How is polycystic ovary syndrome (PCOS) diagnosed in a woman of reproductive age?

How to Diagnose PCOS

Diagnose PCOS using the Rotterdam criteria: at least 2 of 3 features must be present—(1) oligo- or anovulation, (2) clinical and/or biochemical hyperandrogenism, and (3) polycystic ovarian morphology on ultrasound—after excluding other causes of hyperandrogenism and ovulatory dysfunction. 1, 2

Step 1: Clinical Assessment

History

Document the following specific features:

• Menstrual pattern: Cycle length >35 days suggests chronic anovulation; oligomenorrhea is the most common abnormal pattern in PCOS 1, 3
• Onset and duration of signs of androgen excess (acne, hirsutism, male-pattern balding) 4
• Medication use, particularly exogenous androgens 1
• Family history of cardiovascular disease, diabetes, and PCOS 4, 1
• Lifestyle factors: diet, exercise patterns, alcohol use, smoking 4, 1

Physical Examination

Look for these specific findings:

• Hyperandrogenism signs: acne, male-pattern balding, hirsutism (document distribution), clitoromegaly 4
• Insulin resistance markers: obesity, acanthosis nigricans (neck, axillae, beneath breasts, vulva) 4
• Calculate BMI and waist-hip ratio 4, 1
• Pelvic examination for ovarian enlargement 4

Step 2: Laboratory Testing to Confirm Hyperandrogenism

Order total testosterone measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS)—this is the single best initial test with 74% sensitivity and 86% specificity. 1, 5

Additional androgen testing:

• Calculated free testosterone using the Vermeulen equation has the highest sensitivity at 89% with 83% specificity 1, 5
• Free androgen index (FAI): 78% sensitivity, 85% specificity (use cautiously when SHBG <30 nmol/L) 1
• Androstenedione: 75% sensitivity, 71% specificity; useful when SHBG is low 1
• DHEAS: 75% sensitivity, 67% specificity; most reliable for adrenal androgen production, particularly in women <30 years 1

Critical pitfall: Do not use direct immunoassays—they have inferior accuracy compared to LC-MS/MS. 1, 5 Hormonal contraception (including progestin-only implants like Implanon) suppresses the hypothalamic-pituitary-ovarian axis and makes hormone levels unreliable; remove or allow to expire before testing. 1

Step 3: Ultrasound Assessment

Use transvaginal ultrasound with ≥8 MHz transducer frequency in adults. 1, 6

Diagnostic thresholds for polycystic ovarian morphology:

• ≥20 follicles per ovary (2-9mm diameter) is the gold standard: 87.64% sensitivity, 93.74% specificity 1, 6
• Ovarian volume >10 mL is an alternative when accurate follicle counting is difficult 1, 6

Age-specific caution: Do not use ultrasound as a first-line diagnostic tool in adolescents <8 years post-menarche or <20 years old due to poor specificity and high false-positive rates from normal multifollicular ovaries. 1 In adolescents, require all three Rotterdam criteria plus 2-3 years of persistent symptoms beyond menarche before diagnosing PCOS. 1

Important caveat: Up to one-third of reproductive-aged women without PCOS have polycystic ovarian morphology on ultrasound, so ultrasound findings alone are insufficient for diagnosis. 1 The presence of an IUD does not interfere with ovarian imaging. 6

Step 4: Exclude Other Diagnoses

You must rule out these conditions before confirming PCOS:

Mandatory screening tests:

• TSH to exclude thyroid disease 4, 1
• Prolactin (morning, resting level) to rule out hyperprolactinemia—women with PCOS have 3.15-fold increased risk of elevated prolactin 4, 1

Screen for these conditions based on clinical features:

• Cushing's syndrome if buffalo hump, moon facies, hypertension, abdominal striae, centripetal fat distribution, easy bruising, or proximal myopathy present 4
• Androgen-secreting tumors if rapid onset and severe virilization (marked clitoromegaly, deepening voice) 4, 1
• Non-classic congenital adrenal hyperplasia 4, 1
• Acromegaly if appropriate clinical features 4

Critical pitfall: In women with acanthosis nigricans, consider associated insulinoma or gastric adenocarcinoma. 4

Step 5: Metabolic Screening (All Women with PCOS)

Screen all women with PCOS for metabolic complications regardless of BMI, as insulin resistance occurs independently of body weight. 1

Required screening:

• 2-hour oral glucose tolerance test with 75-gram glucose load (fasting glucose followed by 2-hour post-load glucose) to screen for type 2 diabetes and glucose intolerance 4, 1
• Fasting lipid profile: total cholesterol, LDL, HDL, triglycerides 4, 1

Special Considerations

Anti-Müllerian hormone (AMH) is NOT recommended for clinical diagnosis despite being elevated in PCOS—there is no standardization across assays, no validated cut-offs, significant overlap between women with and without PCOS, and age-dependent variability. 1

Transient multifollicular appearance can occur after discontinuing birth control and does not represent true PCOS. 1 Similarly, excessive exercise (e.g., twice daily, 6 days/week) can cause hypothalamic suppression and amenorrhea, mimicking PCOS. 1