There it is, sitting next to your toothbrush: a little bottle promising healthier-looking hair and stronger nails. You take a capsule with breakfast, head off for a routine blood test and think nothing more of it. But what if something in that supplement could influence the result your doctor receives? Some beauty products contain high doses of biotin, a vitamin that can interfere with certain laboratory tests. The surprising part is that the supplement may affect the measurement without changing what is actually happening inside your body. On this page What Is Biotin and Why Is It in Beauty Supplements? How Can a Vitamin Interfere With a Laboratory Test? Which Blood Tests May Be Affected? Does Every Supplement Cause the Same Problem? What Should You Tell Your GP or Laboratory? Should You Stop Your Supplement Before a Blood Test? When Medical Asse...