Medically reviewed content · Last updated February 2026
A PCOS blood test is one of the most important steps toward a clear diagnosis — yet many women leave their GP appointment with only a basic hormone panel and no real answers. Polycystic ovary syndrome affects roughly 1 in 10 women in the UK, and because its symptoms overlap with thyroid disorders, adrenal conditions, and simple stress, the right combination of blood markers is essential to confirm the diagnosis and rule out mimics.
This guide walks you through every blood test your doctor should consider when investigating PCOS, what each marker reveals, and how to interpret the results.
Key Takeaways
- PCOS is diagnosed using the Rotterdam criteria — you need two of three features: irregular or absent periods, clinical or biochemical hyperandrogenism, and polycystic ovaries on ultrasound (or elevated AMH).
- Core hormone tests include total testosterone, SHBG, free androgen index (FAI), DHEA-S, LH, and FSH.
- Metabolic screening matters — up to 70% of women with PCOS have insulin resistance, so fasting insulin, glucose, HbA1c, and a lipid panel should be part of the workup.
- Exclusion tests (TSH, prolactin, 17-OH progesterone) ensure your symptoms are not caused by thyroid disease, hyperprolactinaemia, or congenital adrenal hyperplasia.
- Timing counts — most hormones should be drawn on cycle days 2–5 for accuracy. If your periods are absent or very irregular, blood can be taken any time.
How Is PCOS Diagnosed?
PCOS remains a clinical diagnosis. There is no single blood test that confirms it on its own. Instead, clinicians use the Rotterdam criteria, the internationally agreed framework since 2003 and reaffirmed in the 2023 international evidence-based guidelines. A diagnosis requires at least two of the following three features:
- Oligo-ovulation or anovulation — irregular, infrequent, or absent menstrual periods (cycles longer than 35 days or fewer than 8 cycles per year).
- Hyperandrogenism — either clinical signs (acne, hirsutism, androgenic hair loss) or elevated androgens on blood tests (biochemical hyperandrogenism).
- Polycystic ovarian morphology — 12 or more follicles (2–9 mm) per ovary on ultrasound, or an ovarian volume greater than 10 mL. Under the 2023 update, an elevated AMH level can now be used in place of ultrasound in adults.
Crucially, other conditions that mimic PCOS must be excluded first — thyroid dysfunction, congenital adrenal hyperplasia, Cushing’s syndrome, hyperprolactinaemia, and androgen-secreting tumours. This is where blood tests become essential.
Essential PCOS Blood Tests
The following hormone markers form the core of a PCOS blood test panel. Together they assess androgen levels and the pituitary hormones that regulate ovulation.
| Blood Test | What It Shows | Expected in PCOS | Typical Normal Range |
|---|---|---|---|
| Total Testosterone | Primary androgen; the most sensitive biochemical marker for PCOS | Elevated (often 1.5–3× upper limit) | 0.3–1.7 nmol/L |
| SHBG | Protein that binds testosterone; low SHBG means more free (active) testosterone | Low | 30–90 nmol/L |
| Free Androgen Index (FAI) | Calculated ratio (testosterone ÷ SHBG × 100); reflects biologically active testosterone | Elevated (>5) | <5 |
| DHEA-S | Adrenal androgen; helps distinguish ovarian from adrenal androgen excess | Normal or mildly elevated | 1.0–11.7 µmol/L |
| LH (Luteinising Hormone) | Pituitary hormone that triggers ovulation; drives ovarian androgen production | Elevated (often >10 IU/L in follicular phase) | 2–13 IU/L (follicular) |
| FSH (Follicle-Stimulating Hormone) | Pituitary hormone that stimulates follicle growth; usually normal in PCOS | Normal or low-normal | 3.5–12.5 IU/L (follicular) |
| LH:FSH Ratio | High ratio suggests disrupted ovulation typical of PCOS | >2:1 (often >3:1) | ~1:1 |
| AMH (Anti-Müllerian Hormone) | Reflects ovarian follicle count; can now replace ultrasound under 2023 guidelines | Elevated (often 2–4× normal) | 1.0–3.5 ng/mL (age-dependent) |
A raised free androgen index is widely considered the single most useful biochemical marker for PCOS because it captures both high testosterone and low SHBG in one number. If your GP has only tested total testosterone, you may have been told your androgens are “normal” when your FAI would actually flag an abnormality.
