Contents:
- What is the difference between a serum test and a holo TC test?
- How accurate are the results of a holo TC test?
- How expensive are they?
- Is it possible to conduct a holo TC test at home?
Holo TC Test vs Vitamin B12 Serum Test (Total Vitamin B12)
Most people who want to take a vitamin B12 test are prescribed a serum test by their doctor, which measures the total B12 content in the blood. This is despite numerous studies over the last 10 years, which have exposed their inaccuracy (1, 2). The main problem with serum tests is that they usually measure both B12 that is unavailable to the body because it is bound to protein (haptocorrine), as well as certain chemical substances that, although similar to the vitamin, are biologically useless – known as B12 analogues. Furthermore, as control studies have shown, the laboratory methods used also appear to be prone to errors (3).
Holo TC Tests for an Exact Vitamin B12 Status
The body can only utilise vitamin B12 that is bound to a special transport molecule, known as transcobalamin (TC). It is this TC-bound B12 that is measures by the holotranscobalamin (holo TC) test. The significance of this quickly becomes clear if you considers that only 6-25% of the total B12 content is bound to transcobalamin and thus biologically available. Consequently, serum tests measure up to 80% of the unavailable vitamin; whereas holo TC tests give much more accurate information on the status of available B12 (4).
The Earliest Indication of Vitamin B12 Deficiency
Even when vitamin B12 deficiency has set it, many types of B12 test will still produce seemingly normal results. In contrast, the holo TC test can recognise deficiency already in its earliest stages, making it the most sensitive test available. Plus, there are almost no other biological factors that can interfere with its results, making it very reliable. Only a reduced production of TC transport molecules due to hereditary diseases, for example, can affect a holo TC test. As a result, it is a wonder why this test has not yet become a medical standard (5).
Waiting Period Before a Holo TC Test
No vitamin B12 supplements should be taken for 10 days leading up to a holo TC test, in order to prevent false results and better measure the current condition of the body’s vitamin B12 store.
Holo TC Test Evaluation
Here are the common evaluations of holo TC test results:
| Value | Interpretation |
| < 35 pmol/l | B12 deficiency |
| 35 – 50 pmol/l | Grey area, deficiency or undersupply |
| > 50 pmol/l | Good B12 supply |
Already with the onset of an undersupply and a depletion of the body’s store, the holo TC value begins to sink below 50 pmol/l and therefore reliably shows the beginnings of a deficiency.
Holo TC Test Cost
A holotranscobalamin test can be performed either by a doctor/naturopath or independently at home. In both cases a blood sample is required. In the self-test only a few drops of blood are sufficient, taken from the fingertip by means of a small, painless needle.
Special needles are included within test kits. The blood is then sent to a professional laboratory – just like a sample taken by the doctor. Home test kits are available from around £39/$49.
Holo TC in Combination with Other Tests
The holo TC test reliably shows how much B12 the body has available. Yet what it does not reveal is whether the available B12 can be correctly utlised by the body. This is only possible though a metabolite test, which measures special degradation products in the body, the concentration of which depends on B12. There are two metabolites that are relevant to vitamin B12: homocysteine, which increases with a deficiency of methylcobalamin or folic acid, and is therefore relatively inaccurate; and MMA, which increases with a deficiency of adenosylcobalamin and is dependent only on cofactors such as biotin, considered to be fairly accurate. Neurologists in particular sometimes prefer to perform all available tests in order to arrive at an interpretation of the overall picture. This makes sense, but is quite expensive. For those who only want to test their vitamin B12 supply for reasons such as veganism and vegetarianism, a holo TC test will usually suffice. In the case of special clinical pictures, however, a more precise evaluation through combined tests can sometimes provide important detailed information.
Conclusion: Holo TC Test
It is highly likely that the holotranscobalamin or holo TC test will establish itself as the most effective vitamin B12 test in the near future; its great sensitivity and accuracy make it a first-class diagnostic tool. While the test still remains relatively unknown, hopefully its popularity will grow due to the home test kits now available.
Sources
- Herrmann, Wolfgang; Obeid, Rima; Schorr, Heike; Geisel, Jurgen. The Usefulness of Holotranscobalamin in Predicting Vitamin B12 Status in Different Clinical Settings. Current Drug Metabolism, Volume 6, Number 1, February 2005, pp. 47-53(7)
- Herbert, V., Fong, W., Gulle, V. and Stopler, T. (1990), Low holotranscobalamin II is the earliest serum marker for subnormal vitamin B12 (cobalamin) absorption in patients with AIDS. Am. J. Hematol., 34: 132–139. doi: 10.1002/ajh.2830340210
- Carmel, Ralph; Agrawal, Yash Pal. Failures of cobalamin assays in pernicious anemia. New England Journal of Medicine, 2012, 367. Jg., Nr. 4, S. 385-386.
- Nexo E, Hoffmann-Lücke E. Holotranscobalamin, a marker of vitamin B-12 status: analytical aspects and clinical utility. Am J Clin Nutr. 2011 Jul;94(1):359S-365S. doi: 10.3945/ajcn.111.013458. Epub 2011 May 18. Review. PubMed PMID: 21593496
- HVAS, A.-M. and NEXO, E. (2005), Holotranscobalamin – a first choice assay for diagnosing early vitamin B12 deficiency?. Journal of Internal Medicine, 257: 289–298.
