What are the diagnostic criteria and methods for diagnosing Polycystic Ovary Syndrome (PCOS)?

How to Diagnose PCOS

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

Core Diagnostic Criteria

The Rotterdam criteria require any 2 of the following 3 features for diagnosis 1, 2, 3:

• Oligo- or anovulation: Menstrual cycle length >35 days indicates chronic anovulation; cycles between 32-35 days or slightly irregular patterns warrant assessment for ovulatory dysfunction 1, 2
• Clinical or biochemical hyperandrogenism: Look for hirsutism (gradual onset, intensifies with weight gain), acne (especially severe or treatment-resistant), male-pattern alopecia (vertex, crown, or diffuse pattern), or elevated androgen levels 1, 2
• Polycystic ovarian morphology (PCOM): Defined as ≥20 follicles per ovary (2-9 mm in size) or ovarian volume >10 mL on ultrasound 1, 2

Clinical Assessment

History Taking

Document the following specific elements 1:

• Onset and duration of androgen excess signs (hirsutism, acne, hair loss)
• Menstrual history: Cycle length, regularity, age at menarche
• Medication use: Exogenous androgens or hormonal therapies
• Lifestyle factors: Diet, exercise habits, alcohol use, smoking
• Family history: Cardiovascular disease, diabetes, PCOS

Physical Examination

Assess for these specific findings 1, 2:

• Hyperandrogenism signs: Hirsutism (use Ferriman-Gallwey score), acne distribution, male-pattern balding, clitoromegaly (suggests virilizing tumor if present)
• Body habitus: Calculate BMI and waist-hip ratio
• Cushing's features: Buffalo hump, moon facies, abdominal striae, hypertension (to exclude Cushing's syndrome) 1

Laboratory Evaluation

First-Line Hormonal Testing

• Free testosterone: More sensitive than total testosterone for detecting androgen excess; use equilibrium dialysis method for accuracy 2
• Total testosterone: Useful but less sensitive than free testosterone 2
• 17-hydroxyprogesterone (17-OHP): Measure to exclude non-classic congenital adrenal hyperplasia (NCCAH); elevated basal or ACTH-stimulated levels suggest NCCAH 1, 4
• TSH and prolactin: Rule out thyroid disease and hyperprolactinemia, which can mimic PCOS 1, 4

Additional Testing When Indicated

• DHEA-sulfate: If very elevated (>700 mcg/dL) or rapid-onset severe hyperandrogenism, consider androgen-secreting tumor 4, 5
• 24-hour urinary free cortisol or overnight dexamethasone suppression test: If clinical signs of hypercortisolism present 1, 4

Ultrasound Assessment

In Adults (≥18 years)

• Use transvaginal ultrasound with ≥8 MHz transducer frequency for optimal resolution 1
• Follicle number per ovary (FNPO) ≥20 follicles is the gold standard marker with 87.64% sensitivity and 93.74% specificity 6, 1
• Alternative markers when accurate follicle counting is not possible: ovarian volume >10 mL or follicle number per single cross-section (FNPS) 6, 1

In Adolescents (<20 years, ≥1 year post-menarche)

• Avoid ultrasound as first-line investigation in those <17 years due to poor specificity and high false-positive rates 1, 2
• Rely on clinical and biochemical hyperandrogenism plus menstrual irregularity persisting >2-3 years post-menarche 1, 2
• Large multicystic ovaries are common normal findings in adolescents 2

Differential Diagnosis to Exclude

Before confirming PCOS, rule out these conditions 1, 4:

• Non-classic congenital adrenal hyperplasia (NCCAH): Elevated 17-OHP (basal or ACTH-stimulated); significant decrease in testosterone and DHEA-S with 2-day dexamethasone suppression test 4
• Cushing's syndrome: Buffalo hump, moon facies, hypertension, abdominal striae; screen with overnight dexamethasone suppression test or 24-hour urinary free cortisol 1, 4
• Androgen-secreting tumors: Rapid onset, severe hyperandrogenism, virilization (clitoromegaly), very high serum androgens 1, 4
• Hyperprolactinemia: Recent onset oligomenorrhea with mild hyperandrogenism 4
• Thyroid disease: Check TSH 1
• Primary ovarian failure: Consider in appropriate clinical context 1

Important Diagnostic Pitfalls

Medication Interference

If the patient is taking spironolactone or oral contraceptives, these medications can mask diagnostic features 7:

• Spironolactone lowers testosterone levels and improves hirsutism, potentially concealing biochemical and clinical hyperandrogenism 7
• Ideally, perform PCOS evaluation before initiating these therapies 7
• If already on medication, consider a 2-4 week washout period before hormonal evaluation 7
• If washout is not possible, place greater emphasis on ultrasound findings of PCOM, which are less affected by these medications 7

Age-Specific Considerations

• In adolescents, menstrual irregularities and anovulatory cycles are common for 2-3 years post-menarche due to hypothalamic-pituitary-ovarian axis immaturity; persistent oligomenorrhea beyond this period predicts ongoing dysfunction 2
• Testosterone assay sensitivity is limited in the ranges applicable to young girls 2

Metabolic Screening After Diagnosis

Once PCOS is diagnosed, screen for metabolic complications 1, 8:

• Screen all women with PCOS for type 2 diabetes and glucose intolerance 1
• Fasting lipid profile to assess for dyslipidemia 1
• Screen for depression and obstructive sleep apnea, as these are increased in PCOS 8