Blood Work for Suspected PCOS
For suspected PCOS, order total testosterone (preferably by LC-MS/MS), TSH, prolactin, a 2-hour 75g oral glucose tolerance test, and a fasting lipid panel as your core diagnostic laboratory tests. 1
First-Line Androgen Testing
Total testosterone is your single best initial biochemical marker, showing 74% sensitivity and 86% specificity for PCOS diagnosis. 1 The method matters significantly—liquid chromatography-tandem mass spectrometry (LC-MS/MS) demonstrates superior specificity (92%) compared to direct immunoassays (78%), which can lead to false positives. 1
- Free testosterone has the highest diagnostic accuracy with 89% sensitivity and 83% specificity, and should be calculated using the Vermeulen equation from high-quality total testosterone and SHBG measurements rather than measured directly. 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 This is why clinical assessment remains paramount.
Essential Exclusionary Tests
You must rule out other causes of hyperandrogenism and menstrual irregularity:
- TSH to exclude thyroid disease as a cause of menstrual irregularity 1, 2
- Prolactin measured using morning resting serum levels to exclude hyperprolactinemia (levels >20 μg/L considered abnormal) 1
- If prolactin is elevated, confirm with 2-3 samples at 20-60 minute intervals via indwelling cannula to exclude stress-related spurious elevation 1
Mandatory Metabolic Screening
All women with PCOS require metabolic screening regardless of BMI, as insulin resistance occurs independently of body weight and affects both lean and overweight women. 2
- 2-hour oral glucose tolerance test with 75g glucose load to screen for glucose intolerance and type 2 diabetes 1, 2
- Fasting lipid panel including total cholesterol, LDL, HDL, and triglycerides (target LDL <100 mg/dL, HDL >35 mg/dL, triglycerides <150 mg/dL) 1
- Calculate BMI and waist-hip ratio to assess obesity and central fat distribution (WHR >0.9 indicates truncal obesity) 1, 2
Second-Line Androgen Tests (If Clinical Suspicion Remains High)
If total testosterone and free testosterone are normal but clinical suspicion persists:
- Androstenedione (A4) shows 75% sensitivity and 71% specificity 1
- DHEAS demonstrates 75% sensitivity and 67% specificity, particularly valuable in women <30 years to assess adrenal androgen production 1
- 17-hydroxyprogesterone to exclude non-classical congenital adrenal hyperplasia, especially if DHEAS is elevated 1, 2
Additional Hormonal Tests to Consider
- LH and FSH measured between days 3-6 of menstrual cycle, with LH/FSH ratio >2 suggesting PCOS 1
- Mid-luteal progesterone (levels <6 nmol/L indicate anovulation) to confirm anovulation 1
Tests NOT Recommended
- Do not use AMH levels as an alternative for detecting polycystic ovarian morphology or as a single test for PCOS diagnosis due to lack of standardization, no validated cut-offs, and significant overlap between women with and without PCOS 1, 2
- Avoid relying on LH/FSH ratio alone given its poor sensitivity (abnormal in only 35-44% of cases) 1, 3
Critical Clinical Pitfalls
If the patient is on hormonal contraception (including progestin-only implants like Implanon), hormone levels become unreliable for PCOS diagnosis. The contraception suppresses the hypothalamic-pituitary-ovarian axis, making LH/FSH ratios and testosterone measurements uninterpretable. Remove or allow the contraception to expire before testing. 1
Remember: 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, per Rotterdam criteria. 1 The absence of biochemical hyperandrogenism does not exclude PCOS when clinical features and ultrasound findings are present.