What lab tests are recommended for a patient with Polycystic Ovary Syndrome (PCOS)?

Laboratory Testing for PCOS

Measure total testosterone or free testosterone using liquid chromatography-tandem mass spectrometry (LC-MS/MS) as the first-line androgen test, along with TSH, prolactin, a 2-hour oral glucose tolerance test, and fasting lipid profile to diagnose PCOS and assess metabolic complications. 1

First-Line Core Laboratory Panel

Androgen Assessment

• Total testosterone (TT) or free testosterone (FT) measured by LC-MS/MS is mandatory as the primary diagnostic test, showing pooled sensitivity of 74% and specificity of 86% for TT, and superior sensitivity of 89% with specificity of 83% for FT 2, 1
• LC-MS/MS is the required assay method because it demonstrates superior specificity (92%) compared to direct immunoassays (78%), which have unacceptably high false-positive rates 2, 1
• If LC-MS/MS is unavailable, calculate Free Androgen Index (FAI) as an alternative, which shows sensitivity of 78% and specificity of 85% 1
• Calculated free testosterone (cFT) can be assessed by equilibrium dialysis or calculated using FAI, demonstrating pooled sensitivity of 89% and specificity of 83% 2, 1

Exclusion of Other Endocrine Disorders

• Measure thyroid-stimulating hormone (TSH) to rule out thyroid disease as a cause of menstrual irregularity 1
• Measure prolactin using morning resting serum levels to exclude hyperprolactinemia 1

Metabolic Screening (Essential Given High Cardiometabolic Risk)

• Perform a 2-hour oral glucose tolerance test with 75g glucose load to screen for glucose intolerance and type 2 diabetes 1
• Obtain fasting lipid panel including total cholesterol, LDL, HDL, and triglycerides 1
• Calculate body mass index (BMI) to assess obesity 1

Second-Line Androgen Testing (Only If Clinical Suspicion Remains High Despite Normal TT/FT)

• Measure androstenedione (A4) if testosterone levels are normal but clinical suspicion persists, showing sensitivity of 75% and specificity of 71% 2, 1
• Measure DHEAS to help rule out non-classical congenital adrenal hyperplasia, with sensitivity of 75% and specificity of 67% 2, 1
• These tests have poorer specificity than TT/FT and should only serve as adjunctive tests, not primary diagnostic markers 1

Additional Hormonal Assessment for Ovulatory Function

• Measure LH and FSH between days 3-6 of menstrual cycle, with an LH/FSH ratio >2 suggesting PCOS 1
• Measure mid-luteal phase progesterone to confirm anovulation, with levels <6 nmol/L indicating anovulation 1

Metabolic Risk Stratification

• Measure fasting glucose/insulin ratio using morning levels, with a ratio >4 suggesting reduced insulin sensitivity 1
• Measure waist-hip ratio to identify central obesity, with WHR >0.9 indicating truncal obesity 1
• Consider Anti-Müllerian Hormone (AMH) measurement, with threshold ≥35 pmol/L (5 ng/mL) showing high sensitivity (92%) and specificity (97%) for PCOS diagnosis 1

Red Flag Laboratory Evaluations (To Exclude Serious Mimics)

• Screen for Cushing's syndrome if patient presents with buffalo hump, moon facies, hypertension, abdominal striae, central fat distribution, easy bruising, or proximal myopathies 1
• Consider androgen-secreting tumors if rapid symptom onset, severe hirsutism, or very high testosterone levels (typically >10.0 nmol/L for androstenedione suggests adrenal/ovarian tumor) 1
• Evaluate for congenital adrenal hyperplasia if DHEAS levels are markedly elevated 1
• Check FSH levels to exclude primary ovarian failure 1

Critical Diagnostic Accuracy Considerations

The diagnostic accuracy of testosterone varies significantly by PCOS diagnostic criteria used: Rotterdam criteria show higher sensitivity (77%) but lower specificity (83%), while NIH criteria show lower sensitivity (51%) but higher specificity (94%) 2. This means you will detect more cases using Rotterdam criteria but with more false positives, so clinical context matters when interpreting borderline results.

Common pitfall: Direct immunoassays for testosterone have 78% specificity compared to 92% for LC-MS/MS 2. Using direct immunoassays will result in approximately 1 in 5 false-positive results, leading to overdiagnosis. Always insist on LC-MS/MS when available, or use calculated FAI as the next best alternative.