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

Initial Laboratory Tests for Suspected PCOS

Order total testosterone (preferably by LC-MS/MS), TSH, prolactin, a 2-hour 75-gram oral glucose tolerance test, and a fasting lipid panel as your core initial workup for suspected polycystic ovary syndrome. 1, 2

Core Diagnostic Laboratory Panel

Androgen Assessment

• Measure total testosterone using liquid chromatography-tandem mass spectrometry (LC-MS/MS) as your first-line androgen test, which demonstrates 74% sensitivity and 86% specificity for PCOS diagnosis 1, 3
• LC-MS/MS is mandatory over direct immunoassays because it shows superior specificity (92% versus 78%) and avoids false positives 1
• Calculate free testosterone using the Vermeulen equation from high-quality total testosterone and SHBG measurements if total testosterone is normal but clinical suspicion remains high—this achieves the highest sensitivity at 89% with 83% specificity 1
• If both total and free testosterone are normal but hyperandrogenism is strongly suspected clinically, measure androstenedione (75% sensitivity, 71% specificity) and DHEAS (75% sensitivity, 67% specificity) as second-line tests 1

Exclusion of Mimicking Endocrine Disorders

• Measure TSH to rule out thyroid disease as a cause of menstrual irregularity 1, 4, 3, 2
• Obtain morning fasting prolactin to exclude hyperprolactinemia; women with PCOS have a 3.15-fold increased risk of elevated prolactin 1, 4
• 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
• Measure 17-hydroxyprogesterone if DHEAS is elevated to exclude non-classical congenital adrenal hyperplasia 1, 3

Metabolic Screening (Mandatory Regardless of BMI)

• Perform a 2-hour oral glucose tolerance test with 75-gram glucose load to detect type 2 diabetes and impaired glucose tolerance—this is required for all women with suspected PCOS regardless of body weight because insulin resistance occurs independently of BMI 1, 4, 3, 2
• Order a fasting lipid panel including total cholesterol, LDL, HDL, and triglycerides to assess cardiovascular risk 1, 4, 3, 2
• Calculate BMI and measure waist-to-hip ratio; a ratio >0.9 indicates truncal obesity and exacerbates metabolic features 1, 4, 3

Additional Tests Based on Clinical Presentation

When to Measure LH and FSH

• Measure LH and FSH between cycle days 3-6 if you need to assess ovulatory function or rule out primary ovarian failure 1
• 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

When to Measure Progesterone

• Obtain mid-luteal phase progesterone (day 21 of a 28-day cycle) to confirm anovulation if fertility is a concern; levels <6 nmol/L indicate anovulation 1

Red Flags Requiring Immediate Additional Workup

• Screen for Cushing's syndrome with dexamethasone suppression test if the patient has buffalo hump, moon facies, hypertension, abdominal striae, central fat distribution, easy bruising, or proximal myopathies 1, 4, 3
• Consider androgen-secreting tumor if there is rapid onset of symptoms, severe hirsutism, very high testosterone levels (typically >150-200 ng/dL), or virilization (clitoromegaly, voice deepening) 1, 4, 2
• Measure androstenedione if levels >10.0 nmol/L, which suggests adrenal/ovarian tumor 1

Critical Diagnostic Considerations

What NOT to Order

• Do not use AMH levels as an alternative for detecting polycystic ovarian morphology or as a standalone diagnostic test—despite high sensitivity (92%) and specificity (97%) at thresholds ≥35 pmol/L, there is no assay standardization, no validated cut-offs, and significant overlap between women with and without PCOS 1, 4, 3

Physical Examination Essentials

• Look for clinical signs of hyperandrogenism: hirsutism (using Ferriman-Gallwey score), acne distribution, male-pattern alopecia, and clitoromegaly 4, 3
• Examine for acanthosis nigricans on the neck, axillae, under breasts, and vulva—this indicates underlying insulin resistance 3
• Document menstrual history; cycle length >35 days suggests chronic anovulation 4

Timing Considerations

• Do not perform hormone testing while the patient is on hormonal contraception (including progestin-only implants like Implanon), as these suppress the hypothalamic-pituitary-ovarian axis and make LH/FSH ratios and androgen levels unreliable 1
• Remove or allow contraceptive implants to expire before testing 1

Common Pitfalls to Avoid

• 30% of women with confirmed PCOS have normal testosterone levels, so do not exclude PCOS based solely on normal androgens if clinical features and menstrual irregularity are present 1
• Direct immunoassays for testosterone have lower specificity (78%) and may yield false positives—always request LC-MS/MS if available 1
• Remember that PCOS can be diagnosed with clinical hyperandrogenism plus irregular cycles alone, without any abnormal laboratory values, per Rotterdam criteria 1, 2
• All women with PCOS require metabolic screening regardless of weight; lean women with PCOS still have insulin resistance and increased cardiovascular risk 3, 5, 6