What laboratory tests should be ordered to evaluate a reproductive‑age woman with suspected polycystic ovary syndrome?

Laboratory Testing for Suspected PCOS

Order total testosterone 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 laboratory workup for suspected PCOS. 1, 2

First-Line Hormonal Tests

Androgen Assessment

• Measure total testosterone (TT) or free testosterone (FT) using liquid chromatography-tandem mass spectrometry (LC-MS/MS) as your primary androgen test, 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 LC-MS/MS is unavailable, calculate Free Androgen Index (FAI) as an alternative 1
• Important caveat: Total testosterone is abnormal in only 70% of women with confirmed PCOS, meaning 30% have normal testosterone levels despite having the condition 1

Exclusion of Other Endocrine Disorders

• Measure TSH to rule out thyroid disease as a cause of menstrual irregularity 1, 2, 3
• Measure morning fasting prolactin to exclude hyperprolactinemia, with levels >20 μg/L considered abnormal 1, 2
• If prolactin is elevated, confirm with 2-3 repeat samples taken 20-60 minutes apart via indwelling cannula to exclude stress-related spurious elevation 1, 2

Mandatory Metabolic Screening

Glucose Metabolism

• Perform a 2-hour 75g oral glucose tolerance test in all women with suspected PCOS, regardless of BMI or body weight, to detect type 2 diabetes and glucose intolerance 1, 2, 3
• This is critical because metabolic syndrome is twice as common in PCOS patients, and they are four times more likely to develop type 2 diabetes 4

Lipid Assessment

• Order a fasting lipid panel including total cholesterol, LDL, HDL, and triglycerides to assess cardiovascular risk 1, 2, 3
• Target values: LDL <100 mg/dL, HDL >35 mg/dL, triglycerides <150 mg/dL 1

Anthropometric Measurements

• Calculate BMI and waist-to-hip ratio to assess central obesity, with WHR >0.9 indicating truncal obesity 1, 2, 3
• Look for acanthosis nigricans on physical examination (neck, axillae, under breasts, vulva) indicating insulin resistance 2, 3

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

• If TT or FT are normal but clinical suspicion persists, measure androstenedione (A4) with 75% sensitivity and 71% specificity, and DHEAS with 75% sensitivity and 67% specificity 1
• These have poorer specificity than TT/FT and should only be used as adjunctive tests 1
• Androstenedione >10.0 nmol/L suggests adrenal/ovarian tumor 1

Additional Tests for Specific Clinical Scenarios

When to Screen for Other Conditions

• Measure 17-hydroxyprogesterone to exclude non-classical congenital adrenal hyperplasia, especially if DHEAS is elevated 1, 2
• Consider dexamethasone suppression test if 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 rapid onset of symptoms, severe hirsutism, or very high testosterone levels 1, 2

Optional Tests (Lower Diagnostic Yield)

• LH and FSH measured between cycle days 3-6 show an LH/FSH ratio >2 in only 35-44% of PCOS women, making this a poor standalone diagnostic marker 1, 5
• Mid-luteal progesterone (<6 nmol/L indicates anovulation) can confirm ovulatory dysfunction if needed 1
• Do NOT use AMH levels as an alternative for detecting polycystic ovarian morphology or as a single diagnostic test due to lack of standardization and no validated cut-offs 1, 2, 3

Critical Diagnostic Considerations

When Labs May Be Normal

• PCOS can be diagnosed with normal laboratory values if the patient has both clinical hyperandrogenism (hirsutism, acne, alopecia) AND irregular menstrual cycles, per Rotterdam criteria 1
• The diagnosis requires only two of three features: oligo/anovulation, clinical or biochemical hyperandrogenism, and polycystic ovarian morphology on ultrasound 1, 2

Common Pitfalls to Avoid

• Do not rely solely on LH/FSH ratio—it has poor sensitivity (35-44%) and should be abandoned as a primary diagnostic criterion 1, 5
• Ultrasound is NOT necessary for diagnosis if the patient already has irregular cycles AND hyperandrogenism, though it will identify the complete PCOS phenotype 1, 2
• In adolescents with gynecological age <8 years post-menarche, avoid using ultrasound for diagnosis due to high false-positive rates from physiologically normal multifollicular ovaries 1, 2, 3
• Screen ALL women with PCOS for metabolic dysfunction regardless of body weight, as insulin resistance occurs independently of BMI 2, 6

Long-Term Risk Assessment

• Women with PCOS have increased risk of endometrial cancer due to chronic anovulation, obesity, hyperinsulinemia, and reduced SHBG 2, 6
• Monitor cardiovascular risk factors every 6-12 months, including weight changes and blood pressure 1