Falsely low parathyroid hormone secondary to biotin interference: a case series

To present a case series on biotin interference in parathyroid hormone (PTH) level measurement.

We review the presentation and management of patients at our institution evaluated for unexpectedly low PTH levels while taking biotin supplements in the setting of high or normal serum calcium.

Two patients presented with surprising low parathyroid levels--one during preoperative evaluation for hyperparathyroidism and another during postoperative follow-up after subtotal parathyroidectomy. The patients were found to be taking 1,500 mcg and 5,000 mcg of biotin per day, respectively. The role of biotin interference was confirmed in one of the patients when she was retested off biotin, and PTH levels responded appropriately. Biotin supplements remain as unbound molecules in the serum, thus interfering with PTH enzyme-linked immunosorbent assay (ELISA) results and falsely depressing the PTH level.

Biotin supplement use has expanded over the years, ranging from medically endorsed therapies to home remedies. Review of the 2 ELISA systems used at our institution demonstrates that free biotin mimics the biotinylated antibody used in the detection process. Screening for biotin use prior to PTH measurement and automatic biotin levels for clinically aberrant PTH levels provide the clinician with a true PTH level--lowering the disease burden of untreated hyperparathyroidism while avoiding unnecessary work-ups for other processes.