Laboratory Testing for PCOS
Core Diagnostic Laboratory Tests
The essential laboratory workup for PCOS includes total or free testosterone (preferably by mass spectrometry), TSH, prolactin, 17-hydroxyprogesterone, a 2-hour oral glucose tolerance test with 75g glucose load, and a fasting lipid panel. 1, 2
First-Line Androgen Assessment
- Measure total testosterone (TT) and free testosterone (FT) using liquid chromatography-tandem mass spectrometry (LC-MS/MS) as the mandatory first-line tests, with TT showing 74% sensitivity and 86% specificity, while FT demonstrates superior sensitivity of 89% with 83% specificity 2
- LC-MS/MS is critical because direct immunoassays have significantly lower specificity (78%) compared to LC-MS/MS (92%), leading to false positives 2
- If LC-MS/MS is unavailable, calculate Free Androgen Index (FAI) using total testosterone and sex hormone-binding globulin 2
Exclusion of Alternative Diagnoses
- Measure TSH to exclude thyroid disease as a cause of menstrual irregularity, which can mimic PCOS 1, 2
- Measure morning resting serum prolactin to rule out hyperprolactinemia, with levels >20 μg/L considered abnormal 1, 2
- Measure 17-hydroxyprogesterone to exclude nonclassic congenital adrenal hyperplasia, particularly if DHEAS is elevated 1
Second-Line Androgen Testing (If Clinical Suspicion Remains High)
- If TT and FT are normal but clinical suspicion persists, measure androstenedione (A4) with 75% sensitivity and 71% specificity, and DHEAS with 75% sensitivity and 67% specificity 2
- These have poorer specificity than TT/FT and should only serve as adjunctive tests, not primary diagnostic markers 2
Mandatory Metabolic Screening
All PCOS patients require metabolic screening regardless of BMI due to increased risk of type 2 diabetes, dyslipidemia, and cardiovascular disease. 1, 2
- Perform a 2-hour oral glucose tolerance test with 75g glucose load to screen for type 2 diabetes and glucose intolerance in all PCOS patients 1, 2
- Order a fasting lipid panel including total cholesterol, LDL, HDL, and triglycerides to assess dyslipidemia driven by insulin resistance 1, 2
- Calculate BMI and measure waist-hip ratio to assess body habitus and metabolic risks, with WHR >0.9 indicating truncal obesity 1, 2
Optional Hormonal Tests for Specific Clinical Scenarios
- Measure LH and FSH between days 3-6 of menstrual cycle if assessing ovulatory function, though an LH/FSH ratio >2 is abnormal in only 35-44% of PCOS women, making it a poor standalone diagnostic marker 2
- Measure mid-luteal phase progesterone to confirm anovulation, with levels <6 nmol/L indicating anovulation 2
- Consider fasting glucose/insulin ratio, with a ratio >4 suggesting reduced insulin sensitivity 2
Emerging Biomarkers (Not Yet Recommended for Routine Use)
- Anti-Müllerian hormone (AMH) ≥35 pmol/L shows 92% sensitivity and 97% specificity, but should not be used as an alternative to ultrasound or as a standalone diagnostic test due to lack of assay standardization and need for validation across populations 2
Critical Diagnostic Caveat
A woman can be diagnosed with PCOS based solely on clinical hyperandrogenism (hirsutism, acne, or alopecia) plus irregular menstrual cycles without any abnormal laboratory values, as the Rotterdam criteria require only two of three features 2. Total testosterone is abnormal in only 70% of women with confirmed PCOS, meaning 30% have normal testosterone levels despite having the condition 2. Therefore, normal laboratory values do not exclude PCOS when clinical features and ultrasound findings are present 2.
Additional Screening Based on Clinical Presentation
- 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, 2
- Consider androgen-secreting tumors if there is rapid onset of symptoms, severe hirsutism, or very high testosterone levels (androstenedione >10.0 nmol/L) 1, 2