Blood Tests for PCOS Diagnosis and Management
Essential First-Line Laboratory Tests
Measure total testosterone or free testosterone using liquid chromatography-tandem mass spectrometry (LC-MS/MS) as the primary diagnostic test, which demonstrates 74% sensitivity and 86% specificity for total testosterone, and superior 89% sensitivity with 83% specificity for free testosterone. 1
Core Androgen Assessment
- Total testosterone (TT) is the single best biochemical marker, abnormal in 70% of women with PCOS, making it more reliable than any other hormonal test 1, 2
- Free testosterone (FT) shows even better diagnostic accuracy than total testosterone and should be measured alongside it 1
- LC-MS/MS is mandatory over direct immunoassays because it provides superior specificity (92% vs 78%), reducing false positives 3, 1
- If LC-MS/MS is unavailable, calculate Free Androgen Index (FAI) using total testosterone and sex hormone binding globulin (SHBG) 1
Exclusion of Other Endocrine Disorders
- Thyroid-stimulating hormone (TSH) must be measured to exclude thyroid disease as a cause of menstrual irregularity 3, 1, 4
- Prolactin should be measured using morning resting serum levels to exclude hyperprolactinemia, with levels >20 μg/L considered abnormal 3, 1, 4
- 17-hydroxyprogesterone is required to exclude nonclassic congenital adrenal hyperplasia 3, 4
Mandatory Metabolic Screening
All women with PCOS require metabolic screening regardless of BMI, as insulin resistance occurs independently of body weight. 3
Glucose Metabolism Assessment
- 2-hour oral glucose tolerance test (75g glucose load) is the gold standard for detecting type 2 diabetes and glucose intolerance, required for all PCOS patients regardless of BMI 3, 1, 4
- Fasting glucose and insulin levels with glucose/insulin ratio calculation (ratio >4 suggests reduced insulin sensitivity) 1
Lipid Profile
- Fasting lipid panel including total cholesterol, LDL, HDL, and triglycerides to assess cardiovascular risk 1, 4
Second-Line Androgen Tests (Only If First-Line Normal)
If total testosterone and free testosterone are normal but clinical suspicion remains high:
- Androstenedione (A4) has 75% sensitivity and 71% specificity, but poorer accuracy than testosterone 1
- DHEAS has 75% sensitivity and 67% specificity, useful for ruling out adrenal causes 1
- These should only be used as adjunctive tests, not primary diagnostic markers 1
Optional Tests with Limited Diagnostic Value
LH/FSH Ratio
- LH and FSH measured between cycle days 3-6, with LH/FSH ratio >2 suggesting PCOS 1
- Critical caveat: This ratio is abnormal in only 35-44% of women with PCOS, making it a poor standalone diagnostic marker that should not be used as a primary criterion 1, 2
- The LH/FSH ratio has been largely abandoned due to low sensitivity 2
Progesterone
- Mid-luteal phase progesterone (levels <6 nmol/L indicate anovulation) can confirm ovulatory dysfunction but is not required if menstrual irregularity is already documented 1
Tests NOT Recommended for Diagnosis
Anti-Müllerian hormone (AMH) should not be used as an alternative for detecting polycystic ovarian morphology or as a single test for PCOS diagnosis, despite showing 92% sensitivity and 97% specificity at ≥35 pmol/L, due to lack of assay standardization 3, 1
Critical Diagnostic Pitfall
30% of women with confirmed PCOS have normal testosterone levels, so the absence of biochemical hyperandrogenism does not exclude PCOS when clinical hyperandrogenism (hirsutism, acne, alopecia) and ovulatory dysfunction are present 1. The Rotterdam criteria require only two of three features: oligo/anovulation, clinical or biochemical hyperandrogenism, and polycystic ovarian morphology on ultrasound 3, 1.