The preferred sample for the standardized measurement of FSH and LH is serum obtained from whole blood collected in a fasting state. FSH and LH are also excreted in the urine. Rapid testing methods and point-of-care devices have been developed for urine FSH and LH and are used to predict ovulation or as indicators for the onset of menopause.
In clinical laboratories, the gonadotropins are most commonly measured in serum using immunoassay methods that employ chemiluminescent detection. Antibodies used in these immunoassays must have specificity for regions on the beta subunit to eliminate cross-reactivity with other hormones that share the same alpha subunit, such as TSH and hCG, and to differentiate between FSH and LH.
Historically, immunoassay methods employing radioisotopes were used to measure the gonadotropins. These previous generation assays had higher detection limits than today's immunoassays and could not readily distinguish between frank deficiencies and adequate hormone levels.
Chromatographic methods for the gonadotropins have been developed, although their use is fairly limited to reference laboratories, particularly when interferents are encountered with immunoassay methods.
