Women's health and hormones
PCOS Blood Test UK: Which Hormones to Check, What Results Mean & How Diagnosis Actually Works
Reviewed by a qualified clinician · analysed at UKAS-accredited UK labs (ISO 15189)
Last reviewed April 202618 min read
Every Helvy guide is written by our health editors, then checked by a qualified clinician before it goes live and re-checked as the science moves. We name clinical roles, not individuals, until each reviewer has agreed to be credited publicly. This is wellness guidance to help you understand your own data, not a diagnosis.
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The core PCOS blood tests look at androgens — total testosterone and the free androgen index — alongside the LH:FSH ratio. Bloods support a diagnosis but do not make one alone. PCOS is identified using the international Rotterdam criteria, which combine clinical signs, blood results and sometimes an ultrasound. A normal testosterone result does not rule it out.
PCOS affects about 1 in 10 UK women. Yet diagnosis takes over two years on average, and many women see three or more clinicians first.
The criteria combine clinical signs, blood tests, and sometimes ultrasound. The NHS often checks one or two markers and stops. A normal testosterone does not rule PCOS out. This guide explains the full panel and where private testing fills a real gap.
1. What is PCOS — and why is it so often missed?
PCOS combines three things: excess androgens (male hormones), irregular or absent ovulation, and, often, polycystic-appearing ovaries. Despite the name, the “cysts” are immature follicles that have stalled, not true cysts.
It looks different in every woman. Some have acne and irregular periods at 16; others find out only when trying to conceive. That is why no single test can diagnose it alone.
The RCOG links PCOS to higher long-term risk of type 2 diabetes (up to 5–10 times), heart disease, and endometrial cancer. Blood testing is the best first step.
2. The Rotterdam criteria: how PCOS is actually diagnosed
The international standard is the Rotterdam criteria, reaffirmed in the 2023 guideline. You need two out of three:
1Oligo-ovulation or anovulation
Irregular periods (cycles over 35 days, fewer than 8 a year) or absent periods for 90+ days.
2Clinical and/or biochemical hyperandrogenism
Clinical: acne, excess hair, or thinning crown hair. Biochemical: raised total or free testosterone, or free androgen index.
3Polycystic ovarian morphology on ultrasound
12 or more follicles per ovary on ultrasound, or ovarian volume over 10 mL. The 2023 guideline raised this to 20 follicles on modern probes.
Other causes must be excluded first: thyroid disease, congenital adrenal hyperplasia, and high prolactin. That is why a full panel matters. It investigates PCOS and rules out mimics at once.
“A diagnosis of PCOS can usually be made if you have at least 2 of the following: irregular or infrequent periods; blood tests showing you have high levels of male hormones; scans showing you have polycystic ovaries.”
— NHS, Polycystic ovary syndrome (Diagnosis)
3. Which hormones does a PCOS blood test check?
A thorough assessment needs more markers than the NHS usually runs:
| Marker | What it tells you | NHS tests it? |
|---|---|---|
| Total testosterone | Primary androgen — elevated in ~60–80% of PCOS cases | Usually |
| Free testosterone / FAI | Biologically active fraction — more sensitive than total testosterone | Sometimes |
| SHBG | Low SHBG amplifies androgen exposure even with normal total T | Rarely |
| LH & FSH | LH:FSH ratio >2:1 is a classic PCOS pattern | Sometimes (often only FSH) |
| Fasting insulin | Insulin resistance drives ~70% of PCOS — fasting glucose alone misses it | Rarely (usually only fasting glucose or HbA1c) |
| DHEA-S | Adrenal androgen — elevated in ~20–30% of PCOS, rules out adrenal source | Rarely |
| AMH | Correlates with follicle count and PCOS severity | No (fertility clinic referral only) |
| TSH & Free T4 | Excludes thyroid dysfunction (symptoms overlap significantly) | Usually |
| Prolactin | Excludes hyperprolactinaemia (causes irregular periods and anovulation) | Sometimes |
| 17-OH progesterone | Screens for non-classical congenital adrenal hyperplasia (mimics PCOS) | Rarely |
The gap is significant. Many women get testosterone and TSH, are told both are normal, and are sent home. SHBG, fasting insulin, DHEA-S, and LH:FSH are never checked.
