How PCOS is diagnosed in the UK: criteria, bloods and scans
The Rotterdam criteria explained in plain language, which blood tests are done and why, and what an ultrasound can and cannot show.
is a diagnosis of combination and exclusion. Understanding how that works makes appointments considerably less frustrating.
In short: UK diagnosis follows the Rotterdam criteria - two of three features must be present: irregular or absent ovulation, clinical or biochemical signs of raised androgens, and polycystic-appearing ovaries on ultrasound. disease, high prolactin and adrenal causes must be excluded first.
The three criteria
1. Irregular or absent ovulation. Usually inferred from cycle history: fewer than nine periods a year, or cycles consistently outside the 21-35 day range.
2. Raised androgen activity. Either clinical - acne, hirsutism, scalp hair thinning - or biochemical, on blood testing. Clinical signs count even if bloods are normal.
3. Polycystic-appearing ovaries. Multiple small follicles or increased ovarian volume on ultrasound. This is a supporting feature, not a requirement, and ultrasound is not recommended for diagnosis within eight years of a first period because the appearance is common in that age group.
Two of three, with exclusions done, meets the criteria.
Blood tests you can expect
- Total testosterone and free androgen index
- Sex hormone binding globulin, which is often low where is present
- LH and FSH, sometimes used as supporting information
- Thyroid function, to exclude thyroid disease
- Prolactin, to exclude a prolactin-secreting cause
- 17-hydroxyprogesterone where congenital adrenal hyperplasia is a consideration
- HbA1c or a glucose tolerance test, and a lipid profile, for metabolic
Timing matters: if you are cycling, bloods are often requested in the early follicular phase.
What the scan shows, and does not
A transvaginal ultrasound gives a clearer picture than abdominal scanning. It can show follicle count and ovarian volume. It cannot confirm PCOS on its own, and a normal scan does not exclude it where the other two criteria are met.
After diagnosis
Diagnosis should come with more than a prescription. Reasonable next steps include metabolic screening, a conversation about fertility plans, and a plan for whichever symptom is affecting you most - cycles, skin, hair or fertility.
If you are on hormonal contraception
The pill masks cycle irregularity and reduces androgen symptoms, which makes harder. Do not stop it to get diagnosed without discussing the plan with your clinician first.
Common questions
How long does diagnosis take? Often one appointment for bloods, one for a scan and one for results - typically two to three months in the NHS.
Can PCOS be diagnosed without a scan? Yes, if cycle irregularity and androgen features are both present.
Do I need a specialist? Many women are diagnosed and managed in primary care. Referral is more common for fertility or complex metabolic pictures.
Read the full PCOS guide or find a specialist.