Initial hormonal investigation should aim at excluding disorders of hypothalmic-pituitary-ovarian axis that cause ovulation disturbance. Measurements should ideally occur in the first week of the menstrual cycle and include:
- testosterone, sex binding globulin, FSH, LH, PRL, TFTs
A diagnosis of PCOS is supported by:
- elevated free testosterone levels (in saliva or plasma)
- low levels of sex hormone binding globulin
- to calculate the free androgen index (FAI), total testosterone value x 100 is divided by the sex hormone binding globulin value (1)
- FAI levels of 5 and above are indicative for polycystic ovary syndrome (2)
- other disorders presenting with clinical and/or biochemical signs of hyperandrogenism such as congenital adrenal hyperplasia, androgen-secreting tumours or Cushing syndrome should be excluded. For this purpose further laboratory testing, e.g. 17-OH-progesterone, follicle-stimulating hormone, oestradiol, prolactin or cortisol may be necessary
- elevated LH:FSH ratio - usually, to more than 3:1; serum LH is raised with that of FSH relatively lower than in a normal menstrual cycle; measure in the first week of the menstrual cycle
- however, an elevated LH:FSH ratio is no longer considered to be a diagnostic criterion for PCOS due to its inconsistency (1)
- there may also be elevated androstenedione levels and high circulating levels of oestrone
Note that serum testosterone levels in patients with PCOS seldom exceed 4.8 nmol/l. If testosterone levels are greater than 4.8 nmol/l then further endocrinological investigation to exclude other causes of androgen hypersecretion (e.g. Cushing's syndrome, adrenal gland or ovarian tumours) (3).
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