Polycystic ovarian syndrome

The diagnosis of PCOS requires confirmation of ovarian dysfunction: irregular or anovulatory cycles, or polycystic morphology on scanning; and androgen excess: either clinical or biochemical.

Baseline investigations - all patients

Full blood count

Useful indicator of general health and underlying disease. Menorrhagia may cause microcytic anaemia, and exacerbate hair loss.

Urea and electrolytes

Hypokalaemia may raise the possibility of cortisol excess.

Liver function test

Useful indicator of general health and underlying disease.

Fatty liver is common in both obesity and diabetes. It's also needed as a baseline before starting medical treatments.

Bone profile

Useful indicator of general health and underlying disease.

Thyroid stimulating hormone

Unrecognised hypothyroidism is associated with weight gain and menstrual disturbance.


Hyperprolactinaemia of any cause is associated with oligomenorrhoea. 

Mild degrees of hyperprolactinaemia are also seen in PCOS and may not indicate pituitary or other pathology.

Fasting glucose and lipids

Essential for cardiovascular risk stratification.

Testosterone, sex hormone binding globulin

This should be performed early morning, early follicular phase and off the contraceptive pill. 

Sex hormone binding globulin is typically low in PCOS and Cushing’s. Testosterone is typically but not always mildly elevated in PCOS. High levels (>3.5nmol/l in the author's institution) should prompt a search for other causes, for example virilising tumours or Cushing’s syndrome.

Further investigations - selected cases only

Luteinising hormone, follicle stimulating hormone

Elevated luteinising hormone: follicle stimulating hormone ratio is often seen in PCOS but is not diagnostic and so is not necessarily performed in all cases.

LH and FSH may both be low in pituitary and hypothalamic causes of oligomenorrhoea, for example associated with low body mass or anorexia or excessive exercise. FSH will be elevated in the secondary amenorrhoea of premature ovarian failure.

170H progesterone

This test needs to be performed early morning, early follicular phase and off the contraceptive pill. 

17OHP is a useful initial screen for congenital adrenal hyperplasia - if elevated above 10nmol/l, the patient will require full evaluation: a short synacthen test.


This should be taken on day 21 of the menstrual cycle to indicate ovulation in patients with regular menses and diagnostic uncertainty.

This should also be recorded in patients seeking fertility.

Androstenedione, dihydoepiandrosterone

In virilised patients, those with elevated testosterone, or suspected Cushing’s syndrome, or other adrenal pathology, full adrenal androgens should be assessed. These are typically minimally elevated in PCOS, higher in Cushing’s and adrenal tumours. 

2x24hr urinary free cortisols

Urinary cortsiols form a sensitive but not specific initial screen if Cushing's syndrome is suspected.

Low dose dexamethasone suppression test

If there is a clinical suspicion of Cushing’s syndrome, a low dose dexamethasone suppression test (LDDST) should be performed to seek suppressibility of cortisol.

If androgens are elevated, LDDST should also be performed. Suppressibility of adrenal androgens by more than 40% has been reported as making virilising tumours highly unlikely.

Short synacthen test

If the baseline 17 hydroxyprogesterone is elevated >10nmol/l, proceed to a synacthen test to confirm or exclude late onset congenital adrenal hyperplasia.

CT adrenals

If adrenal androgens are elevated, and do not suppress after dexamethasone testing, a virilising tumour should be suspected and CT or MRI imaging should be peformed.

Selective venous sampling of adrenals and ovaries

If androgens are elevated and do not suppress after dexamethasone, imaging of the ovaries and adrenals should be arranged. If no obvious lesion is revealed on imaging, selective venous sampling of the abdomen and pelvis may identify the source of androgens.

Transvaginal ovarian ultrasound scan

This may be useful in cases of diagnostic difficulty where there is evidence of hyperandrogenism but not of ovarian dysfunction.

Typical polycystic appearance is supportive but not diagnostic of PCOS, as it may also be observed in many other conditions for example acromegaly, Cushing's syndrome and many normal women.

Ovarian imaging (by ultrasound or MRI) is also mandatory where there is a suspicion of virilising tumour.

MRI pelvis and adrenals

When a virilising tumour is strongly suspected but not visualised on ultrasound scan, MRI pelvis may be helpful and can be combined with adrenal imaging to avoid the abdominal radiation exposure necessary for an adrenal protocol CT scan in a young woman.