Laboratory Evaluation for Suspected Polycystic Ovary Syndrome
Order total testosterone (or free/unbound testosterone), FSH, and assess ovulatory status as the core diagnostic laboratory tests for suspected PCOS, using the Rotterdam criteria which requires two of three features: androgen excess, ovulatory dysfunction, or polycystic ovaries. 1
Essential Initial Laboratory Tests
Androgen Assessment
- Measure total testosterone as the primary marker of biochemical hyperandrogenism 1, 2
- Free or unbound testosterone levels provide additional diagnostic value, particularly in ovulatory women with suspected PCOS who may have lower but still elevated androgen levels 3
- These tests establish biochemical hyperandrogenism, one of the three Rotterdam criteria 1
Ovulatory Function Assessment
- Obtain timed serum progesterone measurements (mid-luteal phase, typically day 21 of a 28-day cycle) to document ovulatory status 3
- This determines whether ovulatory dysfunction is present, the second Rotterdam criterion 1
- Note that approximately 74% of hyperandrogenic women may have PCOS even with reported normal menses, making this assessment critical 3
Gonadotropin Levels
- Measure FSH and LH to evaluate the hormonal profile characteristic of PCOS 3
- Elevated LH or an elevated LH:FSH ratio supports the diagnosis, though this is not required by Rotterdam criteria 1
Exclusion of Alternative Diagnoses
Mandatory Screening Tests
- 17-hydroxyprogesterone (17-OHP) to exclude non-classic congenital adrenal hyperplasia, a key androgen-excess disorder that mimics PCOS 1, 3
- TSH (thyroid-stimulating hormone) to exclude thyroid disorders that can cause menstrual irregularities 1
- Prolactin to rule out hyperprolactinemia as a cause of ovulatory dysfunction 1
Metabolic and Cardiovascular Risk Assessment
Glucose Metabolism
- Fasting glucose and/or oral glucose tolerance test (OGTT) to screen for diabetes and impaired glucose tolerance 1
- Fasting insulin levels to assess for insulin resistance, though this is not required for diagnosis 3
- These tests are critical because PCOS carries significant metabolic risk 1, 2
Lipid Profile
- Fasting lipid panel (total cholesterol, LDL, HDL, triglycerides) to evaluate cardiovascular risk factors 1
- Women with PCOS have increased cardiovascular disease risk requiring proactive screening 4
Additional Considerations Based on Clinical Context
When Indicated
- Hemoglobin A1c as an alternative or adjunct to glucose testing for diabetes screening 1
- Liver function tests (AST, ALT) if non-alcoholic fatty liver disease is suspected, particularly in adolescents with type 2 diabetes and PCOS 5
- Adrenocortical antibodies and additional thyroid antibodies only if autoimmune disorders are clinically suspected 6
Special Populations
- In adolescents, hyperandrogenism must be central to the presentation, as irregular menses alone is common in this age group 1
- Laboratory evaluation should be deferred until at least 2 years post-menarche when possible 1
- In adolescents with type 2 diabetes, evaluate for PCOS including laboratory studies when indicated 5
Important Clinical Caveats
- Timing matters: Obtain androgen levels in the early follicular phase (days 3-5) when possible for consistency 1
- Exclude pregnancy before initiating any evaluation for menstrual irregularity 1
- The diagnosis requires exclusion of other causes of hyperandrogenism and ovulatory dysfunction; laboratory testing serves both to establish PCOS features and rule out mimics 1
- Approximately 20-22% of women have polycystic ovarian morphology on ultrasound without meeting full PCOS criteria, so laboratory confirmation of hyperandrogenism or ovulatory dysfunction is essential 7
- Do not rely solely on ultrasound findings in adolescents, as polycystic ovarian morphology is common and non-specific in this age group 1