Blood Work Evaluation for PCOS
Measure total testosterone (TT) and free testosterone (FT) using liquid chromatography-tandem mass spectrometry (LC-MS/MS) as your first-line laboratory tests for diagnosing biochemical hyperandrogenism in PCOS. 1, 2
First-Line Androgen Testing
The 2025 International PCOS Guidelines explicitly prioritize specific androgen measurements based on diagnostic accuracy:
- Total testosterone (TT) demonstrates pooled sensitivity of 74% and specificity of 86% for PCOS diagnosis 1, 2
- Free testosterone (FT) shows superior sensitivity of 89% with specificity of 83% 2
- LC-MS/MS is mandatory as the preferred assay method, showing superior specificity (92%) compared to direct immunoassays (78%) 1, 2
- Calculated free testosterone (cFT) should be assessed by equilibrium dialysis, ammonium sulfate precipitation, or calculated using Free Androgen Index (FAI) 1, 2
Important caveat: Total testosterone is abnormal in only 70% of women with confirmed PCOS, meaning 30% have normal testosterone levels despite having the condition 2. This underscores why clinical diagnosis doesn't require abnormal labs.
Second-Line Androgen Testing
If TT or FT are not elevated but clinical suspicion remains high:
- Androstenedione (A4) can be measured, with sensitivity of 75% and specificity of 71% 1, 2
- DHEAS can be measured, with sensitivity of 75% and specificity of 67% 1, 2
- Note the limitation: A4 and DHEAS have poorer specificity than TT/FT and should only be used as adjunctive tests 2
Essential Exclusionary Testing
To rule out other causes of hyperandrogenism and menstrual irregularity:
- Thyroid-stimulating hormone (TSH) to exclude thyroid disease as a cause of menstrual irregularity 2, 3
- Prolactin level using morning resting serum levels to exclude hyperprolactinemia (levels >20 μg/L considered abnormal) 2, 3
- 17-hydroxyprogesterone if elevated DHEAS levels suggest non-classical congenital adrenal hyperplasia 2, 4
Mandatory Metabolic Screening
All women with PCOS require metabolic evaluation due to increased cardiovascular and diabetes risk:
- Two-hour oral glucose tolerance test with 75g glucose load to screen for glucose intolerance and type 2 diabetes 2, 3
- Fasting lipid panel including total cholesterol, LDL, HDL, and triglycerides 2, 3
- Fasting glucose and insulin levels with glucose/insulin ratio >4 suggesting reduced insulin sensitivity 2
Additional Hormonal Tests (Lower Priority)
These tests have limited diagnostic value but may be considered in specific contexts:
- LH and FSH measured between days 3-6 of menstrual cycle, with LH/FSH ratio >2 suggesting PCOS, though this is abnormal in only 35-44% of women with PCOS, making it a poor standalone diagnostic marker 2, 5
- Progesterone in mid-luteal phase to confirm anovulation, with levels <6 nmol/L indicating anovulation 2
- Sex hormone-binding globulin (SHBG) for calculating free androgen index, though this doesn't significantly improve diagnostic accuracy beyond total testosterone alone 5
Emerging Biomarkers (Not Yet Standard)
- Anti-Müllerian Hormone (AMH) ≥35 pmol/L shows 92% sensitivity and 97% specificity, but should not replace ultrasound or serve as a standalone diagnostic test due to lack of assay standardization 2, 6
Critical Clinical Pitfalls
Avoid these common mistakes:
- Don't rely on LH/FSH ratio as a primary diagnostic criterion—it has poor sensitivity (abnormal in only 35-44% of PCOS cases) 2, 5
- Don't use direct immunoassays for testosterone measurement—they have significantly lower specificity (78%) compared to LC-MS/MS (92%) 1, 2
- Don't assume normal testosterone excludes PCOS—30% of women with confirmed PCOS have normal testosterone levels 2
- Don't use ultrasound findings alone for diagnosis—polycystic ovarian morphology may be present in up to one-third of normal reproductive-aged women 3
- Don't use AMH as a single diagnostic test—it requires further validation despite promising accuracy 2, 6