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

Laboratory Tests Required for PCOS Diagnosis

Total testosterone (TT) and free testosterone (FT) are the absolutely necessary first-line laboratory tests for diagnosing PCOS, with additional tests required to exclude other causes of hyperandrogenism. 1

Essential Laboratory Tests for PCOS Diagnosis

First-Line Androgen Tests

• Total Testosterone (TT)

  • Sensitivity: 74%, Specificity: 86% 2
  • Preferably measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS) which offers superior specificity (92%) 2, 1

• Free Testosterone (FT)

  • Sensitivity: 89%, Specificity: 83% 2
  • Should be calculated rather than directly measured 1
  • Can be assessed by:
    • Equilibrium dialysis
    • Ammonium sulfate precipitation
    • Calculated using Free Androgen Index (FAI) 2

Tests to Exclude Other Causes of Hyperandrogenism

• Thyroid-stimulating hormone (TSH) 1
• Prolactin levels 1
• 17-hydroxyprogesterone (to rule out congenital adrenal hyperplasia) 1, 3
• Overnight dexamethasone suppression test or 24-hour urinary free cortisol (to exclude Cushing's syndrome) 1, 3

Additional Helpful Tests

Secondary Androgen Tests

If TT or FT are not elevated, consider:

• Free Androgen Index (FAI)

  • Sensitivity: 78%, Specificity: 85% 2
  • Calculated from total testosterone and SHBG 4
  • Cut-off value of approximately 4.97 (sensitivity 71.4%, specificity 85.2%) 5

• Androstenedione (A4)

  • Sensitivity: 75%, Specificity: 71% 2
  • Less specific than TT and FT 2

• Dehydroepiandrosterone sulfate (DHEAS)

  • Sensitivity: 75%, Specificity: 67% 2
  • Least specific of the androgen markers 2

Metabolic Evaluation

• Fasting lipid profile (total cholesterol, LDL, HDL, triglycerides) 1
• 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

Diagnostic Algorithm for PCOS

1. Start with first-line tests:

   • Total testosterone (TT) and free testosterone (FT)
   • TSH, Prolactin, 17-hydroxyprogesterone

2. If TT or FT elevated:

   • Proceed with transvaginal ultrasound (between days 3-9 of menstrual cycle)
   • Diagnostic threshold: ≥20 follicles (2-9mm) per ovary or ovarian volume ≥10ml 1

3. If TT and FT normal but strong clinical suspicion:

   • Test FAI, Androstenedione, and DHEAS 2

4. If hyperandrogenism confirmed:

   • Rule out other causes with dexamethasone suppression test or 24-hour urinary free cortisol

5. Complete metabolic evaluation:

   • Fasting lipid profile
   • Glucose tolerance test
   • Calculate BMI and waist-hip ratio 1

Important Considerations

• LC-MS/MS is the preferred method for testosterone measurement due to higher accuracy 2, 1
• Calculated testosterone indices (FAI, cFT) are more specific than measured androgen markers alone 4, 5
• Free testosterone reflects both ovarian and metabolic disturbances, making it particularly valuable 6
• The diagnosis requires at least two of three criteria: chronic anovulation, hyperandrogenism (clinical or biochemical), and polycystic ovaries 1

Common Pitfalls to Avoid

• Using automated immunoassays for testosterone measurement, which are often inaccurate in women 6
• Relying solely on LH/FSH ratio for diagnosis, which has poor sensitivity 7
• Failing to exclude other causes of hyperandrogenism 1, 3
• Misdiagnosing functional hypothalamic amenorrhea with polycystic ovarian morphology (FHA-PCOM) as PCOS 1

Remember that while laboratory tests are crucial, the diagnosis of PCOS requires a combination of clinical, biochemical, and ultrasound findings according to the Rotterdam criteria.