PCOS is diagnosed using the Rotterdam criteria, agreed in 2003 and still the international standard. A diagnosis requires two of three features, with other conditions excluded.
Irregular or absent ovulation, usually showing as cycles longer than 35 days, fewer than eight periods a year, or none at all.
Excess androgens, either measured on a blood test or visible as acne, unwanted facial or body hair, or hair thinning at the crown.
Polycystic ovaries on ultrasound, meaning many small follicles or enlarged ovaries.
Because only two are needed, you can have PCOS with completely normal-looking ovaries. That surprises many women, and it is why the name is misleading: those follicles are not cysts, and they are not the defining feature.
It scores your symptoms against those criteria and tells you whether the pattern is consistent with PCOS. It cannot diagnose, because two of the three features require a blood test and a scan.
What it can do is tell you whether the conversation is worth having, and what to ask for.
Insulin resistance affects a large majority of women with PCOS, including many who are not overweight. It drives the whole picture: high insulin prompts the ovaries to produce more testosterone, which disrupts ovulation and causes the skin and hair symptoms.
This matters because treating the insulin side often improves everything downstream, and because it carries longer-term risk. Women with PCOS have substantially higher rates of type 2 diabetes.
Yet many women are diagnosed and offered the pill without anyone checking fasting insulin or HbA1c.
If your result suggests PCOS is worth investigating:
Blood tests — total testosterone, SHBG and free androgen index, LH and FSH, plus prolactin and thyroid function to exclude the conditions that mimic it.
Metabolic markers — fasting glucose, fasting insulin and HbA1c. These are the ones most often skipped, and the HOMA-IR calculator here works out insulin resistance from two of them.
A pelvic ultrasound, though remember this is only one of three criteria and a normal scan does not exclude PCOS.
Timing matters for hormone tests. If you still have periods, days two to five of your cycle is standard.
Treatment depends on what troubles you most: irregular cycles, skin and hair symptoms, fertility, or metabolic health.
Across all of them, improving insulin sensitivity is the intervention that touches everything. Resistance training, adequate protein, and modest weight loss where relevant all work through that mechanism. Metformin and, increasingly, GLP-1 medications are used for the same reason.
The pill regulates cycles and improves skin symptoms but does not address the underlying insulin picture, which is worth knowing when it is offered as the whole answer.
Related reading: PCOS explained · GLP-1 medications and your hormones · Insulin resistance calculator · Adult hormonal acne
Educational only, not medical advice. PCOS is diagnosed by a doctor using blood tests and imaging.