A Holotranscobalamin blood test measures the fraction of vitamin B12 bound to transcobalamin (holotranscobalamin or holoTC), the biologically active form available to cells. It can detect B12 deficiency earlier than total B12, assess tissue B12 availability, and is used when deficiency is suspected (anemia, neuropathy) or to monitor supplementation. Low holoTC suggests inadequate B12 and may prompt further evaluation.

Vitamin B12 (cobalamin) refers to the total vitamin measured in blood, including B12 bound to haptocorrin (largely inactive) and transcobalamin. Holotranscobalamin (holoTC) is the small fraction of B12 bound to transcobalamin that’s delivered to cells — the biologically active form. HoloTC better reflects bioavailable B12 and can reveal deficiency earlier than total B12 measurements.

The active B12 (holotranscobalamin) test typically costs about $25–$200 in the US, £40–£120 privately in the UK, and ₹600–₹2,000 in India, depending on the laboratory, location, and whether public healthcare covers it. Prices vary widely between hospitals, private labs and online booking platforms, so check local lab listings or call diagnostic centers for up-to-date exact pricing.

Treat low holotranscobalamin by correcting B12 deficiency: start replacement (high‑dose oral cyanocobalamin or methylcobalamin 1,000–2,000 mcg daily if absorption is adequate; intramuscular B12 1,000 mcg weekly for several weeks, then monthly for severe deficiency or malabsorption). Identify and treat underlying causes (pernicious anemia, medications, surgery), monitor B12, blood counts and neurologic symptoms, and supplement folate if needed.

Normal serum vitamin B12 is generally 200–900 pg/mL (≈148–664 pmol/L). Holotranscobalamin (active B12) is more sensitive: levels below ~35 pmol/L are considered low and suggest early B12 deficiency (some labs use <20 pmol/L for definite deficiency). Low holoTC often prompts follow-up tests such as methylmalonic acid or homocysteine, or treatment.

B12 deficiency commonly causes fatigue, weakness, pale or jaundiced skin, shortness of breath and dizziness. Neurological signs include numbness or tingling in hands and feet, balance and coordination problems, memory loss, confusion, mood changes or depression, and vision disturbances. Other features can be sore red tongue, mouth ulcers, appetite and weight loss, and gastrointestinal upset; untreated deficiency may cause anemia and nerve damage.