What conditions need to be excluded and what tests are required to diagnose Polycystic Ovary Syndrome (PCOS)?

Conditions to Exclude and Required Tests for PCOS Diagnosis

PCOS is a diagnosis of exclusion requiring systematic evaluation to rule out thyroid disease, hyperprolactinemia, non-classical congenital adrenal hyperplasia, Cushing's syndrome, and androgen-secreting tumors before confirming the diagnosis. 1, 2, 3

Mandatory Conditions to Exclude

Thyroid Disease

• Measure thyroid-stimulating hormone (TSH) to rule out thyroid dysfunction as a cause of menstrual irregularity 1, 2
• Thyroid disorders commonly mimic PCOS with oligomenorrhea and weight changes 4

Hyperprolactinemia

• Measure morning resting serum prolactin levels (not post-ictal), with levels >20 μg/L considered abnormal 4, 1, 2
• Mild elevations can occur in epilepsy patients; rule out pituitary tumors if significantly elevated 4
• Recent onset oligomenorrhea with mild hyperandrogenism should always prompt prolactin testing 3

Non-Classical Congenital Adrenal Hyperplasia (NCCAH)

• Measure early morning 17-hydroxyprogesterone (17-OHP) between days 3-6 of menstrual cycle 2, 3
• If basal 17-OHP is elevated, perform ACTH stimulation test for confirmation 3
• Measure DHEAS levels, with age-specific cutoffs: >3800 ng/mL (age 20-29) or >2700 ng/mL (age 30-39) suggesting NCCAH 4, 1
• Alternative approach: two-day dexamethasone suppression test showing significant decrease in testosterone and DHEAS confirms NCCAH 3

Cushing's Syndrome

• Screen if patient exhibits: buffalo hump, moon facies, hypertension, abdominal striae, central fat distribution, easy bruising, or proximal myopathies 1, 2
• Perform overnight dexamethasone suppression test or measure 24-hour urinary free cortisol 3, 5
• Consider especially with recent onset hyperandrogenism and signs of hypercortisolism 3

Androgen-Secreting Tumors (Ovarian or Adrenal)

• Suspect if: rapid onset of symptoms, severe hirsutism, virilization, or very high testosterone levels 1, 2, 3
• Measure androstenedione, with levels >10.0 nmol/L indicating possible adrenal/ovarian tumor 4, 1
• Measure total testosterone using LC-MS/MS; markedly elevated levels (typically >150-200 ng/dL) warrant imaging 1, 5
• Severe virilization (clitoromegaly, voice deepening, male-pattern baldness) mandates immediate tumor exclusion 3, 5

Core Diagnostic Laboratory Tests for PCOS

Androgen Assessment (First-Line)

• Measure total testosterone AND free testosterone using liquid chromatography-tandem mass spectrometry (LC-MS/MS) 1, 2
• Total testosterone shows 74% sensitivity and 86% specificity; free testosterone demonstrates superior 89% sensitivity with 83% specificity 1
• LC-MS/MS is mandatory over direct immunoassays (specificity 92% vs 78%) 1
• Calculate Free Androgen Index (FAI) if LC-MS/MS unavailable 1

Androgen Assessment (Second-Line)

• If testosterone normal but clinical suspicion high, measure androstenedione (75% sensitivity, 71% specificity) and DHEAS (75% sensitivity, 67% specificity) 1
• These have poorer specificity and serve only as adjunctive tests 1

Ovulation Assessment

• Measure mid-luteal progesterone (day 21 of 28-day cycle), with levels <6 nmol/L confirming anovulation 4, 1
• Measure LH and FSH between days 3-6 of cycle (average of three measurements 20 minutes apart) 4, 1
• LH/FSH ratio >2 suggests PCOS but is abnormal in only 35-44% of cases, making it a poor standalone marker 4, 1

Metabolic Screening (Mandatory for All PCOS Patients)

• Perform 2-hour oral glucose tolerance test with 75g glucose load regardless of BMI 1, 2
• Measure fasting lipid panel: total cholesterol, LDL, HDL, and triglycerides 1, 2
• Measure fasting glucose and insulin, with glucose/insulin ratio >4 suggesting insulin resistance 4, 1
• Calculate BMI (>25 indicates obesity) and waist-hip ratio (>0.9 indicates truncal obesity) 4, 1, 2

Imaging Assessment

Pelvic Ultrasound

• Perform transvaginal ultrasound with ≥8 MHz transducer as first-line imaging 1, 2
• Diagnostic criteria: ≥20 follicles per ovary (2-8 mm diameter) and/or ovarian volume ≥10 mL 4, 1
• Transvaginal approach is more sensitive than transabdominal for detecting structural abnormalities 4
• In adolescents, avoid ultrasound as first-line due to poor specificity and high false-positive rates 1
• Use transabdominal ultrasound in obese adolescents or when transvaginal is unacceptable 2

Critical Diagnostic Algorithm

1. Document clinical features: menstrual pattern (oligomenorrhea >35 days or amenorrhea >6 months), hirsutism (Ferriman-Gallwey score), acne, alopecia 4, 2

2. Exclude mimicking conditions first: TSH, prolactin, 17-OHP, and screen for Cushing's if clinically indicated 1, 2, 3

3. Confirm hyperandrogenism: Total and free testosterone by LC-MS/MS; if normal but suspicion high, add androstenedione and DHEAS 1

4. Confirm ovulatory dysfunction: Mid-luteal progesterone, LH/FSH ratio 4, 1

5. Perform pelvic ultrasound: Document follicle count and ovarian volume 1, 2

6. Complete metabolic screening: OGTT, fasting lipids, BMI, waist-hip ratio 1, 2

7. Apply Rotterdam criteria: Diagnosis requires 2 of 3 features (hyperandrogenism, ovulatory dysfunction, polycystic ovarian morphology) AFTER exclusion of other disorders 1, 2, 6

Important Caveats

• 30% of confirmed PCOS patients have normal testosterone levels, so diagnosis can be made with clinical hyperandrogenism alone plus irregular cycles 1
• Ultrasound should be performed days 3-9 of cycle for optimal assessment 4
• Avoid using AMH as standalone diagnostic test despite 92% sensitivity and 97% specificity, as it requires further validation and lacks assay standardization 1
• Pituitary MRI indicated if prolactin significantly elevated or galactorrhea present, though small lactotroph adenomas may escape detection 4
• Long-term surveillance required for endometrial cancer risk, especially with chronic anovulation, obesity, and hyperinsulinemia 2