What laboratory tests indicate Polycystic Ovary Syndrome (PCOS)?

Laboratory Tests for Diagnosing 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 in PCOS. 1

Primary Diagnostic Laboratory Tests

• Total Testosterone (TT)

  • Sensitivity: 74%, Specificity: 86% 1
  • Most frequently abnormal biochemical marker (70% of PCOS cases) 2

• Free Testosterone (FT)

  • Sensitivity: 89%, Specificity: 83% 1
  • Preferred method: Mass spectrometry
  • Alternative: Free Androgen Index (FAI) when mass spectrometry is unavailable
    • FAI Sensitivity: 78%, Specificity: 85% 1, 3

Secondary Laboratory Tests

If TT or FT are not elevated but clinical suspicion remains high:

• Androstenedione (A4)

  • Sensitivity: 75%, Specificity: 71% 1, 3

• Dehydroepiandrosterone Sulfate (DHEAS)

  • Sensitivity: 75%, Specificity: 67% 3
  • Note: Less specific than TT or FT 1

Tests to Exclude Other Causes of Hyperandrogenism

• Thyroid-Stimulating Hormone (TSH) - To rule out thyroid disorders 3, 4
• Prolactin - To exclude hyperprolactinemia 3, 4
• 17-hydroxyprogesterone - To rule out late-onset congenital adrenal hyperplasia 3, 4
• Dexamethasone suppression test or 24-hour urinary free cortisol - To exclude Cushing's syndrome 3

Metabolic Assessment

• Fasting lipid profile (total cholesterol, LDL, HDL, triglycerides) 3
• Fasting glucose/insulin ratio (>4 suggests normal insulin sensitivity) 5
• 2-hour 75g oral glucose tolerance test (OGTT) - Particularly for women with BMI >25 kg/m² 3
  • Best simple office-based method to assess both insulin resistance and glucose intolerance 5

Diagnostic Pitfalls to Avoid

1. Relying solely on LH/FSH ratio

   • Despite historical use, LH/FSH ratio has low sensitivity (present in only 41-44% of PCOS cases) 2
   • Should not be used as a primary diagnostic criterion 2

2. Failing to account for assay variability

   • Absolute gonadotropin values can differ significantly between assay methods 2
   • Laboratory-specific reference ranges should be used 2

3. Over-reliance on ultrasound findings alone

   • Ultrasound findings must be correlated with clinical and biochemical findings 3
   • Normal ovarian appearance on ultrasound does not exclude PCOS (31% of PCOS patients may have normal-appearing ovaries) 6

Diagnostic Algorithm

1. Start with TT and FT (or FAI if mass spectrometry unavailable)
2. If TT or FT elevated → supports PCOS diagnosis (when combined with clinical criteria)
3. If TT and FT normal but clinical suspicion high → measure A4 and DHEAS
4. Regardless of androgen results → perform exclusionary tests (TSH, prolactin, 17-hydroxyprogesterone)
5. For all patients, especially those with BMI >25 kg/m² → assess metabolic parameters (lipid profile, glucose tolerance)

Remember that laboratory tests are only part of the diagnostic criteria for PCOS, which requires at least two of three features: oligo/anovulation, clinical or biochemical hyperandrogenism, and polycystic ovaries on ultrasound, after exclusion of other disorders 3, 4.