Extremely high follicle-stimulating hormone with normal ovarian function.

The work-up for a discrepant immunoassay result is challenging. A 34-year-old woman with normal menstruation and ovarian function had high follicle-stimulating hormone (FSH) around 100-200 IU/L by Roche elecsys e602 (reference interval 3.0-14.0 IU/L). Magnetic resonance imaging excluded pituitary tumors. A dilution study indicated an interference, however, a heterophilic antibody was not identified. After IgG depletion by protein A/G resin, the FSH recovery was 26% and FSH concentration dropped to 20.2 IU/L. This rare macro-FSH case should be brought to the attention of clinical laboratorians, obstetrician-gynecologists, and reproductive endocrinologists.