The alarming hormone results were the test, not the hormones
In 23 samples from people on high-dose biotin, most of ten hormones read abnormal. Removing the biotin from the sample returned them to normal, and biotin-free assays read normal.
What the study found
Strip the biotin out and the abnormal hormone results go away
In 23 plasma samples from people on high-dose biotin, most of ten measured hormones read abnormal. A procedure that removes biotin from the sample returned them to normal, and assays that do not use biotin capture read normal throughout. The hormones were never the problem.
The caveat · Doses far above any hair supplement
23 samples, and the exposure is multiple sclerosis treatment at doses far above any hair supplement, so the blood levels here are an upper bound rather than what a shopper reaches. Two authors worked for the company developing that high-dose product, which had a commercial interest in characterising this interference. Roche assays only, and the removal step is not perfectly neutral: it shifts parathyroid hormone by about 8%.