What lab work is recommended for a patient suspected of having Polycystic Ovary Syndrome (PCOS)?

Laboratory Workup for Suspected PCOS

For suspected PCOS, order total or free testosterone (preferably by LC-MS/MS), TSH, prolactin, a 2-hour 75g oral glucose tolerance test, and a fasting lipid panel as your core initial laboratory evaluation. 1, 2, 3

First-Line Hormonal Tests

Androgen Assessment

• Measure total testosterone (TT) or free testosterone (FT) as your primary androgen markers using liquid chromatography-tandem mass spectrometry (LC-MS/MS), which demonstrates superior specificity (92%) compared to direct immunoassays (78%). 1
• Total testosterone shows pooled sensitivity of 74% and specificity of 86%, while free testosterone demonstrates superior sensitivity of 89% with specificity of 83%. 1
• If LC-MS/MS is unavailable, calculate Free Androgen Index (FAI) using total testosterone and sex hormone-binding globulin (SHBG) as an alternative. 1

Exclusion of Other Endocrine Disorders

• Measure thyroid-stimulating hormone (TSH) to rule out thyroid disease as a cause of menstrual irregularity. 1, 2, 3
• Measure prolactin using morning resting serum levels to exclude hyperprolactinemia, with levels >20 μg/L considered abnormal. 1, 3

Mandatory Metabolic Screening

All women with suspected PCOS require metabolic screening regardless of body weight or BMI, as insulin resistance and metabolic dysfunction occur independently of obesity. 2, 4

Glucose Metabolism

• Perform a 2-hour oral glucose tolerance test with 75g glucose load—this is superior to hemoglobin A1C or fasting glucose alone for detecting impaired glucose tolerance in PCOS. 1, 2, 3
• Women with PCOS have substantially higher rates of insulin resistance, impaired glucose tolerance, and type 2 diabetes compared to women without the condition. 4, 5

Lipid Assessment

• Order a fasting lipid panel including total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides. 1, 2, 3

Anthropometric Measurements

• Calculate body mass index (BMI) and measure waist-hip ratio to identify central obesity, with WHR >0.9 indicating truncal obesity. 1, 2, 3

Second-Line Androgen Tests (If Clinical Suspicion Remains High)

• If total testosterone and free testosterone are normal but clinical suspicion persists, measure androstenedione (A4), which has sensitivity of 75% and specificity of 71%. 1
• Measure DHEAS (dehydroepiandrosterone sulfate) if A4 is also needed, with sensitivity of 75% and specificity of 67%—but recognize these have poorer specificity than TT/FT and should only serve as adjunctive tests. 1
• Measure 17-hydroxyprogesterone to exclude non-classical congenital adrenal hyperplasia, particularly if DHEAS is elevated. 1, 2

Additional Tests for Specific Clinical Scenarios

When Evaluating Ovulatory Function

• Measure luteinizing hormone (LH) and follicle-stimulating hormone (FSH) between days 3-6 of the menstrual cycle, with an LH/FSH ratio >2 suggesting PCOS—though this is abnormal in only 35-44% of women with PCOS, making it a poor standalone diagnostic marker. 1
• Measure progesterone in the mid-luteal phase to confirm anovulation, with levels <6 nmol/L indicating anovulation. 1

When Excluding Other Causes of Hyperandrogenism

• Consider dexamethasone suppression test if the patient has buffalo hump, moon facies, hypertension, abdominal striae, central fat distribution, easy bruising, or proximal myopathies to exclude Cushing's syndrome. 1, 2, 3
• Evaluate for androgen-secreting tumors if there is rapid onset of symptoms, severe hirsutism, or very high testosterone levels (testosterone >150-200 ng/dL warrants immediate evaluation). 1, 3, 6

Important Clinical Pitfalls

• Recognize that 30% of women with confirmed PCOS have normal testosterone levels, so the absence of biochemical hyperandrogenism does not exclude PCOS if clinical hyperandrogenism (hirsutism, acne, alopecia) and irregular cycles are present. 1
• Do not use serum Anti-Müllerian Hormone (AMH) as a single diagnostic test or as an alternative for detecting polycystic ovarian morphology, despite its high sensitivity (92%) and specificity (97%), as it requires further validation and assay standardization. 1, 2, 3
• Avoid using LH/FSH ratio as a primary diagnostic tool, as it is abnormal in only 35-44% of PCOS cases. 1
• Direct immunoassays for testosterone have significantly lower specificity (78%) compared to LC-MS/MS (92%), potentially leading to false positives—insist on LC-MS/MS when available. 1

Diagnostic Algorithm Summary

1. First step: Measure TT or FT using LC-MS/MS, TSH, and prolactin. 1, 3
2. Second step: If TT/FT normal but clinical suspicion high, measure A4 and DHEAS. 1
3. Concurrent metabolic screening: Order 2-hour OGTT and fasting lipid panel for all patients regardless of BMI. 1, 2, 3
4. Additional exclusion tests: Measure 17-hydroxyprogesterone if DHEAS elevated; consider dexamethasone suppression test if Cushing's features present. 1, 2