What laboratory tests confirm Polycystic Ovary Syndrome (PCOS)?

Laboratory Tests for Confirming 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 Tests

PCOS diagnosis requires laboratory confirmation of biochemical hyperandrogenism as part of the Rotterdam criteria, which states that at least two of three criteria must be present: chronic anovulation, hyperandrogenism (clinical or biochemical), and polycystic ovaries.

The following tests have the highest diagnostic accuracy:

• 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
  • Preferably measured by mass spectrometry for accuracy 1

• Free Androgen Index (FAI):

  • Sensitivity: 78%
  • Specificity: 85% 1
  • Alternative when mass spectrometry is unavailable
  • Cutoff value of 4.97 provides 71.4% sensitivity and 85.2% specificity 3

• Calculated Bioavailable Testosterone:

  • Sensitivity: 76%
  • Specificity: 83% 4
  • Cutoff of 0.78 nmol/L provides 75.9% sensitivity and 83.3% specificity 3

Secondary Androgen Tests

• Androstenedione (A4):

  • Sensitivity: 75%
  • Specificity: 71% 1
  • Abnormal in 53% of PCOS cases 2

• Dehydroepiandrosterone sulfate (DHEAS):

  • Sensitivity: 75%
  • Specificity: 67% 1
  • Less accurate than other androgen markers 4

Exclusionary Tests

These tests are essential to rule out other conditions that can mimic PCOS:

• Thyroid-Stimulating Hormone (TSH): To exclude 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 when clinically suspected 1

Metabolic Assessment

These tests are recommended, especially for patients with BMI >25 kg/m²:

• Fasting lipid profile: Total cholesterol, LDL, HDL, triglycerides 1
• Fasting glucose/insulin ratio: >4 suggests normal insulin sensitivity 1
• 2-hour 75g oral glucose tolerance test (OGTT): To assess insulin resistance and glucose intolerance 1

Hormonal Ratios and Patterns

• LH/FSH ratio: While traditionally used, this has lower sensitivity (55% for ratio >2:1) 5
• The combination of testosterone, androstenedione, and LH measurements has been shown to identify 86% of PCOS cases 2

Important Clinical Considerations

• Laboratory values should be interpreted in the context of clinical features (oligomenorrhea/amenorrhea, hirsutism, acne) and ultrasound findings 1, 6
• Hormone measurements should ideally be taken during the early follicular phase of the menstrual cycle in women who are menstruating 2
• Ultrasound findings alone are not sufficient for diagnosis and must be correlated with clinical and biochemical findings 1
• The diagnostic threshold for polycystic ovaries on ultrasound is ≥20 follicles (2-9mm) per ovary or ovarian volume ≥10ml 1

Common Pitfalls to Avoid

• Relying solely on LH/FSH ratio for diagnosis (low sensitivity) 2
• Using total testosterone alone without other androgen measurements
• Failing to exclude other endocrine disorders that can cause similar symptoms
• Not considering the assay method when interpreting results (mass spectrometry is preferred) 1
• Not accounting for SHBG levels, which can be affected by obesity and insulin resistance 2

The most recent evidence suggests that calculated testosterone indices (bioavailable testosterone, FAI, free testosterone) provide the best discrimination between PCOS patients and healthy controls 3, with free testosterone and FAI showing the highest diagnostic accuracy 4, 1.