Getting diagnosed with polycystic ovary syndrome (PCOS) requires meeting at least two out of three specific criteria: irregular or absent periods, elevated androgen hormones, and polycystic-appearing ovaries on ultrasound. There is no single test that confirms PCOS on its own. Instead, diagnosis involves a combination of symptom evaluation, blood work, and sometimes imaging, along with ruling out other conditions that look similar.
The Three Diagnostic Criteria
The most widely used framework for diagnosing PCOS is the Rotterdam criteria, which requires you to meet at least two of these three features:
- Irregular ovulation or periods. This typically means cycles longer than 35 days apart, or fewer than 8 periods per year. Complete absence of periods also counts.
- High androgen levels. This can be confirmed through blood tests showing elevated hormones, or through visible signs like excess hair growth, acne, or hair thinning.
- Polycystic ovarian morphology. This means your ovaries show a specific pattern on ultrasound: 20 or more small follicles in at least one ovary, or an ovarian volume of 10 mL or greater.
You don’t need all three. Someone with irregular periods and elevated testosterone but normal-looking ovaries on ultrasound still qualifies. Someone with polycystic ovaries and excess hair growth but regular periods also qualifies.
What Happens at the Appointment
Your doctor will start with a detailed history of your menstrual cycles, weight changes, skin changes, and any difficulty getting pregnant. They’ll likely examine your skin for acne, excess hair growth, and dark patches that can signal insulin resistance. Hair growth is sometimes scored using a standardized chart called the Ferriman-Gallwey scale, which rates hair density across nine body areas. A score of 8 or higher is considered clinical hirsutism.
From there, you’ll typically get blood work and possibly an ultrasound. The goal is both to check for the diagnostic criteria and to rule out other conditions that cause similar symptoms.
Blood Tests You Can Expect
The blood panel for PCOS evaluation usually covers several hormones. Testosterone is the most important androgen measured, and levels roughly double in women with PCOS compared to those without. Your doctor may also check androstenedione (another androgen), DHEAS (an androgen produced by the adrenal glands), and a ratio of two brain hormones called LH and FSH. When the LH-to-FSH ratio is higher than about 1.2, it supports a PCOS diagnosis.
Anti-Müllerian hormone (AMH) has become increasingly useful. The 2023 international evidence-based guidelines now allow AMH blood testing as an alternative to ultrasound in adults. AMH is produced by the small follicles in the ovaries, so elevated levels reflect the same ovarian pattern that ultrasound would show, without needing the scan.
Sex hormone-binding globulin (SHBG) is another marker that often comes back low in PCOS. This protein normally binds to testosterone and keeps it inactive. When SHBG drops, more testosterone circulates freely, which drives symptoms like acne and hair growth even when total testosterone looks borderline normal. That’s why some doctors also calculate a “free androgen index” from your testosterone and SHBG levels.
Insulin and Metabolic Screening
Insulin resistance isn’t part of the formal diagnostic criteria, but it affects a large proportion of people with PCOS and shapes treatment decisions. Many doctors will order a fasting glucose and insulin level, or a two-hour oral glucose tolerance test where you drink a sugary solution and have your blood drawn before and after. The glucose tolerance test remains the most reliable way to catch impaired glucose metabolism, though it takes longer and is less convenient than a simple fasting blood draw.
Some providers calculate a score called HOMA-IR from your fasting insulin and glucose. A value above 2.0 is commonly used to indicate insulin resistance. This doesn’t diagnose PCOS itself, but it helps your doctor understand your metabolic risk and decide whether treatments targeting insulin resistance would benefit you.
Ultrasound: What It Shows
A pelvic ultrasound (often transvaginal for better image quality) looks at the size and appearance of your ovaries. The current threshold for polycystic morphology is 20 or more follicles measuring 2 to 9 mm in at least one ovary, or an ovarian volume of 10 mL or more. If the imaging equipment is older or image quality is limited, a count of 10 or more follicles per cross-section is an acceptable alternative.
It’s worth knowing that “polycystic ovaries” on ultrasound doesn’t mean you have cysts in the traditional sense. These are small, fluid-filled follicles that are a normal part of ovarian function. In PCOS, there are simply more of them than usual, and they tend to stay small rather than maturing and releasing an egg.
Not everyone needs an ultrasound. If you already meet the other two criteria (irregular periods plus high androgens), the diagnosis is established without imaging.
Conditions That Must Be Ruled Out First
PCOS is technically a diagnosis of exclusion, meaning your doctor needs to confirm that your symptoms aren’t caused by something else. Several conditions mimic PCOS closely:
- Non-classical congenital adrenal hyperplasia (NCAH). This genetic condition causes the adrenal glands to overproduce androgens. It’s distinguished from PCOS by measuring a hormone called 17-OH progesterone, sometimes with a stimulation test.
- Thyroid disorders. Both overactive and underactive thyroid can disrupt periods and cause hair or skin changes.
- High prolactin levels. Elevated prolactin (sometimes from a small pituitary growth) can stop ovulation and mimic PCOS symptoms.
- Cushing’s syndrome. Excess cortisol production causes weight gain, irregular periods, and acne. A dexamethasone suppression test is used to differentiate this from PCOS.
- Androgen-producing tumors. Rare, but rapidly worsening virilization (deepening voice, significant muscle changes) warrants investigation.
Most of these can be screened with the same blood draw used to check your androgen levels, so ruling them out doesn’t usually require separate appointments.
Diagnosis in Teenagers
PCOS is harder to diagnose during adolescence because the hallmark features overlap with normal puberty. Irregular periods are common in the first few years after a girl’s first period, and ovaries naturally appear “polycystic” during this stage of development.
For this reason, current guidelines recommend against using ultrasound to diagnose PCOS in adolescents. Instead, diagnosis in teens requires both irregular cycles and confirmed hyperandrogenism (elevated androgens on blood work or clear clinical signs like significant hirsutism or persistent acne). Meeting just one criterion isn’t enough.
The definition of “irregular” also shifts for younger patients. In the first one to three years after menarche, cycles shorter than 21 days or longer than 45 days are considered concerning. A gap of more than 90 days between periods at any point after menarche, or not getting a first period by age 15, also raises suspicion. Because so many healthy teens have irregular cycles while still ovulating normally, doctors are cautious about labeling someone with PCOS too early. When the picture is unclear, guidelines suggest monitoring and reassessing over time rather than rushing to a firm diagnosis.
Which Doctors Diagnose PCOS
Your primary care doctor or general practitioner can start the workup and, in straightforward cases, make the diagnosis. For more complex situations, you may be referred to a gynecologist, an endocrinologist (hormone specialist), or a reproductive endocrinologist if fertility is a concern. Endocrinologists are particularly helpful when the distinction between PCOS and adrenal disorders is unclear, or when metabolic issues like insulin resistance need closer management.
If your first doctor dismisses your symptoms or attributes them solely to weight, it’s reasonable to seek a second opinion. PCOS occurs across all body sizes, and delayed diagnosis is common, particularly for people whose symptoms are milder or who don’t fit the “classic” presentation.