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

Laboratory Tests Needed for Diagnosis of PCOS

The first-line laboratory tests for diagnosing PCOS should be total testosterone (TT) and free testosterone (FT) using mass spectrometry methods, as these provide the highest diagnostic accuracy. 1

Primary Diagnostic Tests

Based on the most recent evidence, the following tests are recommended for diagnosing biochemical hyperandrogenism in PCOS:

• First-line androgen tests:
  • Total testosterone (TT): Sensitivity 74%, Specificity 86% 1
  • Free testosterone (FT): Sensitivity 89%, Specificity 83% 1
  • Free Androgen Index (FAI): Sensitivity 78%, Specificity 85% 2

When mass spectrometry methods are unavailable, FAI can be used as an alternative 1. Total testosterone is the most frequently abnormal marker, elevated in approximately 70% of PCOS cases (>2.5 nmol/L) 2.

Additional Recommended Tests

To complete the diagnostic workup and exclude other conditions, these additional tests should be performed:

• Thyroid-stimulating hormone (TSH) - to rule out thyroid dysfunction 2
• Prolactin - to exclude hyperprolactinemia 2
• 17-hydroxyprogesterone - to rule out congenital adrenal hyperplasia 2

If initial androgen tests are not elevated, consider:

• Androstenedione (A4): Sensitivity 75%, Specificity 71% 1, 2
• Dehydroepiandrosterone sulfate (DHEAS): Sensitivity 75%, Specificity 67% 1, 2

Diagnostic Approach

1. Measure TT and FT as first-line tests
2. Calculate FAI if mass spectrometry methods are unavailable
3. Consider A4 and DHEAS if TT or FT are not elevated (noting their poorer specificity)
4. Rule out other conditions with TSH, prolactin, and 17-hydroxyprogesterone

Important Considerations

• The LH/FSH ratio is often elevated (>2:1) in 55% of PCOS patients, but this has low sensitivity and should not be used as a primary diagnostic criterion 2, 3, 4
• Liquid chromatography with tandem mass spectrometry (LC-MS/MS) has superior sensitivity and specificity compared to direct immunoassay methods 1
• Free testosterone should be assessed by equilibrium dialysis techniques or calculated using FAI for greater accuracy 1, 5

Common Pitfalls to Avoid

• Relying solely on LH/FSH ratio - This has poor sensitivity (only abnormal in 41-44% of cases) 4
• Using only ultrasound findings - 31% of PCOS patients may have normal-appearing ovaries on ultrasound 3
• Not excluding other disorders - Conditions like hyperprolactinemia and congenital adrenal hyperplasia can mimic PCOS symptoms 5, 3
• Using inappropriate reference ranges - Hormone values should be compared to those from regularly ovulating women in the early follicular phase 4

Remember that PCOS diagnosis requires at least two of three criteria: chronic anovulation, hyperandrogenism (clinical or biochemical), and polycystic ovaries on ultrasound 2, 5. Laboratory testing is just one component of the diagnostic process, which should be integrated with clinical findings and imaging results.