What laboratory tests should be obtained in a woman being evaluated for suspected polycystic ovary syndrome?

Laboratory Testing for Suspected PCOS

Order total testosterone or free testosterone (preferably by LC-MS/MS), TSH, prolactin, 2-hour oral glucose tolerance test with 75g glucose, and fasting lipid panel as your core diagnostic workup. 1, 2

First-Line Essential Laboratory Tests

Androgen Assessment

• Measure total testosterone (TT) and/or free testosterone (FT) using liquid chromatography-tandem mass spectrometry (LC-MS/MS) as your primary androgen markers, with TT showing 74% sensitivity and 86% specificity, while FT demonstrates superior sensitivity of 89% with 83% specificity 1
• LC-MS/MS is mandatory over direct immunoassays because it provides superior specificity (92% vs 78%), reducing false positives 1
• If TT or FT are normal but clinical suspicion remains high, add androstenedione (75% sensitivity, 71% specificity) and DHEAS (75% sensitivity, 67% specificity) as second-line tests 1
• Note that 30% of women with confirmed PCOS have normal testosterone levels, so normal results do not exclude the diagnosis 1

Exclusion of Other Endocrine Disorders

• Measure TSH to rule out thyroid disease as a cause of menstrual irregularity 1, 2
• Measure prolactin using morning resting serum levels to exclude hyperprolactinemia (levels >20 μg/L are abnormal); confirm any elevation with 2-3 samples at 20-60 minute intervals via indwelling cannula to exclude stress-related spurious elevation 1, 2
• Measure 17-hydroxyprogesterone to exclude congenital adrenal hyperplasia, particularly if DHEAS is elevated 2

Mandatory Metabolic Screening

Glucose Metabolism Assessment

• Order a 2-hour oral glucose tolerance test with 75g glucose load rather than hemoglobin A1c or fasting glucose alone, as this is the superior screening test for detecting impaired glucose tolerance in PCOS 1, 2, 3
• Screen all women with PCOS regardless of BMI or body weight, as insulin resistance occurs independently of weight and affects both lean and overweight women 2, 4

Lipid Assessment

• Order fasting lipid panel including total cholesterol, LDL, HDL, and triglycerides to assess dyslipidemia driven by insulin resistance 1, 2
• Target values: LDL <100 mg/dL, HDL >35 mg/dL, triglycerides <150 mg/dL 5, 1

Anthropometric Measurements

• Calculate BMI and measure waist-hip ratio to identify central obesity (WHR >0.9 indicates truncal obesity and exacerbates metabolic, reproductive, and psychological features) 1, 2
• Look for acanthosis nigricans on physical examination (neck, axillae, under breasts, vulva) indicating underlying insulin resistance 2

Optional Tests Based on Clinical Context

Ovulation Assessment

• Measure progesterone in mid-luteal phase to confirm anovulation (levels <6 nmol/L indicate anovulation) if fertility is a concern 1
• Measure LH and FSH between days 3-6 of menstrual cycle; an LH/FSH ratio >2 suggests PCOS, but this is abnormal in only 35-44% of women with PCOS, making it a poor standalone diagnostic marker 1

Exclusion of Rare Causes

• Consider dexamethasone suppression test if clinical features suggest Cushing's syndrome (buffalo hump, moon facies, hypertension, abdominal striae, central fat distribution, easy bruising, proximal myopathies) 1, 2
• Consider androgen-secreting tumor evaluation if rapid onset of symptoms, severe hirsutism, or very high testosterone levels 1

Tests NOT Recommended

• Do not use Anti-Müllerian Hormone (AMH) as a diagnostic test for PCOS, despite its high sensitivity (92%) and specificity (97%) at ≥35 pmol/L, due to lack of assay standardization, no validated cut-offs, and significant overlap between women with and without PCOS 1, 2
• Do not routinely order ultrasound if the patient already has both irregular menstrual cycles AND clinical/biochemical hyperandrogenism, as these two criteria are sufficient for diagnosis under Rotterdam criteria 1, 2

Critical Diagnostic Considerations

• PCOS can be diagnosed with completely normal laboratory values if clinical hyperandrogenism (hirsutism, acne, or alopecia) plus irregular menstrual cycles are present, as Rotterdam criteria require only two of three features 1, 6
• The diagnosis is one of exclusion after ruling out thyroid disease, hyperprolactinemia, congenital adrenal hyperplasia, and Cushing's syndrome 2, 6
• Clearly document the patient's phenotype when making the diagnosis, as there are four recognized phenotypes with different long-term health and metabolic implications 6