How Is PCOS Diagnosed? Tests and Criteria

How is PCOS diagnosed is a question many people ask after months or even years of unexplained symptoms. Polycystic ovary syndrome affects roughly 1 in 10 people with ovaries in the UK, yet it frequently goes unrecognised because its features overlap with other conditions and no single test can confirm it alone. Diagnosis relies on a structured clinical assessment using the Rotterdam criteria, combining menstrual history, hormone blood tests and, where needed, a pelvic ultrasound scan. This article explains the full diagnostic process, which symptoms to discuss with your GP, and what to expect after a diagnosis.

What is PCOS and why is it sometimes hard to identify?

PCOS is a hormonal syndrome requiring any two of three diagnostic features, making it difficult to identify because symptoms overlap with other conditions and no single test confirms it alone.

Polycystic ovary syndrome (PCOS) is a common hormonal condition affecting women and people with ovaries, characterised by a combination of irregular periods, elevated androgen levels and polycystic-appearing ovaries on ultrasound. NHS and NICE sources estimate it affects roughly 1 in 10 people with ovaries in the UK, though many remain undiagnosed for years.^[6][5] PCOS is not a single disease with one clear cause; it is a syndrome, meaning it is defined by a cluster of features rather than a single diagnostic marker.

Importantly, a person does not need to have all three features for a diagnosis to be made. Diagnosis requires any two of the three recognised features, after other conditions have been excluded. This means someone with irregular periods and signs of androgen excess may receive a diagnosis even without polycystic-appearing ovaries on scan, and vice versa.

One reason PCOS can be difficult to identify is that its symptoms overlap considerably with other conditions. Irregular periods may be attributed to stress or thyroid disorders, excess hair growth may be dismissed as a cosmetic concern, and weight changes are often attributed to lifestyle factors alone. Because no single blood test or scan can confirm PCOS in isolation, diagnosis requires a careful assessment of multiple findings.

The condition also presents very differently between individuals. Some people experience significant menstrual disruption and fertility difficulties, while others have subtle hormonal changes with few outward signs. This variability means that two people with PCOS may describe quite different experiences, which can delay recognition both by patients and clinicians. Raising awareness of the full range of presentations is an important step towards earlier diagnosis and appropriate support.

How do doctors in the UK diagnose PCOS?

UK doctors diagnose PCOS using the Rotterdam criteria, requiring at least two of three features, after excluding other causes such as thyroid dysfunction, hyperprolactinaemia and congenital adrenal hyperplasia.

In the UK, PCOS is diagnosed using the Rotterdam criteria, which require at least two of the following three features to be present: irregular or absent ovulation (typically reflected in irregular or infrequent periods), clinical or biochemical signs of elevated androgens, and polycystic-appearing ovaries on ultrasound.^[1][2] NICE Clinical Knowledge Summary (CKS) guidance on PCOS supports this approach, and a diagnosis is only made after other conditions that could explain the symptoms have been excluded.^[1][2]

A GP will usually begin with a detailed clinical history, asking about menstrual cycle regularity, symptoms such as acne, excess facial or body hair (hirsutism), scalp hair thinning, and any difficulties with weight management. They will also ask about fertility concerns and family history, as PCOS can run in families. A physical examination may be carried out to assess signs of androgen excess.

For anyone presenting with delayed, infrequent or absent periods, a pregnancy test is an important first-line step before further investigation. Beyond this, the diagnostic process involves ruling out other causes, including thyroid dysfunction, hyperprolactinaemia, non-classical congenital adrenal hyperplasia (CAH), primary ovarian insufficiency, Cushing's syndrome, androgen-secreting tumours and pregnancy. This means it can take more than one appointment to reach a diagnosis.

Clear referral triggers to endocrinology or gynaecology include: signs of virilisation (such as voice deepening or clitoromegaly), very high or rapidly rising androgen levels, diagnostic uncertainty after initial assessment, or fertility concerns requiring ovulation induction. This stepwise approach, while sometimes frustrating for patients, is important for ensuring the correct diagnosis and the most appropriate management plan. If you are seeking support alongside NHS care, Bolt Pharmacy is a GPhC-registered UK online pharmacy offering online consultations with prescriber review and pharmacist support for a range of hormonal and metabolic health concerns.

Which tests and scans are used to confirm PCOS?

Diagnosis typically involves blood tests for testosterone, SHBG, LH, FSH, thyroid function, prolactin and glucose regulation, plus a pelvic ultrasound if two Rotterdam criteria are not already met clinically.

Several blood tests and an ultrasound scan are typically used as part of the diagnostic workup for PCOS. Blood tests commonly requested include:

• Total and free testosterone: to identify biochemical androgen excess

• Sex hormone-binding globulin (SHBG): low levels can indicate androgen excess even when total testosterone appears normal

• LH (luteinising hormone) and FSH (follicle-stimulating hormone): measured not as diagnostic tests for PCOS itself, but to help exclude other causes such as primary ovarian insufficiency; the LH/FSH ratio alone is not considered diagnostic for PCOS in UK guidance^[2][5]

• Thyroid function tests (TFTs): to exclude thyroid disorders as a cause of irregular periods

• Prolactin: to rule out hyperprolactinaemia

• Morning 17-hydroxyprogesterone: to exclude non-classical congenital adrenal hyperplasia, particularly in those with significant androgen excess^[2][5]

• Fasting lipid profile: as part of metabolic risk assessment, given the association between PCOS and cardiovascular risk factors

• Glycaemic assessment: a 75 g oral glucose tolerance test (OGTT) is the preferred method for assessing glucose regulation at baseline; HbA1c may be used as an alternative where an OGTT is not feasible.^[2][3] Measuring fasting insulin alone is not routinely recommended in UK primary care, as it does not aid diagnosis and assay results vary^[2][5]

A pelvic ultrasound scan is used to assess ovarian morphology. The current threshold for polycystic ovarian morphology (PCOM) in adults, as updated in international guidance, is the presence of 20 or more follicles per ovary or an ovarian volume greater than 10 ml in either ovary. This threshold applies when using modern high-frequency transvaginal probes (8 MHz or above); follicle counts from transabdominal scans are less reliable, and ovarian volume criteria may be more appropriate in that setting. It is also important to note that if two of the three Rotterdam criteria are already met on clinical and biochemical grounds, an ultrasound scan is not required to make the diagnosis.

Polycystic-appearing ovaries alone do not confirm PCOS; the finding must be interpreted alongside clinical and biochemical results.

In adolescents, ultrasound is generally not recommended as a diagnostic tool within eight years of the first period, as polycystic ovarian morphology can be a normal variant during this time. In younger patients, diagnosis should rely on persistent oligo-ovulation or anovulation combined with clinical or biochemical hyperandrogenism, after other causes have been excluded.

What symptoms should prompt you to see your GP?

See your GP if you have persistent irregular or absent periods, excess facial or body hair, acne, scalp hair thinning, unexplained weight gain, or difficulty conceiving, as even one or two of these warrants assessment.

You should see your GP if you experience persistent irregular, infrequent or absent periods. As a practical guide, no period for three months warrants assessment. Other symptoms that warrant a GP appointment include:

• Excess hair growth on the face, chest, back or abdomen (hirsutism)

• Acne that is persistent, severe or not responding to standard treatments

• Thinning hair or hair loss from the scalp (alopecia)

• Unexplained weight gain, particularly around the abdomen

• Difficulty conceiving after regular unprotected intercourse

• Skin changes such as darkening of the skin in skin folds (acanthosis nigricans), which can indicate insulin resistance

If you have missed periods or your period is significantly delayed, do a pregnancy test before your appointment, as pregnancy is an important first exclusion.

You do not need to have all of these symptoms to seek advice. Even one or two of the above, particularly irregular periods combined with signs of androgen excess, is sufficient reason to discuss your concerns with a GP. Early assessment is valuable because PCOS is associated with longer-term metabolic health considerations, including an increased risk of type 2 diabetes and cardiovascular risk factors, which benefit from early identification and lifestyle support.

