PCOS: which markers are involved

PCOS is diagnosed by criteria, not by a single test — and the blood markers involved each cover one corner of a three-cornered definition.

How the diagnosis is actually built

Polycystic ovary syndrome is diagnosed clinically, on a combination of features: irregular or absent ovulation, evidence of higher androgen activity — clinical or biochemical — and characteristic ovarian appearance on ultrasound. No blood result diagnoses it alone; the markers below supply the biochemical corner and rule out conditions that mimic it. Assembling the picture is a doctor's job, usually a GP's to start.

The androgen markers

Total testosterone is the anchor — modestly raised in many women with PCOS. SHBG is measured with it, and tends to run low, partly because the insulin resistance that often travels with PCOS suppresses it. The two combine into the free androgen index, which frequently shows the picture more clearly than either alone: modest testosterone over low SHBG means more active androgen than the total suggests.

The supporting cast

LH and FSH — LH often runs high relative to FSH in PCOS. The ratio is a supporting clue, present in many and absent in plenty, so it contributes without deciding.

AMH — typically well above age-expected levels, reflecting the higher count of small follicles. It supports the picture and is not diagnostic alone.

The exclusions — thyroid function and prolactin are checked because thyroid dysfunction and raised prolactin both disrupt cycles and can impersonate parts of the syndrome. Ruling the mimics out is as much a part of the workup as ruling PCOS in.

The metabolic half

PCOS is not only reproductive. Insulin resistance is common within it, which is why assessment usually includes glucose, HbA1c and lipids — and why those markers remain worth watching long-term for anyone diagnosed. This is the half of the condition that blood testing monitors best, and the half most responsive to the ordinary levers of activity and weight management, guided by a doctor.

What these markers won't tell you

• No marker diagnoses PCOS. The diagnosis is criteria-based and clinical — results contribute, symptoms and ultrasound complete it.
• Normal results don't exclude it. Biochemical androgen excess is one route to the diagnosis, not a requirement.
• Timing still rules. Cycle-dependent markers need the right day and hormonal contraception changes several of them — testing context matters.
• Management is individual. What follows a diagnosis depends on goals — cycles, fertility, metabolic health, skin — and that plan is built with a doctor, not a panel.

The bottom line

The blood work in PCOS does three jobs: measures androgen activity properly — testosterone with SHBG, not alone — rules out the impersonators, and maps the metabolic side. The syndrome itself is diagnosed by a clinician assembling all three corners, and managed as the long-term, whole-of-health condition it is.