Diagnostic Criteria for Polycystic Ovary Syndrome (PCOS)
PCOS is diagnosed when at least two of the following three Rotterdam criteria are present: (1) oligo- or anovulation, (2) clinical and/or biochemical hyperandrogenism, and (3) polycystic ovarian morphology on ultrasound—after excluding other relevant disorders. 1, 2, 3
Core Diagnostic Framework
The Rotterdam criteria require meeting any 2 of 3 features 1, 4:
- Oligo- or anovulation: Menstrual cycle length >35 days indicates chronic anovulation 1, 4
- Hyperandrogenism: Either clinical signs (hirsutism, acne, balding, clitoromegaly) or biochemical elevation of androgens 1, 4
- Polycystic ovarian morphology (PCOM): Specific ultrasound findings detailed below 1, 3
This creates multiple phenotypes: women with all three features, those with hyperandrogenism and PCOM but regular cycles, and those with ovulatory dysfunction and PCOM without hyperandrogenism 2, 5.
Clinical Assessment Components
History and Physical Examination
- Menstrual history: Document cycle length, with >35 days suggesting chronic anovulation; cycles 32-35 days require assessment for ovulatory dysfunction 1, 4
- Androgen excess timeline: Evaluate onset and duration; rapid onset with severe hyperandrogenism suggests androgen-secreting tumors rather than PCOS 1, 4
- Hyperandrogenism signs: Look for acne (particularly severe or isotretinoin-resistant), hirsutism (gradual onset, worsens with weight gain), balding (vertex/crown/diffuse pattern, or bitemporal with frontal hairline loss in severe cases), and clitoromegaly 1, 4
- Medication review: Document use of exogenous androgens 1
- Lifestyle factors: Assess diet, exercise patterns (excessive exercise can cause hypothalamic amenorrhea mimicking PCOS), alcohol use, and smoking 1
- Family history: Obtain history of cardiovascular disease and diabetes 1
- Anthropometric measurements: Calculate BMI and waist-hip ratio 1, 4
Laboratory Testing for Hyperandrogenism
Total testosterone (TT) measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS) is the single best initial biochemical marker, with 74% sensitivity and 86% specificity. 1, 4
Additional androgen testing options 1, 4:
- Calculated free testosterone (cFT): Highest sensitivity at 89% with 83% specificity; calculate using the Vermeulen equation from high-quality TT and SHBG measurements 1
- Free androgen index (FAI): 78% sensitivity and 85% specificity, but use cautiously when SHBG <30 nmol/L 1
- Androstenedione (A4): 75% sensitivity and 71% specificity; useful when SHBG is low 1
- DHEAS: 75% sensitivity and 67% specificity; most reliable for adrenal androgen production, particularly valuable in women <30 years 1
LC-MS/MS offers superior specificity (92% vs 78%) and sensitivity (71% vs 74%) compared to immunoassays 1.
Ultrasound Criteria for PCOM
Use transvaginal ultrasound with ≥8 MHz transducer frequency in adults for optimal resolution. 1, 6, 4
Gold standard marker: Follicle number per ovary (FNPO) ≥20 follicles measuring 2-9mm diameter, with 87.64% sensitivity and 93.74% specificity 1, 6, 4
Alternative markers when accurate follicle counting is impossible 1, 6:
- Document three dimensions and volume of each ovary
- Ensure no corpora lutea, cysts, or dominant follicles ≥10mm are present
- Report total follicle number per ovary measuring 2-9mm
- If transvaginal approach is unacceptable, transabdominal ultrasound focusing on ovarian volume ≥10mL can be used, though follicle counting is less reliable
Age-Specific Diagnostic Considerations
Adolescents (<20 years, at least 1 year post-menarche)
Do not use ultrasound as a first-line diagnostic tool in adolescents due to poor specificity and high false-positive rates. 1, 6, 4
- Menstrual irregularities and anovulatory cycles are common in the 2-3 years post-menarche due to hypothalamic-pituitary-ovarian axis immaturity 4
- Persistent oligomenorrhea 2-3 years beyond menarche predicts ongoing menstrual irregularities and greater likelihood of PCOS 1, 4
- Rely on clinical and biochemical hyperandrogenism plus menstrual irregularity persisting 2-3 years beyond menarche 1, 4
- Large, multicystic ovaries are common findings in normal adolescents 4
- Testosterone assays have major sensitivity limitations in ranges applicable to young girls 4
Adults (18-50 years)
Full Rotterdam criteria apply, and transvaginal ultrasound is appropriate and recommended 1.
Critical Differential Diagnoses to Exclude
Before confirming PCOS, rule out 1:
- Cushing's syndrome: Buffalo hump, moon facies, hypertension, abdominal striae 1
- Androgen-secreting tumors (ovary or adrenal): Rapid onset and severe hyperandrogenism, often with clitoromegaly 1, 4
- Non-classic congenital adrenal hyperplasia: Measure 17-hydroxyprogesterone 1
- Thyroid disease and prolactin disorders: Check TSH and prolactin 1
- Primary hypothalamic amenorrhea: Consider excessive exercise patterns (e.g., working out twice daily, 6 days/week) causing hypothalamic suppression 1
- Primary ovarian failure: Check FSH 1
- Acromegaly and genetic defects in insulin action 1
Important Clinical Pitfalls
- Polycystic ovarian morphology alone is insufficient for diagnosis: Up to one-third of reproductive-aged women without PCOS have PCOM on ultrasound 1
- Transient multifollicular appearance can occur during recovery after discontinuing birth control and does not represent true PCOS 1
- IUD presence does not interfere with ovarian imaging: The IUD sits within the endometrial cavity while ovaries are separate lateral pelvic structures 6
- Ultrasound should not be used <8 years post-menarche due to high incidence of multifollicular ovaries in this life stage 6, 4
- AMH should not replace Rotterdam criteria: Despite elevated levels (2-3 times higher) in PCOS, significant assay variability, lack of standardization, and overlap with normal women limit its diagnostic utility outside research settings 8
Required Metabolic Screening After PCOS Diagnosis
Once PCOS is diagnosed, perform comprehensive metabolic screening 1, 8, 7: