PCOS Diagnosis: What Gets Tested, and In What Order

The diagnosis is a subtraction, not a single test

There is no blood test that says yes or no. A clinician counts how many of three features you have, and separately rules out the other conditions that produce the same picture. Both halves have to happen. A diagnosis made on one feature, or made without the exclusion bloods, is not a diagnosis that has been done properly.

The framework comes from the 2003 Rotterdam consensus and was refined — not replaced — by the 2023 International Evidence-based Guideline, which is what most clinicians work from today. If you want the criteria set out line by line rather than as a process, that is the criteria page.

One thing has changed since, and it is only the word. In May 2026 a global consensus process published in The Lancet renamed the condition polyendocrine metabolic ovarian syndrome, or PMOS. The biology, the tests and the thresholds are untouched. A 2026 letter saying PMOS and a 2024 letter saying PCOS record the same result. The background to the change is here.

Feature 1 — your cycle, counted in days

This costs nothing and it is the piece most often decided before you get to the clinic. The guideline defines “irregular” by how long it has been since your first period, because young cycles are legitimately erratic.

Years since first period	Counts as irregular
Under 1 year	Nothing — irregularity here is normal pubertal transition
1 to 3 years	Cycles shorter than 21 days or longer than 45 days
More than 3 years	Cycles shorter than 21 days or longer than 35 days, or fewer than 8 cycles a year
More than 1 year	Any single cycle longer than 90 days
Any	No period by age 15, or more than 3 years after breasts began developing

Cycles can look regular and still not be ovulatory. Where the cycle length is normal but ovulation is in doubt, a progesterone level drawn about a week before the expected period is what settles it.

Before the appointment: write down the start date of your last six periods. Three months of dates does more for the conversation than any symptom you can describe.

Feature 2 — androgens, measured two ways

Excess androgen counts if it shows up clinically or biochemically. You do not need both.

Clinically means hirsutism — coarse, dark hair in a male pattern — scored on the modified Ferriman–Gallwey scale, where a score of roughly 4 to 6 and above indicates hirsutism, with the cut-off varying by ethnicity. Female pattern hair loss and persistent acne are also counted, although both are less specific on their own.

Biochemically means a blood test. The guideline directs clinicians to calculated free testosterone, the free androgen index, or calculated bioavailable testosterone, using high-quality assays such as liquid chromatography–mass spectrometry. Direct immunoassays for free testosterone are specifically advised against, because they are not accurate enough at female concentrations.

Feature 3 — the scan, or the AMH test instead of it

This is the feature most people expect first and the one most often unnecessary.

On a transvaginal ultrasound, polycystic ovarian morphology means 20 or more follicles in either ovary, or an ovarian volume of 10 mL or more, in the absence of a dominant follicle or corpus luteum. Those specks are immature follicles. They are not cysts, and the name change exists partly because that word misled people for fifty years.

The 2023 guideline’s single biggest update was allowing AMH as an alternative to ultrasound in adults. A 2024 systematic review and meta-analysis of 82 studies — the analysis the guideline commissioned — found a pooled sensitivity of 0.79 and specificity of 0.87 for AMH in adults. In adolescents the numbers fell to 0.66 and 0.78, which is why AMH is not used under that age. The same review could not recommend an international cut-off value, because assays and reference ranges differ between labs.

When you do not need a scan at all

If you have irregular cycles and hyperandrogenism, you already have two of three. The guideline states that neither ultrasound nor AMH is necessary in that situation. If a clinic is sending you for a transvaginal scan you did not want when both boxes are already ticked, that is a reasonable thing to ask about.

What has to be ruled out first

These are the conditions that mimic the same picture. Skipping them is the most common way a diagnosis goes wrong.

Test	Rules out	Why it looks the same
TSH	Thyroid disease	Both under- and overactive thyroid disrupt cycles
Prolactin	Hyperprolactinaemia	Raised prolactin stops ovulation and periods
17-hydroxyprogesterone (early morning, follicular phase)	Non-classical congenital adrenal hyperplasia	Produces hirsutism and irregular cycles from an adrenal cause
Further testing, if features fit	Cushing’s syndrome, androgen-secreting tumour, acromegaly	Considered when androgen excess is severe, rapid in onset, or accompanied by virilisation

Rapid onset matters here. Hirsutism that arrived over months rather than years, or a deepening voice, prompts a different and more urgent workup. Say so explicitly if it applies to you.

Four ways to meet the criteria — and why yours matters

Two of three can be satisfied in four combinations, which is why two people with the same diagnosis can look nothing alike.

Phenotype	Androgen excess	Irregular cycles	Polycystic ovaries / high AMH
A	Yes	Yes	Yes
B	Yes	Yes	No
C (ovulatory)	Yes	No	Yes
D (non-hyperandrogenic)	No	Yes	Yes

The practical consequence: androgen-positive phenotypes A and B tend to carry the heavier metabolic picture, so the follow-up testing your clinician orders after the diagnosis should not be identical for everyone. If you do not yet know which pattern fits you, start with the four types.

This also explains a number people find confusing. A 2016 systematic review and meta-analysis put PCOS prevalence at 6% under the narrower NIH criteria and 10% under Rotterdam — the same condition, different counting rules. That review also found polycystic ovaries on ultrasound in 28% of women across these populations. Far more people have the scan finding than have the syndrome, which is exactly why the scan alone never was the diagnosis.

If you are under 20

Adolescents are held to a stricter standard, deliberately, to avoid labelling normal puberty. Diagnosis needs irregular cycles and hyperandrogenism — the first two features only. Pelvic ultrasound is not recommended within 8 years of menarche, and AMH is not used at all in this age group.

Where features are present but the criteria are not met, the guideline supports an “at risk” label, with symptoms treated and a review later. That is a real clinical position, not a brush-off.

Why it so often takes years — and the one thing that shortens it

In a cross-sectional online survey of 1,385 women recruited through support-group websites, 33.6% reported more than two years and 47.1% reported seeing three or more health professionals before a diagnosis was established. Only 15.6% were satisfied with the information they received. It is self-selected and observational, so read it as a description of a common experience rather than a population rate — but it matches what almost everyone reports.

The pattern in that data is a fragmented history: the acne mentioned to one clinician, the periods to another, the weight to a third. Nobody sees the two-of-three shape because nobody has all three pieces in front of them.

So bring all three yourself, on one page.

Your next step, this week

Write down four things and take them to one appointment:

1. Start dates of your last six periods — or “none since [month]”.
2. Androgen signs, with when they started — hair, acne, scalp thinning, and whether the change was gradual or fast.
3. Any hormonal contraception, and how long you have been on it.
4. One sentence: “I’d like to be assessed for PCOS — can we check TSH, prolactin, 17-hydroxyprogesterone and androgens, and go from there?”

That request names the exclusion bloods, which is the step most often skipped. If you want help phrasing the rest of that conversation, there is a script for it here, and the wider diagnosis section covers what happens after the letter arrives.