Holotranscobalamin (holoTC), også kjent som aktivt vitamin B12, er en form for vitamin B12 som er bundet til transcobalamin, et transportprotein i blodet. Denne kombinasjonen er biologisk betydningsfull fordi det er den eneste formen for vitamin B12 som kan tas opp av celler via reseptormediert endocytose, noe som gjør den lett tilgjengelig for cellulære prosesser. Måling av holotranscobalamin-nivåer anses å være en mer direkte markør på kroppens nylige vitamin B12-status enn total vitamin B12-test, da den representerer den fraksjonen av vitamin B12 som faktisk er tilgjengelig for opptak i cellene og umiddelbar bruk.
Individuals who are at risk of vitamin B12 deficiency, such as vegetarians, elderly people, and those with absorption impairments like pernicious anemia or gastrointestinal disorders, would benefit from testing their holotranscobalamin levels. It helps in early detection and management of deficiency.
Symptoms of low holotranscobalamin, indicating vitamin B12 deficiency, include fatigue, weakness, memory loss, neurological and psychiatric problems, and anemia. These symptoms result from the impaired production of DNA and red blood cells and neurological function.
Holotranscobalamin testing measures only the biologically active portion of vitamin B12 available for cellular uptake, providing a more accurate reflection of functional vitamin B12 status. In contrast, total vitamin B12 testing measures all forms of B12, including those that are not immediately available to cells, which can sometimes mask deficiencies.
Low holotranscobalamin levels are primarily caused by dietary inadequacy, malabsorption syndromes, pernicious anemia, certain medications, and age-related decline in absorption. These factors lead to insufficient availability of biologically active vitamin B12.