Vitamin B12 — pg/mL to pmol/L

In short To convert vitamin B12 from pg/mL to pmol/L, multiply by 0.737809 — so one pg/mL is 0.737809 pmol/L, and one pmol/L is 1.35536 pg/mL. 200 pg/mL is 148 pmol/L; 300 pg/mL is 221 pmol/L; 500 pg/mL is 369 pmol/L. The factor comes from the molar mass, because cyanocobalamin has a molar mass of 1355.4 g/mol — by far the largest on this page; that is why it differs for every analyte and why a single "lab unit converter" factor does not exist. B12 is a very large molecule, so the numbers in the two systems are closer together than for most analytes — the factor is 0.738, not a factor of ten or a thousand — and that closeness is the trap. A result of 250 could plausibly be either unit, and unlike creatinine or vitamin D there is no obvious tell. This converts units. It does not interpret results, does not compare your value against a reference interval, and is not a substitute for the clinician who ordered the test — reference intervals differ between laboratories, methods and populations.