💊 Macrocytic Anemia (Elevated MCV) Differential Simulator

Elevated MCV — The First Clue

An MCV over 100 fL on a routine CBC opens the macrocytic differential.

• >100 fL: MCV threshold (placeholder reference range)
• Oval RBCs: Common finding (placeholder smear clue)
• CBC + smear: Initial workup (placeholder first step)
• B12/folate: Next step (placeholder next labs)

Why MCV rises

Placeholder: impaired DNA synthesis enlarges developing red cells.

Megaloblastic Split — B12 or Folate

Serum B12, folate, and methylmalonic acid separate the two megaloblastic paths.

• MMA↑: B12 marker (placeholder specific marker)
• Homocysteine↑: Folate marker (placeholder shared marker)
• B12 only: Neuro signs (placeholder distinguishing clue)
• Folate: Diet clue (placeholder dietary link)

Distinguishing tests

Placeholder: MMA elevated only in B12 deficiency, not folate.

Hypothyroidism as a Non-Megaloblastic Cause

Elevated TSH points toward thyroid-driven macrocytosis without megaloblastic change.

• TSH: Key test (placeholder screening test)
• Slowed turnover: Mechanism (placeholder short mechanism)
• Round macrocytes: Smear finding (placeholder morphology clue)
• Levothyroxine: Treatment (placeholder management)

Thyroid link

Placeholder: hypothyroidism slows red cell maturation, raising MCV.

Alcohol and Liver-Mediated Macrocytosis

Chronic alcohol use and liver dysfunction independently raise MCV.

• GGT↑: Key marker (placeholder liver marker)
• Round macrocytes: Smear finding (placeholder morphology clue)
• Alcohol use: History clue (placeholder history clue)
• Membrane lipid change: Mechanism (placeholder short mechanism)

Alcohol mechanism

Placeholder: alcohol directly toxic to marrow and alters membrane lipids.

Selecting the Confirmatory Test

Final labs confirm the leading candidate before starting treatment.

• MMA + B12: B12 path (placeholder confirm test)
• RBC folate: Folate path (placeholder confirm test)
• Free T4: Thyroid path (placeholder confirm test)
• LFTs + GGT: Liver path (placeholder confirm test)

Final selection

Placeholder: confirmatory test chosen from the highest-likelihood branch.

Placeholder: combine history, labs, and smear to finalize diagnosis.