Laboratory investigations for hirsutism
Laboratory investigation to detect biochemical hyperandrogenism (elevated total serum testosterone concentration or elevated free androgen index) is required in all females with hirsutism or other features of PCOS. Measure:
- total serum testosterone concentration—a result more than twice the upper limit of normal requires imaging to exclude androgen-secreting tumours of the ovaries or adrenal glands
- free androgen index (FAI)—this is calculated as total serum testosterone concentration divided by sex hormone–binding globulin (SHBG) concentration, multiplied by 100; it is preferred for diagnosis of biochemical hyperandrogenism because it is more sensitive than total serum testosterone concentration
- serum 17-hydroxyprogesterone concentration (measured during the follicular phase of the menstrual cycle)—elevation during the luteal phase of the menstrual cycle is physiologically normal, but elevation during the follicular phase may indicate nonclassical congenital adrenal hyperplasia
- serum luteinising hormone (LH), estradiol and progesterone concentrations—used to confirm that the individual is in the follicular phase of the menstrual cycle to avoid misinterpretation of serum 17-hydroxyprogesterone concentration
- serum thyroid stimulating hormone (TSH) concentration—hypothyroidism can cause elevated TSH, low SHBG and elevated FAI.
All of the above must be measured in the morning, preferably in the first week of a menstrual cycle, or on any convenient day if the individual is amenorrhoeic1.
Defer testing until at least 3 months have elapsed since any estrogen was taken. Estrogen-containing medications (eg combined hormonal contraception, menopausal hormone therapy) should not be used for at least 3 months before these tests because they elevate serum concentrations of SHBG, which lowers the FAI.
In females with features that may indicate Cushing syndrome (eg central obesity, facial puffiness, peripheral oedema, skin thinning), also consider other diagnostic tests (see Cushing syndrome).