PCOS affects 1 in 10 women — but many spend years without a clear diagnosis. Here's exactly what to test and what it means.
Polycystic ovary syndrome (PCOS) affects approximately 1 in 10 women of reproductive age in the UK. Despite being so common, the average time from first symptoms to diagnosis is still over 2 years. Many women spend years being told their periods are "just irregular" or their acne is "hormonal" without anyone investigating the underlying cause.
Getting the right blood tests is a critical step towards diagnosis — but knowing which tests to ask for, and understanding what the results actually mean, is not always straightforward. This guide explains the full PCOS blood panel and what each result tells you.
PCOS is diagnosed using the Rotterdam criteria, which require at least 2 of the following 3 features:
Irregular or absent periods (oligomenorrhoea or amenorrhoea)
Clinical or biochemical signs of androgen excess (acne, excess hair, raised testosterone)
Polycystic ovaries on ultrasound (≥20 follicles per ovary, or increased ovarian volume)
This means blood tests alone cannot confirm PCOS. But they are an essential part of the picture — and they can rule out other conditions that mimic PCOS (such as thyroid disease, hyperprolactinaemia, or non-classic congenital adrenal hyperplasia).
At Lambert Medical Practice in Surbiton, our diagnostic centre processes all of the following in a single blood draw:
| Test | What it measures | PCOS findings |
|---|---|---|
| LH (Luteinising Hormone) | Pituitary hormone that triggers ovulation | Often elevated in PCOS; classic LH:FSH ratio >2:1 |
| FSH (Follicle-Stimulating Hormone) | Stimulates follicle development | Usually normal or slightly low in PCOS |
| Total testosterone | Androgen (male hormone) produced in ovaries and adrenals | Elevated in ~60–80% of PCOS cases |
| Free testosterone / FAI | Testosterone available to tissues (adjusted for SHBG) | More sensitive indicator than total testosterone alone |
| SHBG (Sex Hormone-Binding Globulin) | Protein that binds testosterone and oestrogen | Often low in PCOS — amplifies effect of testosterone |
| AMH (Anti-Müllerian Hormone) | Reflects ovarian follicle reserve | Elevated in PCOS (3–4× normal); useful diagnostic marker |
| Oestradiol | Main oestrogen; reflects follicular activity | Often normal in PCOS; low if amenorrhoeic |
| Prolactin | Pituitary hormone; elevated levels suppress ovulation | Mildly elevated in PCOS; must rule out prolactinoma |
| TSH (Thyroid) | Thyroid function; affects menstrual regularity | Thyroid disease mimics PCOS — must be excluded |
| Fasting insulin & glucose | Insulin sensitivity | Insulin resistance present in ~70% of PCOS cases |
| HbA1c | 3-month average blood glucose | Elevated if insulin resistance has progressed to pre-diabetes |
| Fasting lipids | Cholesterol, triglycerides | PCOS associated with dyslipidaemia |
A classic PCOS finding is an LH:FSH ratio greater than 2:1 — sometimes written as 3:1. This reflects the abnormal pulsatile gonadotrophin secretion that disrupts follicle development. However, the LH:FSH ratio is not part of the Rotterdam diagnostic criteria and is not elevated in all women with PCOS. It is suggestive but not confirmatory.
Total testosterone may be in the "normal" range even when there is functional androgen excess — because SHBG (which binds testosterone and inactivates it) is often low in PCOS. When SHBG is low, more testosterone is biologically active, causing symptoms like acne, hirsutism (unwanted hair), and hair thinning, even when the total figure looks acceptable. The free androgen index (FAI = total testosterone ÷ SHBG × 100) is a more sensitive marker.
Anti-Müllerian Hormone (AMH) is produced by ovarian follicles. Women with PCOS typically have significantly elevated AMH — often 3–4 times the upper limit of normal — reflecting the high number of small antral follicles that characterise polycystic ovaries. AMH is now considered one of the most reliable markers for PCOS diagnosis, particularly when ultrasound is not available or inconclusive.
Around 70% of women with PCOS have insulin resistance — the cells do not respond efficiently to insulin, so the pancreas produces more. Elevated insulin stimulates the ovaries to produce additional testosterone, worsening the hormonal imbalance. Fasting insulin with a fasting glucose ratio (HOMA-IR) is the most practical clinical measure. Elevated HbA1c suggests the insulin resistance has progressed further.
Identifying insulin resistance changes management significantly — lifestyle interventions (reducing refined carbohydrate, increasing exercise) are particularly effective, and metformin may be appropriate in some cases.
At Lambert Medical Practice, blood results are reviewed with Dr Dela at a follow-up appointment (or via phone/video). She explains each result in plain language and places it in the context of your symptoms and clinical examination.
If the blood tests suggest PCOS, next steps typically include:
Full hormone panel · Same-day results available · Dr Dela Dillon-Gbekor · No referral needed