and primary bone marrow dysplasias (including myelodysplasia and myeloproliferative disorders) are some of the more common causes.

Publication types

  • Review

MeSH terms

  • Alcohol Drinking / adverse effects
  • Algorithms
  • Anemia, Macrocytic / blood
  • Anemia, Macrocytic / diagnosis*
  • Anemia, Macrocytic / etiology*
  • Anemia, Megaloblastic / diagnosis
  • Anemia, Megaloblastic / etiology
  • Blood Cell Count*
  • Diagnosis, Differential
  • Drug-Related Side Effects and Adverse Reactions
  • Erythrocyte Count
  • Erythrocyte Indices*
  • FIGLU Test
  • Folic Acid Deficiency / complications
  • Humans
  • Hypothyroidism / complications
  • Liver Diseases / complications
  • Myeloproliferative Disorders / complications
  • Neural Tube Defects / complications
  • Predictive Value of Tests
  • Reticulocyte Count
  • Risk Factors
  • Sensitivity and Specificity
  • Vitamin B 12 Deficiency / complications