{"id":"holotranscobalamin","name":"Active Vitamin B12 (Holotranscobalamin)","shortName":"Active B12","aliases":["HoloTC","Holotranscobalamin","Active B12","Holo-TC","Vitamin B12, Active","Holotranscobalamin II","Active Vitamin B12 (Holo-TC)","Holotranscobalamin (Active B12)","Holo-transcobalamin"],"abbreviations":["HoloTC","Holo-TC"],"loinc":[{"code":"72160-5","primary":true}],"specimen":"serum","units":[{"ucum":"pmol/L","display":"pmol/L"}],"referenceRanges":[],"review":{"status":"ai-verified","label":"AI-verified against cited sources. Awaiting expert review","lastReviewed":"2026-10-03"},"summary":"The part of your vitamin B12 that is attached to its carrier protein and ready for your cells to use. It's often called 'active B12'.","url":"https://bloodtesttracker.com/markers/holotranscobalamin","notice":"Information, not medical advice. Ranges differ between labs, so the range on your own report is the one your result is judged against."}