Diagnosing Low Testosterone
How are low testosterone levels diagnosed?
If a physician suspects low testosterone based on symptoms and physical examination, the diagnosis must be confirmed by laboratory testing.
Most circulating testosterone is bound to sex hormone-binding globulin and albumin. In young adult men, only about 2 percent of testosterone is unbound (free testosterone). Total testosterone (bound plus free testosterone) is the preferred measure since tests for free-testosterone are not as accurate.
Testosterone levels are best measured early in the morning. This is because testosterone level has a daily pattern (diurnal) where it is most abundant at about 8:00 a.m.
Testing of LH and FSH, other hormones that stimulate the testes, are also performed to determine whether the cause of low testosterone is primary or secondary.