4. Testosterone & free androgen index: the androgen picture
Testosterone is the key diagnostic androgen, but only 1–3% is active (“free”). The rest binds to SHBG. A woman with normal total T but low SHBG can have excess free androgen and the same symptoms.
The free androgen index (FAI) captures this: (total testosterone ÷ SHBG) × 100. An FAI above 5 meets the hyperandrogenism criterion, even with normal total testosterone.
Why is SHBG so often low? Insulin suppresses it, making a cycle: low SHBG raises free testosterone, which drives more insulin resistance. Breaking it is the point of insulin-sensitising treatment.
When to test:measure testosterone, SHBG, and FAI on days 2–5. Stop hormonal contraception 3 months first, since it raises SHBG and masks androgen excess.
5. LH:FSH ratio: why it matters and when it misleads
Normally, LH and FSH are roughly equal early in the cycle. In classic PCOS the brain favours LH, so the ratio rises, often past 2:1. See our LH and FSH guide.
It appears in about 60% of women with PCOS, per a Human Reproduction study, and is more common in lean PCOS. But it is not a Rotterdam criterion. A normal ratio does not exclude PCOS, so it only adds context.
Timing:measure LH and FSH on days 2–5, drawn together. A mid-cycle sample reads falsely high.
6. Fasting insulin & HOMA-IR: the metabolic root
Insulin resistance affects 50–70% of women with PCOS, lean ones included. Yet the NHS usually screens only with HbA1c or glucose, which stay normal until prediabetes. By then, high insulin has driven symptoms for years.
Fasting insulin is the earliest marker. With glucose it gives the HOMA-IR index; above 2.0 suggests insulin resistance. Research in JCEM found it caught cases with normal glucose and HbA1c that the glucose tests missed. Our insulin resistance guide covers it in full.
Why it matters: if insulin drives your PCOS, insulin-targeting treatment (metformin, inositol, GLP-1 medications) beats anti-androgens alone. Without the test, you are guessing.
7. DHEA-S: the adrenal androgen the NHS rarely tests
DHEA-S comes almost only from the adrenal glands. It does two jobs here.
First, it spots adrenal androgen excess.About 20–30% of women with PCOS have raised DHEA-S, and the pill alone may not resolve it.
Second, it helps exclude congenital adrenal hyperplasia (NCAH),which affects 1–5% of women with PCOS symptoms. A raised DHEA-S with a high 17-OH progesterone needs an ACTH test.
The NHS rarely tests DHEA-S. The NICE guideline CG156 covers testosterone and SHBG but not adrenal androgens.
8. AMH: ovarian reserve and PCOS severity
AMH is made by small ovarian follicles. In PCOS, the extra stalled follicles push it 2–3 times higher. The 2023 guideline, for the first time, allowed AMH instead of ultrasound.
An AMH above 35 pmol/L strongly suggests PCOS, per research in JCEM, and higher levels track more severe disease.
The catch: AMH needs age-specific ranges and is not on the NHS outside fertility clinics.
9. Thyroid & prolactin: ruling out mimics
Both thyroid problems and high prolactin can look just like PCOS.
An underactive thyroid matters most. It raises prolactin, disrupts the cycle, and lowers SHBG. A woman with subclinical hypothyroidism can meet PCOS criteria on bloods, but her thyroid is the treatable cause.
High prolactin can come from a pituitary adenoma, drugs, or stress. Mild rises are usually harmless; levels above 1,000 mIU/L need investigation.
A full workup includes TSH, Free T4, and prolactin. The NHS usually runs only TSH.
