ELISA tests

BIOHIT Active B12 test (HoloTC)

An accurate test for measuring the levels of active vitamin B12

The traditional method of diagnosing vitamin B12 deficiency has been to measure the concentration of total vitamin-B12 in the serum. The total vitamin B12 concentration essentially reflects vitamin-B12 which is bound to its two carrier proteins forming, holohaptocorrin (holoHC) and holotranscobalamin (holoTC). Whilst holoHC accounts for 70 % – 80 % of the vitamin B12 in serum, only holoTC (active vitamin B12) can be used by human cells. Measurement of total vitamin B12 can hence give erroneous results because it measures the vitamin B12 which is in circulation but does not indicate the active vitamin B12 that is available to the cells of the body.

BIOHIT Active B12 (HoloTC) test provides a solution to this diagnostic paradox: this test directly measures holoTC – the biochemically active form of vitamin B12 – from the human serum. This test is well suited for the screening of patients with a suspected vitamin B12 deficiency. BIOHIT Active B12 test can also be used for confirming the vitamin B12 status in the large number of patients who get an inconclusive result from total vitamin B12 tests.

Product specifications of the Active B12 test

  • Measures the concentration of active vitamin B12 (holotranscobalamin) available to the cells
  • Proven ELISA technology, support for both automated and manual analysis methods
  • Unlike total B12 kits, no issues with Intrinsic Factor Blocking Antibody (IFBA) interferences
  • Numerous clinical studies proving the performance of Active vitamin B12 over total B12


Understanding the role of active B12 testing

Three binding proteins are involved in the transport of vitamin B12 around the body – Intrinsic Factor (IF), transcobalamin (TC) and haptocorrin (HC). These binding proteins ensure the efficient uptake of the very small amounts of vitamin B12 available from the diet. When TC and HC bind vitamin B12 the resulting complexes are known as holotranscobalamin (HoloTC) and holohaptocorrin (HoloHC) to distinguish them from the proteins carrying no vitamin.

The major fraction in the circulation, HoloHC, represents 70-90 % of vitamin B12 in the blood but is biologically inert. HoloTC represents only 10-30 % of vitamin B12 circulating in the blood but is the only form of vitamin B12 that can be taken up by cells in the body. The TC protein alone transports vitamin B12 from its site of absorption in the ileum to tissues and cells. The vitamin is then internalised as the HoloTC (vitamin B12 bound to transcobalamin) complex via a specific receptor-mediated uptake. This process delivers vitamin B12 into the cells of the body and provides the vitamin as a co-enzyme for essential cellular functions such as DNA synthesis. As HoloTC has a shorter circulating half-life compared to HoloHC the earliest change that occurs on entering negative vitamin B12 balance is very likely to be a decrease in serum HoloTC concentration.

The measurement of Total Serum B12 suffers from some limitations; in particular, most of the measured cobalamin is bound to biologically inert HC. Several studies have been published which conclude that HoloTC would be a better indicator of vitamin B12 status than Total Serum B12. As expected, HoloTC levels are low in patients with biochemical signs of vitamin B12 deficiency. Low values have been reported in vegetarians, vegans, and in populations with a low intake of vitamin B12. Notably, low levels of HoloTC but not Total B12 in serum were reported in patients with Alzheimer’s disease compared to levels in a healthy control group. Tested HoloTC levels reflect vitamin B12 status, independent of recent absorption of the vitamin.


602290BIOHIT Active B12 (HoloTC)96 wells


Instructions for use

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