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Mili Jain: Key Causes and Diagnosis of Macrocytic Anemia
Mili Jain/ LinkedIn
Aug 27, 2026, 13:39

Mili Jain: Key Causes and Diagnosis of Macrocytic Anemia

Mili Jain, Assistant Professor at Pacific Medical College and Hospital, shared a post on LinkedIn:

” ‘Macrocytic Anemia’

Macrocytic anemia is anemia in which the red blood cells are larger than normal, typically with MCV greater than 100 fL.

Important causes

1. Vitamin B12 deficiency:

  • Pernicious anemia
  • Malabsorption
  • Gastrectomy/bariatric surgery
  • Ileal disease
  • Poor dietary intake
  • Certain drugs, e.g. metformin

2. Folate deficiency:

  • Poor diet/alcoholism
  • Pregnancy
  • Malabsorption
  • Increased requirement
  • Methotrexate and other antifolate drugs

3. Other causes:

  • Alcohol
  • Liver disease
  • Hypothyroidism
  • Myelodysplastic syndrome
  • Reticulocytosis after hemolysis/bleeding
  • Drugs such as hydroxyurea, zidovudine, and some anticonvulsants

Main Classification:

  • ‘Megaloblastic’:– Vitamin B12 deficiency, folate deficiency, drugs affecting DNA synthesis

Key Clues: increased MCV
* Macro-ovalocytes
* Hypersegmented neutrophils, Sometimes leukopenia and thrombocytopenia

  • ‘Non-megaloblastic’:– Alcohol, liver disease, hypothyroidism, reticulocytosis

Key Clues: No typical megaloblastic morphology.

Important PBF findings in Macrocytic Anemia

‘Megaloblastic anemia’ — classic PBF findings:

  • Macro-ovalocytes — most characteristic
  • Hypersegmented neutrophils — 5 or more lobes in a significant proportion of neutrophils, and 1% 6 lobes neutrphil.
  • Anisocytosis and poikilocytosis
  • Oval macrocytes
  • Howell–Jolly bodies, basophilic stippling and may be seen
  • Pancytopenia may occur in severe cases

Useful investigations

CBC, followed by a peripheral blood smear, followed by a reticulocyte count, followed by vitamin B12 and folate testing.

‘Non-megaloblastic macrocytosis’:

  • Round macrocytes/macrocytic RBCs
  • Reticulocytosis may be present
  • Target cells may suggest liver disease
  • No hypersegmented neutrophils.

Depending on the findings:

  • Serum B12
  • Serum/RBC folate
  • Methylmalonic acid (MMA) – increased in B12 deficiency
  • Homocysteine – increased in both B12 and folate deficiency
  • TSH
  • Liver function tests
  • LDH, bilirubin, haptoglobin if hemolysis suspected
  • Consider bone marrow examination if MDS or another marrow disorder is suspected.

B12 vs Folate — high-yield distinction
Finding:

B12 deficiency:

  • MCV , Hypersegmented neutrophils- Present ,increased Homocysteine, increased Methylmalonic acid, Neurological manifestations- Common

Folate deficiency:

  • increased MCV, Hypersegmented neutrophils – Present, increased Homocysteine , Methylmalonic acid- Normal, Neurological manifestations- Usually absent

Macro-ovalocytes and hypersegmented neutrophils: think B12/folate deficiency (megaloblastic anemia).

Important: If B12 deficiency is possible, check B12 before treating with folate alone, because folate can correct the anemia while allowing neurological damage from B12 deficiency to progress.”

Mili Jain: Key Causes and Diagnosis of Macrocytic Anemia

 

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anemia Clinical Hematology Folate Deficiency Hematology Hemostasis News Hemostasis Today Iron-Deficiency medical education Megaloblastic Anemia Mili Jain Peripheral Blood Smear Vitamin B12 Deficiency
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