How PCOS Is Actually Diagnosed, and Why AMH Was Added in 2023

The short answer

Polycystic ovary syndrome is diagnosed by counting features, not by a single test. Under the Rotterdam framework carried forward by the 2023 International Evidence-based Guideline, an adult meets criteria when two of three findings are present: irregular menstrual cycles, clinical or biochemical hyperandrogenism, and polycystic ovarian morphology. The 2023 update's most talked-about change was adding serum anti-Mullerian hormone (AMH) as an alternative to pelvic ultrasound for that third feature. The same guideline also drew a firm age line to keep the diagnosis from being applied too loosely in teenagers. This article is educational and not medical advice.

Two of three, and why that structure matters

PCOS is a syndrome, which means it is defined by a pattern rather than by one abnormal number. The 2023 guideline, published in the Journal of Clinical Endocrinology and Metabolism, keeps the Rotterdam structure: any two of the three features establish the diagnosis in an adult, once other conditions are ruled out.

That "two of three" design has a practical consequence many people miss. If someone already has irregular cycles and clear signs of excess androgen, they have met two criteria and the diagnosis is complete without imaging or bloodwork for the ovaries. The guideline says this directly. Practice Point 1.4.9 states that in patients with irregular menstrual cycles and hyperandrogenism, an ovarian ultrasound is not necessary for PCOS diagnosis. Recommendation 1.5.2 extends the same logic to the new blood test: in that situation, an AMH level is not necessary either.

The third feature, polycystic ovarian morphology, only becomes decisive when one of the other two is missing or uncertain. It is the tiebreaker, not the centerpiece. Understanding that ordering prevents a common error, which is treating a "polycystic-appearing" ovary on a scan as if it alone means disease. It does not.

What "polycystic ovarian morphology" actually means

The term is misleading in everyday language. The follicles counted on ultrasound are not cysts in the way most people picture them. Morphology is defined by follicle number: the guideline's threshold is 20 or more follicles measuring 2 to 9 millimeters in at least one ovary on a good-quality transvaginal scan. A high count is common in the general population, especially in younger women, which is exactly why it cannot stand alone.

Why AMH was added

Anti-Mullerian hormone is made by the granulosa cells of small growing follicles in the ovary. Because more of those follicles means more hormone, blood AMH strongly correlates with the antral follicle count that a sonographer would tally on a screen. In PCOS, AMH levels typically run about two to threefold higher than in unaffected women. That biological link is what let the guideline treat AMH as a stand-in for the ultrasound measure of morphology.

The motivation was access, not novelty. A transvaginal ultrasound requires equipment, a trained operator, and a setting many primary care and general practices do not have. A blood draw does not. Recommendation 1.5.1 states that serum AMH could be used for defining polycystic ovarian morphology in adults, which opens the diagnostic pathway to clinicians who cannot easily order imaging.

The guideline is careful to prevent the two tests from stacking. Practice Point 1.5.5 says either serum AMH or ultrasound may be used to define morphology, but both should not be performed, specifically to limit overdiagnosis. Running two overlapping tests only raises the chance that a normal person trips a threshold by chance.

The important limits on AMH

AMH is a useful surrogate, not a shortcut around the whole framework. The evidence review behind the guideline is blunt that using AMH as a single marker for PCOS has poor sensitivity and specificity, and that AMH as a sole marker is not recommended. A high AMH by itself diagnoses nothing. It substitutes only for the morphology criterion, which still has to be combined with irregular cycles or hyperandrogenism.

There is also a laboratory problem. AMH assays are not standardized across manufacturers, so the same sample can yield meaningfully different numbers depending on the platform. Published diagnostic cutoffs have ranged widely, roughly 3 to 10 nanograms per milliliter across studies, precisely because the assays disagree. For that reason the guideline directs laboratories to use population and assay-specific cutoffs rather than one universal line. A result means little without knowing which assay produced it and what threshold that assay uses.

The age rule that guards against overdiagnosis

The most protective part of the 2023 update is a boundary, not a test. Both ultrasound and AMH lose specificity in the years right after a first period, because high follicle counts and high AMH are normal parts of a maturing reproductive system. Reading them as disease in that window would label healthy adolescents.

So the guideline restricts both. Neither ovarian morphology by ultrasound nor AMH should be used to diagnose PCOS within eight years of menarche. Recommendation 1.4.6 states ultrasound is not recommended in adolescents, and Recommendation 1.5.4 states serum AMH should not yet be used in adolescents. For a teenager, then, the diagnosis rests on the other two features together: irregular cycles and hyperandrogenism, both required.

The guideline also creates a holding category instead of forcing an answer. Under Practice Point 1.1.4, an adolescent who has features of PCOS but does not fully meet criteria can be considered at increased risk, with reassessment advised at or before full reproductive maturity, about eight years after menarche. That deliberately trades a premature label for a scheduled second look.

Ruling out the mimics

Because these features overlap with other conditions, the diagnosis is one of pattern plus exclusion. When androgen levels sit markedly above the laboratory reference range, the guideline directs clinicians to consider causes other than PCOS, including androgen-secreting tumors, non-classic congenital adrenal hyperplasia, and Cushing's syndrome. Thyroid disease and elevated prolactin are also checked, since both can disrupt cycles. PCOS is what remains after those alternatives are addressed, which is why no single result, AMH included, can carry the diagnosis by itself.