Polycystic ovary syndrome (PCOS) is diagnosed using a set of criteria called the Rotterdam criteria, which require you to have at least two of three key features: irregular or absent ovulation, signs of excess androgens (often called “male hormones”), or polycystic-appearing ovaries on ultrasound. There is no single blood test or scan that confirms PCOS on its own. Instead, diagnosis involves a combination of your medical history, physical exam, blood work, and sometimes imaging, along with ruling out other conditions that can look similar.
The Three Diagnostic Criteria
The Rotterdam criteria remain the international standard for diagnosing PCOS. You need to meet at least two of the following three criteria, and other conditions that could explain your symptoms must be excluded first.
Irregular or absent ovulation. This typically shows up as irregular periods, meaning cycles that are consistently shorter than 21 days or longer than 35 days. Some people skip periods entirely for months at a time, or have fewer than eight cycles per year. These patterns suggest your ovaries aren’t regularly releasing eggs.
Excess androgens. This can be identified either through physical signs (called clinical hyperandrogenism) or through blood tests (biochemical hyperandrogenism). Physical signs include excess hair growth on the face, chest, or abdomen, persistent acne, and thinning hair on the scalp. On blood work, elevated testosterone or a high free androgen index confirms this criterion. Notably, testosterone levels can be normal in some people with PCOS, so a normal result alone doesn’t rule it out.
Polycystic ovarian morphology. On ultrasound, the ovaries may appear enlarged or contain a high number of small follicles arranged around the outer edge. Despite the name, these aren’t true cysts. They’re small, fluid-filled sacs containing immature eggs. An ovarian volume above 10 milliliters on either ovary can also meet this criterion.
What Happens During the Physical Exam
Your provider will look for visible signs of excess androgens. The most common is hirsutism, which means coarse, dark hair growing in areas where it’s typically minimal in women, like the upper lip, chin, chest, lower abdomen, and back. Clinicians assess hirsutism using a standardized visual scoring system called the modified Ferriman-Gallwey scale, which rates hair growth across nine body areas from 0 (none) to 4 (extensive). A total score of 8 or higher is considered hirsutism. Scores of 8 to 16 indicate mild hirsutism, 17 to 24 moderate, and above 24 severe.
Your provider will also check for acne, hair thinning at the crown, and signs of insulin resistance like dark, velvety patches of skin on the neck or underarms (called acanthosis nigricans). They may ask detailed questions about your menstrual history, including how long your cycles last and how many periods you’ve had in the past year.
Blood Tests Used in Diagnosis
Blood work serves two purposes: confirming androgen levels and ruling out other conditions. A total testosterone level is the most reliable androgen measurement. Most testosterone values in PCOS fall at or below 150 ng/dL. Values of 200 ng/dL or higher raise concern for an ovarian or adrenal tumor and require further investigation. If you’ve been on hormonal birth control, your provider may ask you to stop it for three months before testing, since oral contraceptives lower testosterone and can mask true levels.
Other blood tests typically include thyroid function (to rule out thyroid disease), prolactin (to rule out a pituitary issue), and a test for a hormone called 17-hydroxyprogesterone, which screens for a genetic adrenal condition called late-onset congenital adrenal hyperplasia. These conditions can cause irregular periods and excess hair growth, mimicking PCOS. A fasting glucose-to-insulin ratio may also be checked. A ratio below 4.5 suggests insulin resistance, which is common in PCOS but is not one of the three formal diagnostic criteria.
The Role of Ultrasound
A pelvic ultrasound, usually transvaginal for the clearest view, looks at ovarian size and follicle count. If the ovaries show a characteristic “string of pearls” appearance with many small follicles, or if ovarian volume is enlarged, this meets the polycystic morphology criterion. It’s worth knowing that having polycystic-appearing ovaries alone does not mean you have PCOS. Up to a quarter of women without any symptoms have this appearance on ultrasound. The finding only becomes diagnostically relevant when paired with at least one of the other two criteria.
Ultrasound is not always required. If you already meet the other two criteria (irregular cycles plus excess androgens), imaging is unnecessary to confirm the diagnosis.
How Diagnosis Differs for Teenagers
Diagnosing PCOS in adolescents is trickier because irregular periods and acne are common during normal puberty. The 2018 international PCOS guideline addressed this by recommending stricter criteria for teenagers: both irregular ovulation and clinical or biochemical hyperandrogenism must be present. Ultrasound of the ovaries is not recommended for adolescent diagnosis, since polycystic ovarian morphology is a normal finding during the teenage years and doesn’t reliably indicate PCOS in this age group.
Teens who have only one of the two required features, like persistent irregular cycles without androgen excess, are considered “at risk” for PCOS rather than diagnosed with it. Guidelines recommend reassessing these individuals once they reach adulthood, when the diagnostic criteria become clearer.
Four Recognized Phenotypes
Because the diagnosis requires only two of three criteria, PCOS can look quite different from person to person. Researchers classify these into four phenotypes:
- Phenotype A includes all three features: excess androgens, irregular ovulation, and polycystic ovaries. This is the most common presentation, accounting for roughly 68% of cases in clinical studies.
- Phenotype B includes excess androgens and irregular ovulation but normal-appearing ovaries on ultrasound. About 11% of cases fall here.
- Phenotype C includes excess androgens and polycystic ovaries, but ovulation is regular. This makes up about 18% of cases.
- Phenotype D includes irregular ovulation and polycystic ovaries without elevated androgens. This is the least common, at around 4% of cases.
These phenotypes matter because they come with different metabolic risk profiles. Phenotypes A and B, which both involve androgen excess and ovulatory problems, tend to carry higher risks for insulin resistance and cardiovascular issues. Phenotype D, without androgen excess, generally has a milder metabolic profile.
AMH as an Emerging Diagnostic Tool
Anti-Müllerian hormone (AMH) is produced by the small follicles in the ovaries, and levels tend to be significantly elevated in people with PCOS. A 2025 systematic review in the American Journal of Obstetrics and Gynecology concluded that AMH can serve as a diagnostic marker for PCOS when factors like age, body mass index, and PCOS phenotype are taken into account. This is particularly useful when ultrasound isn’t practical or accessible, such as in adolescents or when a transvaginal scan isn’t possible. For now, guidelines recommend AMH as a supplementary tool rather than a replacement for the established Rotterdam criteria.
Insulin Resistance and Metabolic Screening
Insulin resistance is extremely common in PCOS, but it is not part of the formal diagnostic criteria. Your body produces insulin normally, but your cells don’t respond to it efficiently, which forces the pancreas to produce more. Over time, this raises the risk of type 2 diabetes. The CDC recommends that anyone diagnosed with PCOS ask about screening for type 2 diabetes. This typically involves a fasting glucose test or an oral glucose tolerance test, where your blood sugar is measured before and two hours after drinking a sugary solution. Even if your fasting glucose looks normal, the glucose tolerance test can catch early insulin resistance that a single fasting number might miss.