B12 Analyzer

B12 levels 200-400 pg/mL are indeterminate. To confirm deficiency, check methylmalonic acid (MMA) — elevated MMA (>0.4 µmol/L) confirms B12 deficiency with high sensitivity. Homocysteine is elevated in both B12 and folate deficiency (less specific). MMA is the preferred confirmatory test. Note: B12 levels can be falsely normal in liver disease, myeloproliferative disorders, and with recent B12 supplementation. Falsely low with oral contraceptives, pregnancy, and HIV.

B12 deficiency can cause irreversible neurological damage even without anemia. Neurological manifestations: subacute combined degeneration (posterior columns + lateral corticospinal tracts), peripheral neuropathy (symmetric, distal, sensory > motor), cognitive impairment, depression, and psychosis. Always check B12 in: unexplained neuropathy, gait ataxia, dementia workup, and psychiatric symptoms in elderly. Treat promptly with IM cyanocobalamin 1000 mcg daily x7 days, then weekly x4, then monthly. Neurological recovery depends on duration of symptoms.

High-risk groups: Pernicious anemia (anti-intrinsic factor antibodies — most common cause in elderly), chronic metformin use (10-30% develop low B12 — screen annually), PPI/H2 blocker use >2 years, prior gastric surgery (sleeve, bypass), ileal resection or Crohn disease, strict vegan/vegetarian diet, chronic alcoholism, and elderly (gastric atrophy reduces absorption). Metformin-induced deficiency is dose-dependent and can be prevented with calcium supplementation.