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CPE-009 · synthetic case B12-FX-26
Methotrexate and a low red-cell folate
A folate-antagonist drug.
Purpose: A folate-antagonist drug.
Inputs the engine received
Laboratory
- Serum vitamin B12
- 410 pg/mL
- Red-cell folate
- 120 ng/mL
- MCV
- 103 fL
Patient
- Age
- 58 years
- Sex
- Female
- Already taking folic acid
- Yes
Drugs, diet and risk groups
- Folate-antagonist drug (methotrexate, trimethoprim, phenytoin)
- Yes
What the engine reports
Detected clinical pattern
Biochemical Pattern Compatible With Folate Deficiency
Folate is low. Check B12 together with folate so a coexisting deficiency is not missed.
- B12 level: B12 410 pg/mL · above 300
Why this pattern was identified
- Supportive context. macrocytosis; folate-antagonist drug are consistent with folate deficiency.
Recommended next steps
For physician consideration. Urgent review always comes first.
- 1Check B12 together with folate, so a coexisting deficiency is not missed.
- 2Check B12 and folate, a reticulocyte count and a blood film; review alcohol, liver and thyroid status and drugs.
Differentials, pitfalls and contradicting signals
- Macrocytosis has many causes beyond B12 and folate: alcohol, liver disease, hypothyroidism, reticulocytosis, myelodysplasia and drugs (hydroxyurea, methotrexate, zidovudine, azathioprine).
Evidence and rule trace · 2 rules
B12-13Low folate
Inputs: red-cell folate 120 ng/mL
Biochemical pattern compatible with folate deficiency.
Evidence
- EV-BSH-2014 · Devalia 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.
- EV-WHO-FOLATE-2015 · World Health Organization. Serum and red blood cell folate concentrations for assessing folate status in populations. Geneva: WHO; 2015.
Physician adjudication required. Clinical decision support for physician review. This output identifies laboratory patterns and safety considerations. It does not diagnose, find the cause, or select a vitamin product, dose or route. Physician adjudication is required.
Change the values
The same engine, starting from this case. Change any value and watch the pattern and the rule trace react.
Serum B12 level
✓ Below 200 pg/mL
Deficiency pattern
✓ 200 to 300 pg/mL
Borderline: MMA and homocysteine settle it
● Above 300 pg/mL
Deficiency unlikely, not excluded
Laboratory
- <200
- 200–300
- >300
Patient
Neurologic features
Drugs, diet and risk groups
More b12 cases
B12-FX-01
B12 of 150 pg/mL with macrocytic anemia
A 67-year-old with MCV 108.
B12-FX-02
Borderline B12 with raised MMA
B12 260 and MMA 0.52.
B12-FX-03
Borderline B12 and no confirmatory test
B12 250.
B12-FX-04
Macrocytic anemia, folic acid ordered, no B12
A safety situation.
B12-FX-05
Neuropathy, B12 220 and metformin for five years
Neurologic features with a borderline level.
B12-FX-06
Posterior-column signs and spasticity
A pattern compatible with subacute combined degeneration.
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