What blood work is recommended for the diagnosis and management of Polycystic Ovary Syndrome (PCOS)?

Blood Work for PCOS

For diagnosing and managing PCOS, obtain the following core laboratory tests: total or free testosterone (preferably by LC-MS/MS), TSH, prolactin, 2-hour 75g oral glucose tolerance test, and fasting lipid panel. 1, 2

Essential Diagnostic Laboratory Tests

Androgen Assessment

• Measure total testosterone or free testosterone as your first-line androgen test, using liquid chromatography-tandem mass spectrometry (LC-MS/MS) when available, which demonstrates 92% specificity compared to only 78% with direct immunoassays 2
• Total testosterone shows 74% sensitivity and 86% specificity for PCOS diagnosis, while free testosterone performs even better with 89% sensitivity and 83% specificity 2
• If testosterone levels are normal but clinical suspicion remains high, add androstenedione (75% sensitivity, 71% specificity) and DHEAS (75% sensitivity, 67% specificity) as second-line tests 2
• Important caveat: 30% of women with confirmed PCOS have normal testosterone levels, so normal results do not exclude the diagnosis when clinical features are present 2

Exclusion of Other Endocrine Disorders

• Measure TSH to rule out thyroid disease as a cause of menstrual irregularity 3, 1, 2
• Measure prolactin levels (preferably morning resting serum sample) to exclude hyperprolactinemia 3, 1, 2
• Measure 17-hydroxyprogesterone to exclude congenital adrenal hyperplasia 1

Metabolic Screening (Required for All PCOS Patients)

Glucose Metabolism

• Perform a 2-hour oral glucose tolerance test with 75g glucose load to screen for type 2 diabetes and glucose intolerance, regardless of BMI 3, 1, 2
• This is mandatory because women with PCOS have demonstrated increased risk for glucose intolerance and type 2 diabetes, and insulin resistance occurs independently of body weight 3, 1

Lipid Assessment

• Obtain fasting lipid panel including total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides 3, 2
• Women with PCOS frequently have dyslipidemia with disproportionately elevated LDL cholesterol and triglyceride levels 3

Additional Tests When Specific Features Present

When Cushing's Syndrome Suspected

• Order dexamethasone suppression test if patient has buffalo hump, moon facies, hypertension, abdominal striae, centripetal fat distribution, easy bruising, or proximal myopathies 3, 1, 2

When Ovarian or Adrenal Tumor Suspected

• Consider measuring androstenedione (levels >10.0 nmol/L suggest tumor) if there is rapid onset of symptoms, severe hirsutism, or very high testosterone levels 3, 2

Optional Adjunctive Tests

Ovulatory Function Assessment

• Measure LH and FSH between cycle days 3-6, with LH/FSH ratio >2 suggesting PCOS, though this is abnormal in only 35-44% of PCOS cases and is therefore a poor diagnostic marker 2
• Measure mid-luteal phase progesterone (levels <6 nmol/L indicate anovulation) 2

Anti-Müllerian Hormone (AMH)

• Do not use AMH as a single diagnostic test or as an alternative to ultrasound for detecting polycystic ovarian morphology 1
• While AMH ≥35 pmol/L (5 ng/mL) shows 92% sensitivity and 97% specificity, it requires further validation and is not currently recommended as a standalone diagnostic tool 1, 2

Critical Clinical Pitfalls

Remember that PCOS can be diagnosed with completely normal laboratory values if clinical hyperandrogenism (hirsutism, acne, alopecia) and irregular menstrual cycles are present, as the Rotterdam criteria require only two of three features 2. The physical examination findings of acanthosis nigricans (neck, axillae, under breasts, vulva) indicating insulin resistance, along with assessment of BMI and waist-to-hip ratio for central obesity, are essential components that laboratory tests alone cannot replace 3, 1.