What laboratory tests are required for the diagnosis of Polycystic Ovary Syndrome (PCOS)?

Laboratory Tests Required for PCOS Diagnosis

The diagnosis of Polycystic Ovary Syndrome (PCOS) requires specific laboratory tests to evaluate hormonal status, exclude other causes of hyperandrogenism, and assess metabolic parameters, including total testosterone, free testosterone, TSH, prolactin, and 17-hydroxyprogesterone. 1

Core Diagnostic Tests for PCOS

Hormonal Assessment

• Total testosterone (TT): Should be measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS) for superior specificity (92%) 1
• Free testosterone (FT): Should be calculated rather than directly measured, using methods such as:
  • Free Androgen Index (FAI) - sensitivity 78%, specificity 85%
  • Equilibrium dialysis
  • Ammonium sulfate precipitation 1
• Androstenedione (A4): Sensitivity 75%, specificity 71% 1
• Dehydroepiandrosterone sulfate (DHEAS): Sensitivity 75%, specificity 67% 1

Tests to Exclude Other Causes of Hyperandrogenism

• Thyroid-stimulating hormone (TSH) 1
• Prolactin levels 1
• 17-hydroxyprogesterone to rule out congenital adrenal hyperplasia 1
• Overnight dexamethasone suppression test or 24-hour urinary free cortisol test to rule out Cushing's syndrome 1

Metabolic Evaluation

• Fasting lipid profile: Total cholesterol, LDL, HDL, triglycerides 1
• Glucose metabolism assessment:
  • 2-hour 75g oral glucose tolerance test (particularly in women with BMI >25 kg/m²) 1
  • Fasting glucose/insulin ratio (>4 suggests normal insulin sensitivity) 1

Important Considerations

Timing of Tests

• Hormonal tests are best performed in the early follicular phase (days 3-5) of the menstrual cycle for women with regular cycles
• For women with irregular cycles, tests can be performed at any time, but interpretation should consider the cycle phase 2

Imaging Studies

• Transvaginal ultrasound should be performed between days 3-9 of the menstrual cycle 1
• Diagnostic threshold: ≥20 follicles (2-9mm) per ovary or ovarian volume ≥10ml 1
• Note that ultrasound findings alone are not sufficient for diagnosis and must be correlated with clinical and biochemical findings 3

Age-Specific Considerations

• In adolescents, AMH (Anti-Müllerian Hormone) testing is not currently recommended for diagnosis 3
• Ultrasound is not recommended for diagnosis until 8 years post-menarche 3
• In adolescents, diagnosis requires both hyperandrogenism and ovulatory dysfunction 3

Diagnostic Approach Algorithm

1. First-line laboratory tests:

   • Total testosterone (using LC-MS/MS)
   • Calculated free testosterone or FAI
   • TSH and prolactin

2. Second-line laboratory tests (if initial results are abnormal or clinical suspicion remains high):

   • 17-hydroxyprogesterone
   • Androstenedione
   • DHEAS
   • Dexamethasone suppression test or 24-hour urinary free cortisol (if Cushing's syndrome is suspected)

3. Metabolic assessment:

   • Fasting lipid profile
   • 2-hour 75g oral glucose tolerance test
   • Fasting glucose/insulin ratio

4. Imaging:

   • Transvaginal ultrasound (in adults) to assess follicle count and ovarian volume

Common Pitfalls to Avoid

• Relying solely on ultrasound findings for diagnosis 1
• Misdiagnosing functional hypothalamic amenorrhea with polycystic ovarian morphology (FHA-PCOM) as PCOS phenotype D 1
• Failing to exclude other causes of hyperandrogenism 2
• Not considering age-specific diagnostic criteria, especially in adolescents 3
• Using direct free testosterone assays, which are less reliable than calculated methods 1

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, 2.