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CPE-009 · Classification
B12-07: Macrocytosis work-up
Macrocytosis work-up. Evaluates MCV above 100 fL.
Condition
- MCV > 100 fL
What it reports
- Macrocytosis has B12 and folate causes and many others: alcohol, liver disease, hypothyroidism, reticulocytosis, myelodysplasia and drugs
Recommended next steps (for physician review)
- Check B12 and folate, a reticulocyte count and a blood film
- Review alcohol, liver and thyroid status and drugs (hydroxyurea, methotrexate, zidovudine, azathioprine)
Diagnostic boundary
- Macrocytosis is absent in many patients with B12 deficiency, especially when iron deficiency coexists.
Evidence
- EV-BSH-2014Devalia V, Hamilton MS, Molloy AM; British Committee for Standards in Haematology. Guidelines for the diagnosis and treatment of cobalamin and folate disorders. Br J Haematol. 2014;166(4):496-513.Supports: Diagnostic approach with serum B12, MMA and homocysteine Neurologic involvement means treatment should not wait for confirmation Folic acid alone must not be given while B12 deficiency is unexcluded
Cases where this rule fires
Open a case to see this rule fire with real inputs, then change the values until it stops.
B12-FX-01
B12 of 150 pg/mL with macrocytic anemia
A 67-year-old with MCV 108.
B12-FX-04
Macrocytic anemia, folic acid ordered, no B12
A safety situation.
B12-FX-06
Posterior-column signs and spasticity
A pattern compatible with subacute combined degeneration.
B12-FX-07
Macrocytosis in a patient with alcohol use disorder
MCV 104, B12 not measured.
B12-FX-08
Low B12 in a 71-year-old with autoimmune thyroid disease and glossitis
Intrinsic-factor antibodies not done.
B12-FX-09
Intrinsic-factor antibodies positive
Pernicious anemia is supported.
B12-FX-10
Hypersegmented neutrophils
MCV 102 and B12 190.
B12-FX-17
Folate 2.8 ng/mL with macrocytosis and alcohol use
B12 is normal.
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