Which vitamin is known to interfere with some immunoassays when taken in excess?

• A. Biotin (Vitamin B7)
• B. Vitamin C
• C. Vitamin D
• D. Vitamin A

Answer: (A)

Biotin interference is a well-known issue in immunoassays because many assays rely on a biotin-streptavidin system to capture or detect the target. When a patient takes large amounts of biotin, free biotin can saturate streptavidin sites in the assay, blocking the binding of the biotinylated detector reagent. In a typical sandwich immunoassay, this prevents proper signal generation, leading to a falsely low result. The exact effect can vary with the assay design, so some tests may show different directional errors, but the common outcome is erroneous measurements when biotin is consumed in excess. This is why high-dose biotin supplements are a frequent source of misleading immunoassay results, and clinicians often advise stopping such supplements before testing.