10. Reference ranges: what's normal vs what's diagnostic
These ranges are indicative and vary between labs. Always read your results against your own lab report. Draw blood on days 2–5 after an overnight fast.
| Marker | Typical range (female) | PCOS-suggestive |
|---|---|---|
| Total testosterone | 0.5–1.8 nmol/L | >1.8 nmol/L (or upper quartile for lab) |
| Free androgen index (FAI) | <5 | >5 |
| SHBG | 30–90 nmol/L | <30 nmol/L (insulin-driven suppression) |
| LH:FSH ratio (day 2–5) | ~1:1 | >2:1 (supportive, not diagnostic) |
| Fasting insulin | 18–80 pmol/L (<12 µU/mL) | >80 pmol/L (>12 µU/mL) or HOMA-IR >2.0 |
| DHEA-S | 2.7–9.2 µmol/L (age-dependent) | Above upper limit for age |
| AMH | 7–28 pmol/L (age-dependent) | >35 pmol/L (strongly suggestive) |
| TSH | 0.4–4.0 mIU/L | Outside range = investigate thyroid, not PCOS |
One key point: “normal” ranges are population averages. A testosterone of 1.7 nmol/L is technically in range but sits at the top. With low SHBG and symptoms, that is significant. Context beats cut-offs.
11. The NHS PCOS pathway: what gets tested and what gets missed
The NHS approach follows NICE CG156. The typical pathway:
GP appointment for symptom history. Wait: 2–4 weeks.
Bloods ordered: usually testosterone, TSH, sometimes prolactin.
If testosterone is high: referral for ultrasound. Wait: 6–18 weeks.
If testosterone is normal: often no further tests, despite ongoing symptoms.
Step 4 is the problem. A normal testosterone does not rule out PCOS. SHBG may be low, the LH:FSH ratio abnormal, fasting insulin high, or DHEA-S raised. The NHS rarely checks these.
Women trying to conceive reach a fertility clinic for fuller testing. But for those who just want a diagnosis, the NHS pathway often stops early.
12. GP blood test vs Helvy: what's the difference?
| NHS GP | Helvy | |
|---|---|---|
| Androgen markers tested | Testosterone, TSH (sometimes FSH, prolactin) | FSH, LH, SHBG, total testosterone and free androgen index in the Hormone Balance panel |
| SHBG & FAI | Rarely tested — misses androgen excess in normal-T women | Both included in the Hormone Balance panel |
| Fasting insulin | Not routinely available (glucose or HbA1c only) | Not part of any Helvy finger-prick panel — ask your GP or arrange a venous fasting insulin test |
| AMH | Fertility clinic referral only | Not currently offered — fertility clinic referral |
| Wait time | 2–4 weeks for appointment + 1–2 weeks for results | Order today, results usually within 5 working days |
| Sample | Venous draw at phlebotomy clinic | Finger-prick at home |
| Cost | Free | £99 (Hormone Balance panel) |
| Doctor review | Brief letter or phone call | UKAS-accredited report with personalised commentary |
If your GP investigates fully, take it, since it is free and valid. Private testing helps most when the NHS stops at testosterone and TSH, or when you want SHBG and FAI.
13. Common result patterns and what they mean
Pattern 1: Elevated testosterone + high LH:FSH + irregular periods
Classic PCOS. Two Rotterdam criteria are met. Insulin resistance is very likely, so check fasting insulin. Discuss treatment with your GP.
Pattern 2: Normal total testosterone + low SHBG + high FAI + symptoms
“Hidden hyperandrogenism.” Total testosterone is normal, but low SHBG raises free androgen, so FAI meets the criterion. The NHS misses this because it rarely tests SHBG.
Pattern 3: Normal androgens + irregular periods + high fasting insulin
Metabolic PCOS, driven by insulin resistance. Androgens may be normal. It responds best to insulin-sensitising treatment.
Pattern 4: All hormones normal + irregular periods
PCOS is not the only cause of irregular periods. Check thyroid, prolactin, hypothalamic amenorrhoea, and coeliac disease. If all bloods are normal, retest in 3 months.
14. Frequently asked questions
Can a blood test alone diagnose PCOS?
When in my cycle should I have PCOS blood tests?
Does the contraceptive pill affect PCOS blood tests?
Can lean women have PCOS?
What is the best blood test for insulin resistance in PCOS?
How often should I repeat PCOS blood tests?
Get the full picture
Our Hormone Balance panel includes FSH, LH, SHBG, testosterone and free androgen index, the markers at the centre of a PCOS assessment. Fasting insulin and HOMA-IR are not part of any Helvy finger-prick panel, so ask your GP or arrange a venous test. Oestradiol and progesterone are not part of this panel.