PCOS Blood Test: Which Markers Confirm a Diagnosis

Polycystic ovary syndrome (PCOS) affects roughly 1 in 10 women of reproductive age in the UK — that's about 3.5 million women. Despite being one of the most common endocrine disorders, it takes an average of 2 years and visits to 3 or more clinicians before most women receive a diagnosis. Part of the problem is that GPs often order incomplete blood tests that miss the full picture.

How PCOS Is Diagnosed: The Rotterdam Criteria

The internationally accepted Rotterdam criteria require at least 2 of the following 3 for a PCOS diagnosis:

1. Irregular or absent periods (oligo-ovulation or anovulation)
2. Clinical or biochemical signs of elevated androgens (acne, hirsutism, hair thinning, or raised testosterone/DHEA-S on blood tests)
3. Polycystic ovaries on ultrasound (12+ follicles per ovary, or ovarian volume above 10 ml)

Blood tests are essential for the androgen component — and they're also the only way to properly assess the metabolic risks that come with PCOS, which many GPs neglect entirely.

The Blood Markers You Actually Need

Androgen Panel

This is the core of a PCOS blood test. Many GPs test only total testosterone, which is a starting point but frequently misses the diagnosis. Here's what a complete androgen assessment should include:

• Total testosterone — the headline androgen marker; elevated above 1.7 nmol/L in women raises suspicion for PCOS
• Free testosterone — the biologically active fraction; more sensitive than total testosterone for detecting hyperandrogenism. Can be elevated even when total testosterone is normal
• SHBG (sex hormone-binding globulin) — a binding protein that controls how much testosterone is "free" and active. SHBG is frequently low in PCOS, which means more free androgens circulating even if total testosterone looks acceptable. Low SHBG is also linked to insulin resistance
• DHEA-S (dehydroepiandrosterone sulphate) — an adrenal androgen; elevated in about 20-30% of women with PCOS. Helps distinguish ovarian from adrenal androgen excess
• Androstenedione — a precursor to testosterone; can be elevated in PCOS even when testosterone is borderline

LH and FSH — The Ratio That Matters

In a normal menstrual cycle, LH and FSH are roughly equal in the early follicular phase (days 2-5). In PCOS, LH is often disproportionately elevated relative to FSH.

• LH:FSH ratio above 2:1 is suggestive of PCOS (though not required for diagnosis)
• Why it happens: the hypothalamus increases GnRH pulse frequency in PCOS, which preferentially stimulates LH release over FSH
• Important note: this ratio is only useful when tested on days 2-5 of the cycle. Later in the cycle, LH naturally surges and the ratio becomes meaningless

About 60% of women with PCOS show an elevated LH:FSH ratio, so a normal ratio doesn't rule it out — but an abnormal ratio adds supporting evidence.

Metabolic and Insulin Resistance Markers

This is where most GP assessments fall short. PCOS is fundamentally a metabolic condition for many women — insulin resistance drives the excess androgen production in 70-80% of cases. Yet insulin resistance testing is routinely overlooked.

• HbA1c — measures average blood sugar over 2-3 months. Normal below 42 mmol/mol, pre-diabetic 42-47 mmol/mol. Women with PCOS have a 4-7 times higher risk of developing type 2 diabetes
• Fasting insulin — a more sensitive marker of insulin resistance than HbA1c alone, especially in younger women. Elevated fasting insulin (above 10-12 mU/L) suggests the pancreas is working overtime to keep blood sugar normal
• Lipid panel — PCOS is associated with elevated triglycerides, low HDL, and raised LDL. Cardiovascular risk assessment should be part of every PCOS workup

Rule-Out Markers

Several other conditions can mimic PCOS, and your blood test should help exclude them:

• TSH (thyroid) — hypothyroidism can cause irregular periods and weight gain; always check thyroid function when PCOS is suspected
• Prolactin — elevated prolactin (from a pituitary adenoma or medication) can cause menstrual irregularity and mild androgen excess. Prolactin above 1000 mU/L needs further investigation
• 17-hydroxyprogesterone — screens for late-onset congenital adrenal hyperplasia (CAH), which presents identically to PCOS but is a different condition entirely. Often missed if not specifically requested

When to Test

• Days 2-5 of your cycle — this is essential for accurate FSH, LH, oestradiol, and testosterone readings
• If you don't have regular periods — test any day, but note this on your results so your clinician can interpret them correctly
• Fasting — if your panel includes insulin or a lipid profile, fast for 10-12 hours beforehand (water is fine)

Understanding Insulin Resistance in PCOS

Insulin resistance is the metabolic engine behind most cases of PCOS. Here's how the cycle works: excess insulin stimulates the ovaries to produce more testosterone. That excess testosterone disrupts follicle development (causing the "cysts" on ultrasound), blocks ovulation, and triggers symptoms like acne and excess hair growth.

Addressing insulin resistance — through diet modification, exercise, weight management, or medications like metformin — often improves androgen levels and restores ovulation without needing to treat the hormones directly. This is why metabolic markers are not optional extras in a PCOS blood test — they're central to understanding your specific type of PCOS and choosing the right treatment approach.

Which Lola Health Test Should You Choose?

The PCOS Clarity 24 test (£143) was specifically designed for investigating PCOS. It includes a full androgen panel (testosterone, free testosterone, SHBG, DHEA-S, androstenedione), LH, FSH, prolactin, thyroid function, HbA1c, and a lipid profile. It's the single most complete PCOS blood test panel available in the UK for at-home testing.

If you're looking for a broader hormone assessment that also covers thyroid and cardiovascular markers, the Female Hormones Clarity 31 test (£115) is a strong alternative that includes many of the same markers plus additional thyroid and vitamin tests.

Stop Waiting for a Diagnosis That's Already Late

Two years is too long to wait for answers about your body. If you're experiencing irregular periods, acne, excess hair growth, hair thinning, difficulty losing weight, or mood changes, a proper androgen and metabolic panel can either confirm PCOS or point you toward the right diagnosis. Don't settle for a single testosterone reading and a shrug from your GP.

Order the PCOS Clarity 24 test today and get the complete blood picture you need — androgens, metabolic markers, and rule-out tests, all from a single home blood draw.