What blood tests are recommended for the diagnosis and management of Polycystic Ovary Syndrome (PCOS)?

Blood Tests for Diagnosis and Management of PCOS

The first-line laboratory tests for diagnosing PCOS should be total testosterone (TT) and free testosterone (FT) using mass spectrometry, as these provide the highest diagnostic accuracy for biochemical hyperandrogenism with sensitivities of 74% and 89%, and specificities of 86% and 83%, respectively. 1

Diagnostic Blood Tests for PCOS

Essential Androgen Tests

• Total Testosterone (TT): Sensitivity 74%, specificity 86% 1
• Free Testosterone (FT): Sensitivity 89%, specificity 83% 1
• Free Androgen Index (FAI): Alternative to FT when mass spectrometry is unavailable; sensitivity 78%, specificity 85% 1
• Androstenedione (A4): Sensitivity 75%, specificity 71% 1
• Dehydroepiandrosterone sulfate (DHEAS): Sensitivity 75%, specificity 67% 1

Exclusionary Tests (to rule out other conditions)

• Thyroid-Stimulating Hormone (TSH): To rule out thyroid disorders 1
• Prolactin: To exclude hyperprolactinemia 1
• 17-hydroxyprogesterone: To rule out late-onset congenital adrenal hyperplasia 1
• Overnight dexamethasone suppression test or 24-hour urinary free cortisol: To exclude Cushing's syndrome 1

Metabolic Assessment Tests

• Fasting lipid profile: Total cholesterol, LDL, HDL, triglycerides (especially for BMI >25 kg/m²) 1
• Fasting glucose/insulin ratio: >4 suggests normal insulin sensitivity 1
• 2-hour 75g oral glucose tolerance test (OGTT): For women with BMI >25 kg/m² to assess insulin resistance and glucose intolerance 1, 2

Clinical Application and Testing Algorithm

1. Initial Testing:

   • Start with Total Testosterone and Free Testosterone
   • Include TSH, Prolactin, and 17-hydroxyprogesterone to exclude other disorders

2. If BMI >25 kg/m²:

   • Add fasting glucose/insulin ratio
   • Perform 2-hour 75g OGTT
   • Assess lipid profile

3. If initial tests are borderline:

   • Add Androstenedione and DHEAS measurements
   • Consider Free Androgen Index if mass spectrometry is unavailable

Important Considerations

• Testosterone is the most frequently abnormal biochemical marker (70% of PCOS cases) 3
• The combination of testosterone, androstenedione, and LH measurements can identify up to 86% of PCOS cases 3
• The LH/FSH ratio, despite historical use, has low sensitivity and is no longer recommended as a primary diagnostic criterion 3
• Sex hormone binding globulin (SHBG) levels correlate negatively with BMI in PCOS patients 3

Pitfalls to Avoid

• Don't rely solely on LH/FSH ratio: This has poor sensitivity despite historical use 3
• Don't skip exclusionary tests: Conditions mimicking PCOS must be ruled out before confirming diagnosis 4
• Don't neglect metabolic testing: About 50-70% of PCOS patients have insulin resistance 2
• Don't interpret results in isolation: Laboratory findings must be correlated with clinical symptoms and ultrasound findings 1
• Don't use the same reference ranges for all assays: Each laboratory should establish its own reference ranges from regularly ovulating women in the early follicular phase 3

Remember that PCOS diagnosis requires at least two of three criteria: chronic anovulation, hyperandrogenism (clinical or biochemical), and polycystic ovaries, with exclusion of other relevant disorders 1. Laboratory testing is just one component of this diagnostic process.