How Is PCOS Diagnosed? What the Workup Actually Looks Like

What the diagnostic criteria actually require

The most widely used framework — the Rotterdam criteria — requires at least two of the following three features, after other conditions have been excluded 1Ref 1American College of Obstetricians and Gynecologists (2018).ACOG Practice Bulletin No. 194: Polycystic Ovary Syndrome.Rotterdam diagnostic criteria requiring two of three features, the role of androgen testing, ultrasound, and the exclusion-first approach to PCOS diagnosis.:

1. Irregular ovulation — infrequent periods, long cycles (more than 35 days), or no periods at all. 2. Signs of excess androgen — either measured in blood (elevated testosterone or DHEAS) or visible physically (significant acne, noticeable dark or coarse hair on the face or body, or scalp thinning in a male pattern). 3. Polycystic-appearing ovaries on ultrasound — a higher-than-normal number of small follicles per ovary, or increased ovarian volume.

Importantly, ultrasound alone is not diagnostic and that pattern can appear in people without PCOS. The name itself is somewhat misleading: the 'cysts' here are undeveloped follicles, not true cysts, and many people with PCOS never have a classic ovarian cyst.

What blood tests are typically ordered — and why

Blood work serves two purposes: it measures hormone levels directly and screens for conditions that mimic PCOS 1Ref 1American College of Obstetricians and Gynecologists (2018).ACOG Practice Bulletin No. 194: Polycystic Ovary Syndrome.Rotterdam diagnostic criteria requiring two of three features, the role of androgen testing, ultrasound, and the exclusion-first approach to PCOS diagnosis..

• Androgens (total and free testosterone, sometimes DHEAS or androstenedione) — to objectively confirm hormonal excess, since physical signs vary widely.
• TSH — thyroid dysfunction, both underactive and overactive, commonly disrupts the menstrual cycle and can look identical to PCOS. It is a standard early exclusion 2Ref 2Jonklaas J, Bianco AC, Bauer AJ, et al. (2014).Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement.Thyroid dysfunction as a common cause of menstrual irregularity that must be excluded before attributing symptoms to PCOS; rationale for TSH testing in the workup..
• Prolactin — elevated prolactin from a benign pituitary growth can stop periods; ruled out with a single blood test.
• 17-hydroxyprogesterone — to screen for non-classic congenital adrenal hyperplasia, a less common but important mimic that requires a different treatment path.
• Fasting glucose, fasting insulin, or HbA1c — insulin resistance is very common in PCOS and carries independent health consequences 3Ref 3American Diabetes Association Professional Practice Committee (2024).Standards of Care in Diabetes—2024.Clinical significance of insulin resistance testing in PCOS and the independent health consequences of unmanaged blood sugar.. A 2024 update from the American Diabetes Association notes that insulin-related testing is clinically meaningful even when formal diabetes criteria are not met 3Ref 3American Diabetes Association Professional Practice Committee (2024).Standards of Care in Diabetes—2024.Clinical significance of insulin resistance testing in PCOS and the independent health consequences of unmanaged blood sugar..
• Lipid panel — PCOS is associated with an unfavorable lipid profile; a baseline is useful for cardiovascular risk monitoring 4Ref 4Grundy SM, Stone NJ, Bailey AL, et al. (2019).2018 AHA/ACC/AACVPR/AAPA/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA Guideline on the Management of Blood Cholesterol.Rationale for lipid panel as part of PCOS workup given the elevated cardiovascular risk associated with the condition..

Not every clinician orders all of these at once. The specific panel depends on your symptoms, weight, and family history.

What role does ultrasound play?

A pelvic ultrasound — usually transvaginal for the clearest view — can show the characteristic follicle pattern of PCOS. Guidelines specify thresholds for follicle count and ovarian volume, though these numbers vary by guideline version and equipment used, because ultrasound technology has improved since the original Rotterdam criteria were written 1Ref 1American College of Obstetricians and Gynecologists (2018).ACOG Practice Bulletin No. 194: Polycystic Ovary Syndrome.Rotterdam diagnostic criteria requiring two of three features, the role of androgen testing, ultrasound, and the exclusion-first approach to PCOS diagnosis..

Ultrasound is not mandatory if both other criteria are already present (irregular cycles and androgen signs or levels). A normal ultrasound does not rule out PCOS.

What conditions does the workup need to rule out first?

PCOS is a diagnosis of exclusion as much as inclusion. Before attributing symptoms to PCOS, a clinician will want to exclude:

• Thyroid disease — both hypothyroidism and hyperthyroidism disrupt cycle regularity and can cause fatigue, weight changes, hair loss, and mood symptoms that overlap substantially with PCOS 2Ref 2Jonklaas J, Bianco AC, Bauer AJ, et al. (2014).Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement.Thyroid dysfunction as a common cause of menstrual irregularity that must be excluded before attributing symptoms to PCOS; rationale for TSH testing in the workup..
• Elevated prolactin (hyperprolactinemia) — a pituitary cause of stopped or irregular periods; galactorrhea (milky nipple discharge) may be a clue.
• Non-classic congenital adrenal hyperplasia — produces excess androgen from the adrenal glands rather than the ovaries; can present identically to PCOS but has a different management path.
• Insulin resistance or metabolic syndrome without PCOS — weight gain, dark skin patches in folds (acanthosis nigricans), and a family history of diabetes are relevant contextual findings.

If you are currently using hormonal contraception, your clinician may note that pills, patches, and the hormonal IUD regulate periods and suppress androgen levels — masking PCOS signs while in use. A complete diagnostic picture may require waiting several months after stopping hormonal contraception before interpreting results.

What happens after a PCOS diagnosis?

Diagnosis is the beginning of an ongoing conversation, not a finish line. PCOS affects people differently — some are most concerned about irregular periods, others about acne or unwanted hair, others about fertility or metabolic health. Management is tailored to what matters most right now, and those priorities change over time.

A clinician will also monitor for associated conditions including insulin resistance, elevated blood pressure, and mood changes, which are more common in people with PCOS. Annual or periodic screening for blood sugar and lipids is part of long-term care, given the elevated cardiovascular and metabolic risk 3Ref 3American Diabetes Association Professional Practice Committee (2024).Standards of Care in Diabetes—2024.Clinical significance of insulin resistance testing in PCOS and the independent health consequences of unmanaged blood sugar.4Ref 4Grundy SM, Stone NJ, Bailey AL, et al. (2019).2018 AHA/ACC/AACVPR/AAPA/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA Guideline on the Management of Blood Cholesterol.Rationale for lipid panel as part of PCOS workup given the elevated cardiovascular risk associated with the condition..

Any discussion of fertility should happen early if conception is a goal — PCOS is a leading cause of ovulatory infertility, but effective treatments exist, and early planning matters.