An upsurge in people supplementing with biotin is leading to false results in some immunoassays, writes Giuseppe Barbesino, MD, an assistant professor of medicine at Harvard Medical School, in the December issue of Clinical Laboratory News (CLN). Yet despite at least three published papers on the subject, the medical community remains, by and large, unaware of the issue. 

The water-soluble, B-complex vitamin is a popular over-the-counter supplement for its purported effects in strengthening hair and nails, controlling glucose levels, and easing peripheral neuropathy, Barbesino notes. 

Two characteristics of biotin contribute to the problem. First, biotin easily forms covalent bonds with many small or large molecules without significantly altering their antigenic or biologic properties. Second, the strength of the biotin-streptavidin complex makes it resistant not only to pH and temperature extremes, but also solvents. 

One example is the immunoassay for thyroid stimulating hormone (TSH). The antibody in this test is incubated with the serum sample and a second analyte-specific antibody linked to a reporter system such as ruthenium. The resulting biotinyl-antibody-analyte-ruthenium-antibody complexes normally precipitate on the solid phase coated with streptavidin, with the ruthenium-generated signal directly proportional to the amount of hormone present in the serum sample. 

However, a large excess of soluble biotin in the serum sample competes for streptavidin with the biotin-linked antibody, thus resulting in incomplete or no solid phase formation. This leads to a zero signal, interpreted as a falsely low hormone level.  

In addition, Barbesino continues, biotin excess can also affect competitive assays with the opposite effect, preventing the solid phase formation and yielding a low signal that is interpreted as a falsely high analyte level. 

Recent reports in the literature include patients with Graves’ disease who were misdiagnosed based on falsely low TSH levels; and interference with thyroglobulin, parathyroid hormone, dehydroepiandrosterone sulfate, estradiol, and ferritin assays. 

There are no currently available solutions to the problem, Barbesino concludes. He advises that clinical laboratorians update clinicians on this problem and stress the importance of asking patients about their biotin intake. 

Read more in the December issue of CLN.