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PCOS is not only a reproductive condition. Up to 70% of women with PCOS have some degree of insulin resistance, regardless of body weight. Insulin resistance drives androgen overproduction, worsens symptoms, and significantly increases the long-term risk of type 2 diabetes and cardiovascular disease. That is why metabolic blood tests should be part of every PCOS investigation.
| Blood Test | Why It’s Needed | What to Look For |
|---|---|---|
| Fasting Insulin | Detects insulin resistance before glucose levels rise | >10 mU/L suggests resistance; >20 mU/L strongly indicative |
| Fasting Glucose | Screens for impaired fasting glucose and diabetes | Normal <5.5 mmol/L; 5.5–6.9 = pre-diabetes; ≥7.0 = diabetes |
| HOMA-IR | Calculated from fasting insulin and glucose; the most validated insulin resistance index in PCOS | >2.0 suggests insulin resistance |
| HbA1c | Average blood sugar over 2–3 months; screens for diabetes | <42 mmol/mol (5.7%) normal; 42–47 = pre-diabetes; ≥48 = diabetes |
| Lipid Panel (total cholesterol, LDL, HDL, triglycerides) | PCOS raises cardiovascular risk; dyslipidaemia is common | High triglycerides and low HDL are the classic PCOS pattern |
A note on HOMA-IR: Many GPs do not routinely test fasting insulin — only fasting glucose. The problem is that glucose may remain normal for years while insulin levels climb. If your glucose comes back “fine” but you have PCOS symptoms, ask specifically for a fasting insulin level or an oral glucose tolerance test (OGTT) with insulin measurements.
Tests to Rule Out Other Conditions
Because PCOS is a diagnosis of exclusion, your GP should check for conditions that produce similar symptoms before confirming it. The three essential exclusion tests are:
1. Thyroid Function (TSH and Free T4)
Both an underactive thyroid (hypothyroidism) and an overactive thyroid can cause irregular periods, weight changes, fatigue, and hair thinning — symptoms easily mistaken for PCOS. A simple TSH test (normal range roughly 0.4–4.0 mIU/L) is the first-line screen. If TSH is abnormal, free T4 and free T3 follow.
2. Prolactin
Prolactin is a pituitary hormone. Elevated levels (hyperprolactinaemia) can suppress ovulation and raise androgens, mimicking PCOS closely. Common causes include pituitary adenomas and certain medications. A fasting morning blood draw is best — stress, exercise, and eating can temporarily raise prolactin. Normal range for women is typically <25 µg/L.
3. 17-OH Progesterone (17-OHP)
This test screens for non-classical congenital adrenal hyperplasia (NCAH), an inherited enzyme deficiency that causes the adrenal glands to overproduce androgens. NCAH affects roughly 1–5% of women initially suspected of having PCOS, so it is not rare. An early morning, follicular-phase 17-OHP below 6 nmol/L (or 200 ng/dL) generally excludes NCAH. If borderline, a synacthen (ACTH stimulation) test may follow.
Other Tests Your Doctor May Consider
- 24-hour urinary cortisol or overnight dexamethasone suppression test — to rule out Cushing’s syndrome if features such as central obesity, proximal muscle weakness, or purple striae are present.
- Androstenedione — another androgen that may be elevated in PCOS; can help characterise the androgen profile further.
- Vitamin D — deficiency is prevalent in PCOS and may worsen insulin resistance and mood symptoms.
When to Test: Cycle Day Timing Matters
Hormone levels fluctuate dramatically across the menstrual cycle, so testing at the wrong time can produce misleading results. Here is the recommended timing for each category of test:
- LH, FSH, oestradiol, testosterone, SHBG, FAI: Draw blood on cycle days 2–5 (day 1 = first day of your period). This is the early follicular phase, when these hormones are at their most stable baseline. If your GP draws LH later in the cycle, it may coincide with the natural LH surge and appear falsely elevated.
- Progesterone: If ovulation confirmation is needed, progesterone is tested on day 21 of a 28-day cycle (or 7 days before your expected period). A level >30 nmol/L confirms ovulation.
- Fasting insulin, glucose, HbA1c, lipids: Can be drawn any day of the cycle, but must be fasting (8–12 hours overnight, water only).
- Prolactin: Best drawn fasting, morning, at rest. Avoid exercise beforehand.
- AMH, DHEA-S, 17-OHP, TSH: Relatively cycle-independent — can be tested on any day.
- If your periods are absent or very irregular (cycles >6 weeks): blood can be taken on any day, as there is no reliable follicular phase to target.
Tip: When booking your appointment, tell the receptionist you need an early-morning fasting blood draw on day 2–5 of your cycle so that all tests can be done in a single visit.
Understanding Your Results
Receiving a stack of blood results can feel overwhelming. Here is how to interpret the key patterns:
- High FAI or high total testosterone + low SHBG — this is the hallmark biochemical finding in PCOS. It confirms hyperandrogenism even when total testosterone alone is in the “normal” range.
