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CPE-009 · Context triggers
B12-10: Drug exposure that lowers B12
Drug exposure that lowers B12. Evaluates metformin for 12 months or more, OR proton-pump inhibitor/H2 blocker for 24 months or more, OR nitrous oxide exposure.
Condition
- metformin for 12 months or more, OR proton-pump inhibitor/H2 blocker for 24 months or more, OR nitrous oxide exposure
What it reports
- Drug-associated risk of B12 deficiency
- Nitrous oxide inactivates B12 and can cause neurologic injury with a normal serum level
Recommended next steps (for physician review)
- The ADA standards say periodic B12 measurement should be considered in people on metformin, especially with anemia or neuropathy
Diagnostic boundary
- Exposure raises likelihood; it is not a finding.
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
- EV-STABLER-2013Stabler SP. Vitamin B12 deficiency. N Engl J Med. 2013;368(2):149-160.Supports: Clinical presentations, subacute combined degeneration, nitrous oxide and drug causes
- EV-ADA-STANDARDSAmerican Diabetes Association Professional Practice Committee. Standards of Care in Diabetes, section on pharmacologic approaches to glycemic treatment (current edition). Diabetes Care.Supports: Periodic vitamin B12 measurement should be considered in metformin-treated people, especially those with anemia or peripheral neuropathy
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-05
Neuropathy, B12 220 and metformin for five years
Neurologic features with a borderline level.
B12-FX-11
Metformin for three years, B12 never measured
A screening opportunity.
B12-FX-12
A PPI for 30 months at age 72
Acid suppression and age.
B12-FX-13
Nitrous oxide exposure with neuropathy and a B12 of 310
A normal-looking serum level.
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