Seek same-day medical attention or contact NHS 111 if you experience heavy or prolonged bleeding causing dizziness or faintness, severe acute pelvic pain, or rapidly progressive symptoms such as significant voice changes or other signs of virilisation, as these require prompt assessment to exclude other causes.

If your symptoms are causing significant distress, affecting your fertility plans or your mental wellbeing, do not wait for them to worsen before seeking help. Your GP can initiate the appropriate investigations and refer you to a specialist if needed. There is no need to have a definitive self-diagnosis before making an appointment.

What happens after a PCOS diagnosis on the NHS?

Post-diagnosis NHS management is individualised and may include lifestyle interventions, the combined oral contraceptive pill for cycle regulation, letrozole for ovulation induction, or metformin where insulin resistance is present.

After a PCOS diagnosis, management on the NHS is tailored to the individual's symptoms, priorities and reproductive goals, as there is no single treatment that addresses all aspects of the condition. NICE guidance recommends that lifestyle interventions, particularly a balanced diet and regular physical activity, are offered as a first-line approach for people with PCOS who are overweight, given the significant impact of even modest weight loss on hormonal balance, menstrual regularity and metabolic health.

For those whose primary concern is menstrual irregularity, a combined oral contraceptive pill is commonly prescribed to regulate cycles and reduce androgen-related symptoms such as acne and hirsutism. For people with infrequent periods who are not using combined hormonal contraception, endometrial protection is important: cyclical progestogens or a levonorgestrel intrauterine system may be recommended to reduce the risk of endometrial changes associated with prolonged anovulation.^[2][5]

For people trying to conceive, letrozole is recommended as first-line treatment for ovulation induction in anovulatory PCOS, in line with NICE fertility guidance.^[11][5] Referral to a specialist fertility service can be arranged through the NHS where needed. Metformin, a medicine that improves insulin sensitivity, may be offered in certain cases, particularly where there is evidence of insulin resistance or impaired glucose regulation.

Ongoing monitoring is an important part of PCOS care. People with PCOS are typically advised to have periodic checks of blood pressure, BMI and waist circumference, fasting lipids, and glycaemic status (using an OGTT or HbA1c), with the frequency of monitoring guided by individual metabolic risk. Mental health support should also be considered, as PCOS is associated with higher rates of anxiety and depression.^[12][13]

Your GP may refer you to an endocrinologist, gynaecologist or a specialist PCOS clinic depending on your needs. If you have concerns between appointments, NHS 111 can provide advice, or you can contact your GP practice directly. Staying engaged with follow-up care is important for managing PCOS effectively over the long term.

Scientific References

1. Polycystic ovary syndrome: assessment and management (GID-NG10436) – supporting documentation 9.
2. Polycystic ovary syndrome (GID-NG10436) – supporting documentation 8.
3. Polycystic ovary syndrome (GID-NG10436) – document 450.
4. Polycystic ovary syndrome: Adaptation report 3 (GID-NG10436).
5. Polycystic ovary syndrome | Treatment summaries – BNF – NICE.
6. Rising Incidence, Health Resource Utilization, and Costs of Polycystic Ovary Syndrome.
7. Ultrasonographic criteria in the diagnosis of polycystic ovary syndrome: a systematic review and diagnostic meta-analysis. Human Reproduction Update..
8. Updated ultrasound criteria for polycystic ovary syndrome: reliable thresholds for elevated follicle population and ovarian volume. Human Reproduction..
9. Definition and significance of polycystic ovarian morphology: a task force report from the Androgen Excess and Polycystic Ovary Syndrome Society. Human Reproduction Update..
10. Adolescent polycystic ovary syndrome according to the international evidence-based guideline. BMC Medicine..
11. Letrozole as first-line drug for ovulation induction in polycystic ovary syndrome..
12. Depressive and Anxiety Symptoms in Women with Polycystic Ovary Syndrome: A Meta-Analysis. Journal of Clinical Medicine..
13. Prevalence and outcomes of co-occurring psychiatric and endocrine, metabolic, and nutritional disorders. European Neuropsychopharmacology..

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