What laboratory tests are recommended for the diagnosis and management of Polycystic Ovary Syndrome (PCOS)?

Laboratory Testing for PCOS Diagnosis

Measure total testosterone or free testosterone using liquid chromatography-tandem mass spectrometry (LC-MS/MS) as your first-line laboratory test, combined with TSH, prolactin, a 2-hour oral glucose tolerance test, and fasting lipid panel. 1, 2

Core Diagnostic Laboratory Tests

First-Line Androgen Assessment

• Total testosterone (TT) or free testosterone (FT) using LC-MS/MS is mandatory as the primary androgen marker, showing pooled sensitivity of 74% and specificity of 86% for TT, and superior sensitivity of 89% with specificity of 83% for FT 1
• LC-MS/MS demonstrates superior specificity (92%) compared to direct immunoassays (78%), which have higher false-positive rates and should be avoided 1
• Calculate Free Androgen Index (FAI) if LC-MS/MS is unavailable, though this is a less optimal alternative 1
• Important caveat: Total testosterone is abnormal in only 70% of women with confirmed PCOS, meaning 30% have normal testosterone levels despite having the condition 1

Essential Exclusionary Tests

• TSH to rule out thyroid disease as a cause of menstrual irregularity 1, 2
• Morning resting serum prolactin to exclude hyperprolactinemia (levels >20 μg/L considered abnormal) 1, 2
• 17-hydroxyprogesterone to exclude nonclassic congenital adrenal hyperplasia 2

Mandatory Metabolic Screening

• 2-hour oral glucose tolerance test with 75g glucose load to screen for glucose intolerance and type 2 diabetes, regardless of BMI 1, 2
• Fasting lipid panel including total cholesterol, LDL, HDL, and triglycerides 1, 2
• BMI calculation to assess obesity 1, 2
• Waist-hip ratio to identify central obesity (WHR >0.9 indicates truncal obesity) 1

Second-Line Tests When Clinical Suspicion Remains High

Additional Androgen Testing

• Androstenedione (A4) if TT/FT are normal but clinical suspicion persists, showing sensitivity of 75% and specificity of 71% 1
• DHEAS as an adjunctive test with sensitivity of 75% and specificity of 67%, particularly to rule out adrenal causes 1
• These have poorer specificity than TT/FT and should only be used as adjunctive tests, not first-line 1

Ovulation Assessment

• Mid-luteal phase progesterone to confirm anovulation, with levels <6 nmol/L indicating anovulation 1
• LH and FSH measured between days 3-6 of menstrual cycle, with LH/FSH ratio >2 suggesting PCOS 1
• Critical pitfall: LH/FSH ratio >2 is abnormal in only 35-44% of women with PCOS, making it a poor standalone diagnostic marker that should not be relied upon 1, 3

Insulin Resistance Markers

• Fasting glucose and insulin levels with glucose/insulin ratio >4 suggesting reduced insulin sensitivity 1

Tests to Exclude Mimicking Conditions

When to Screen for Specific Conditions

• Cushing's syndrome screening if patient has buffalo hump, moon facies, hypertension, abdominal striae, central fat distribution, easy bruising, or proximal myopathies 1, 2
• Androgen-secreting tumor evaluation if rapid onset of symptoms, severe hirsutism, or very high testosterone levels (androstenedione >10.0 nmol/L suggests adrenal/ovarian tumor) 1, 2
• Elevated DHEAS warrants consideration of congenital adrenal hyperplasia 1

Tests NOT Recommended as Standalone Diagnostics

Anti-Müllerian Hormone (AMH)

• AMH ≥35 pmol/L (5 ng/mL) shows high sensitivity (92%) and specificity (97%), but should not be used as an alternative to ultrasound or as a standalone diagnostic test due to lack of assay standardization 1
• AMH is a potential future surrogate marker but requires additional validation in different populations 1

Critical Clinical Context

PCOS can be diagnosed based solely on clinical hyperandrogenism (hirsutism, acne, or alopecia) plus irregular menstrual cycles without any abnormal laboratory values, per Rotterdam criteria requiring only two of three features 1. When clinical features and ultrasound findings are present, the absence of biochemical hyperandrogenism does not exclude PCOS 1.