Laboratory Tests for Diagnosing PCOS
For diagnosing Polycystic Ovary Syndrome (PCOS), you should obtain total testosterone, free testosterone, TSH, prolactin, 17-hydroxyprogesterone, a 2-hour oral glucose tolerance test with 75g glucose load, and a fasting lipid profile. 1
Core Laboratory Panel
The diagnosis of PCOS requires at least two of three criteria: chronic anovulation, hyperandrogenism (clinical or biochemical), and polycystic ovaries, with exclusion of other relevant disorders. To properly evaluate these criteria and rule out other conditions, the following tests are recommended:
Hormone Evaluation
Androgen Assessment
- Total testosterone (sensitivity 74%, specificity 86%)
- Free testosterone (sensitivity 89%, specificity 83%)
- Free Androgen Index (FAI) (sensitivity 78%, specificity 85%)
- Androstenedione (sensitivity 75%, specificity 71%)
- DHEAS (sensitivity 75%, specificity 67%)
Other Hormones
- Follicle-stimulating hormone (FSH)
- Luteinizing hormone (LH)
- Estradiol
- Prolactin
Exclusion of Other Disorders
- Thyroid-stimulating hormone (TSH)
- 17-hydroxyprogesterone (to rule out congenital adrenal hyperplasia)
- Overnight dexamethasone suppression test or 24-hour urinary free cortisol (if Cushing's syndrome is suspected)
Metabolic Assessment
Metabolic screening is crucial as PCOS patients have higher rates of insulin resistance and metabolic disorders:
- 2-hour oral glucose tolerance test with 75g glucose load (preferred over hemoglobin A1C or fasting glucose)
- Fasting lipid profile (total cholesterol, LDL, HDL, triglycerides)
Timing Considerations
- FSH, LH, and estradiol should be measured between days 3-6 of the menstrual cycle
- Progesterone should be measured during the mid-luteal phase (approximately day 21 of a 28-day cycle)
Diagnostic Imaging
While not a laboratory test, transvaginal ultrasound is recommended for diagnosing polycystic ovarian morphology, with a diagnostic threshold of ≥20 follicles (2-9mm) per ovary or ovarian volume ≥10ml. However, ultrasound should not be used for diagnosis in women <8 years after menarche due to high incidence of multi-follicular ovaries. 1
Common Pitfalls and Caveats
Underutilization of metabolic screening: Despite guidelines recommending comprehensive metabolic assessment, studies show that only 7% of physicians order the recommended 2-hour oral glucose tolerance test for PCOS patients. 2
Reliance on LH/FSH ratio: While historically used, the LH/FSH ratio has low sensitivity (41-44%) and should not be used as a primary diagnostic criterion. 3
Age and ethnicity considerations: Normal reference ranges for androgens may vary by age and ethnicity, which should be considered when interpreting laboratory results. 1
Timing of tests: Hormone levels fluctuate throughout the menstrual cycle, making the timing of blood draws crucial for accurate interpretation. 1
By following this comprehensive laboratory assessment, you can accurately diagnose PCOS while excluding other conditions that may present with similar symptoms, and identify metabolic abnormalities that require management.