Laboratory Tests to Confirm PCOS
Measure total testosterone (TT) and free testosterone (FT) using liquid chromatography-tandem mass spectrometry (LC-MS/MS) as your first-line laboratory tests for biochemical hyperandrogenism. 1, 2
First-Line Androgen Testing (Mandatory)
Order total testosterone (TT) and free testosterone (FT) measured by LC-MS/MS, which provides pooled sensitivity of 74% and specificity of 86% for TT, and superior sensitivity of 89% with specificity of 83% for FT. 1, 2
If LC-MS/MS is unavailable, calculate the Free Androgen Index (FAI) as an alternative, which shows sensitivity of 78% and specificity of 85%. 1, 2
Avoid direct immunoassays for testosterone measurement as they have significantly lower specificity (78%) compared to LC-MS/MS (92%), leading to false positives. 2
Second-Line Androgen Testing (If First-Line Normal)
If TT or FT are not elevated but clinical suspicion remains high, measure androstenedione (A4) with sensitivity of 75% and specificity of 71%. 1, 2
Measure DHEAS (dehydroepiandrosterone sulfate) if A4 is also considered, noting its sensitivity of 75% but poorer specificity of 67%. 1, 2
Recognize that A4 and DHEAS have inferior specificity compared to TT/FT and should only serve as adjunctive tests, not primary diagnostic markers. 2
Essential Tests to Exclude Mimicking Conditions
Measure thyroid-stimulating hormone (TSH) to rule out thyroid disease causing menstrual irregularity. 2, 3
Measure morning resting serum prolactin to exclude hyperprolactinemia. 2, 3
Measure 17-hydroxyprogesterone if DHEAS is elevated to rule out non-classical congenital adrenal hyperplasia. 4
Screen for Cushing's syndrome if patient presents with buffalo hump, moon facies, hypertension, abdominal striae, central fat distribution, easy bruising, or proximal myopathies. 2, 3
Consider androgen-secreting tumors if rapid onset of symptoms, severe hirsutism, or very high testosterone levels (typically >150-200 ng/dL). 2, 3
Metabolic Screening (Mandatory for All PCOS Patients)
Perform a two-hour oral glucose tolerance test with 75g glucose load to screen for glucose intolerance and type 2 diabetes, as women with PCOS have 31-35% prevalence of impaired glucose tolerance and 7.5-10% prevalence of type 2 diabetes. 2, 3, 5
Order fasting lipid panel including total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides, as PCOS women have lower HDL size and higher LDL particle numbers. 2, 3, 5
Calculate body mass index (BMI) and measure waist-hip ratio to assess for central obesity (WHR >0.9 indicates truncal obesity). 2, 3
Additional Hormonal Tests to Consider
Measure LH and FSH between days 3-6 of menstrual cycle, with an LH/FSH ratio >2 suggesting PCOS, though this is supportive rather than diagnostic. 2
Measure mid-luteal phase progesterone (day 21-23 of cycle) to confirm anovulation, with levels <6 nmol/L indicating anovulation. 2
Critical Pitfalls to Avoid
Do not use serum AMH levels as a single diagnostic test for PCOS, despite emerging evidence showing high sensitivity (92%) and specificity (97%) at threshold ≥35 pmol/L, as this is not yet guideline-recommended. 2, 3
Do not rely on ultrasound findings alone, as polycystic ovarian morphology may be present in up to one-third of healthy reproductive-aged women. 3
Repeat metabolic screening every 1-2 years based on family history of type 2 diabetes and BMI, and yearly in women with impaired glucose tolerance, as progression rates from normal glucose tolerance to impaired glucose tolerance and then to type 2 diabetes can be 5-15% within 3 years. 5
Remember that the diagnostic accuracy of testosterone varies by PCOS diagnostic criteria used—Rotterdam criteria show higher sensitivity (77%) but lower specificity (83%) compared to NIH criteria (sensitivity 51%, specificity 94%). 2