- LH:FSH ratio >2:1 — suggestive of PCOS but no longer required for diagnosis. About 60% of women with PCOS show a raised ratio.
- AMH >3.5–5.0 ng/mL — elevated AMH is now an accepted alternative to ovarian ultrasound for confirming polycystic morphology. Bear in mind that AMH declines naturally with age, so age-specific reference ranges should be used.
- Fasting insulin >10 mU/L or HOMA-IR >2.0 — points to insulin resistance. This does not diagnose PCOS itself, but it guides treatment decisions (for instance, metformin or inositol supplementation may be recommended).
- Normal TSH, prolactin, and 17-OHP — these rule out the main mimicking conditions and strengthen the PCOS diagnosis.
Remember that no single result confirms or excludes PCOS. Your doctor should interpret the full panel alongside your symptoms, menstrual history, and clinical examination. If you feel your concerns have been dismissed after only a partial set of tests, you are within your rights to request the additional markers outlined above or seek a second opinion.
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If you suspect PCOS, start by tracking your menstrual cycle length for two to three months and noting any symptoms such as acne, excess hair growth, or thinning hair. Book a fasting morning blood draw on day 2–5 of your cycle and bring a written list of the tests above — particularly FAI, fasting insulin, and 17-OHP, which are frequently omitted from standard panels. If your GP is reluctant to run the full set, a home blood test can fill the gaps and give you data to discuss at your next appointment. Early diagnosis means earlier access to treatment, better symptom management, and significantly lower long-term metabolic risk.
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Frequently Asked Questions
What blood test is done for PCOS?
A PCOS blood test panel typically includes total testosterone, SHBG, free androgen index, LH, FSH, DHEA-S, and AMH to assess hormone levels. Metabolic tests such as fasting insulin, fasting glucose, HbA1c, and a lipid panel check for insulin resistance and cardiovascular risk. Thyroid function (TSH), prolactin, and 17-OH progesterone are added to rule out conditions that mimic PCOS.
Can a blood test confirm PCOS?
No single blood test confirms PCOS on its own. Diagnosis follows the Rotterdam criteria and requires at least two of three features: irregular ovulation, hyperandrogenism (clinical or biochemical), and polycystic ovaries on ultrasound or an elevated AMH. Blood tests provide the biochemical evidence and help exclude other conditions.
What day of my cycle should I have my PCOS blood test?
Hormone tests such as LH, FSH, testosterone, and SHBG should be drawn on cycle days 2 to 5 (the early follicular phase) for the most accurate results. If your periods are absent or very irregular (cycles longer than six weeks), you can have the blood draw on any day. Fasting metabolic markers, AMH, and thyroid tests are not cycle-dependent.
What is the LH:FSH ratio in PCOS?
In PCOS the LH:FSH ratio is often greater than 2:1 and sometimes above 3:1, compared with a roughly 1:1 ratio in women without the condition. However, a raised ratio is seen in only around 60% of PCOS cases, so a normal ratio does not exclude the diagnosis. Current guidelines no longer require a raised LH:FSH ratio for diagnosis.
Why is insulin tested in PCOS?
Up to 70% of women with PCOS have insulin resistance, which means their cells respond poorly to insulin and the pancreas produces more to compensate. Excess insulin stimulates the ovaries to produce more testosterone, worsening symptoms. Fasting insulin and HOMA-IR detect insulin resistance early — often years before fasting glucose or HbA1c become abnormal.
What is a free androgen index and why does it matter?
The free androgen index (FAI) is calculated as total testosterone divided by SHBG, multiplied by 100. It estimates how much biologically active testosterone is circulating. In PCOS, SHBG is often low, which pushes FAI above 5 even when total testosterone looks normal. That makes FAI a more sensitive marker for hyperandrogenism than total testosterone alone.
Should I test for PCOS at home?
Home finger-prick blood test kits can measure the key hormones and metabolic markers relevant to PCOS. They are a practical option if you want to gather data before a GP appointment, monitor treatment progress, or investigate symptoms when NHS waiting times are long. Make sure the kit covers testosterone, SHBG, FAI, LH, FSH, and ideally fasting insulin and thyroid function. Results should always be reviewed with a healthcare professional for a formal diagnosis.
Can I have PCOS with normal testosterone?
Yes. Total testosterone is normal in roughly 20–30% of women with PCOS. The diagnosis can be made on other criteria — for instance, irregular periods combined with polycystic ovaries on ultrasound. Additionally, SHBG may be low, giving a high free androgen index despite a normal total testosterone reading. This is why testing SHBG and calculating FAI is so important.
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