What laboratory tests are recommended for the workup of polycystic ovary syndrome (PCOS)?

Laboratory Workup for Polycystic Ovary Syndrome (PCOS)

Order total testosterone by liquid chromatography-tandem mass spectrometry (LC-MS/MS), TSH, prolactin, a 2-hour oral glucose tolerance test with 75g glucose load, and a fasting lipid panel as your core laboratory evaluation for suspected PCOS. 1, 2

First-Line Hormonal Tests

Androgen Assessment

• Measure total testosterone using LC-MS/MS as the single best initial biochemical marker, demonstrating 74% sensitivity and 86% specificity for detecting hyperandrogenism. 1, 2
• LC-MS/MS assays provide superior specificity (92%) compared to direct immunoassays (78%), which have unacceptably high false-positive rates. 1, 2
• Calculate free testosterone using the Vermeulen equation from high-quality total testosterone and SHBG measurements, which yields the highest diagnostic performance at 89% sensitivity and 83% specificity. 1, 2
• The Free Androgen Index (FAI = [total testosterone/SHBG] × 100) can serve as an alternative when LC-MS/MS is unavailable, offering 78% sensitivity and 85% specificity, but use cautiously when SHBG <30 nmol/L. 1

Exclusion of Mimicking Conditions

• Measure TSH to exclude thyroid disease as a cause of menstrual irregularity. 1, 2
• Obtain a morning resting prolactin level to rule out hyperprolactinemia; women with PCOS have a 3.15-fold increased risk of elevated prolactin (>20 µg/L is abnormal). 1, 2
• If prolactin is elevated, confirm with 2-3 samples at 20-60 minute intervals via indwelling cannula to exclude stress-related spurious elevation. 2

Second-Line Androgen Tests (Only When Primary Tests Are Normal but Clinical Suspicion Remains High)

• Measure androstenedione if total/free testosterone are normal; it provides 75% sensitivity and 71% specificity, and values >10.0 nmol/L raise suspicion for adrenal or ovarian androgen-secreting tumor. 1, 2
• Measure DHEAS under the same conditions; it offers 75% sensitivity and 67% specificity and is most reliable for adrenal androgen production, particularly valuable in women <30 years. 1, 2
• Age-adjusted DHEAS thresholds (≥3800 ng/mL for ages 20-29, ≥2700 ng/mL for ages 30-39) should prompt evaluation for non-classical congenital adrenal hyperplasia. 2

Mandatory Metabolic Screening

Glucose Assessment

• Perform a 2-hour oral glucose tolerance test with 75g glucose load to screen for impaired glucose tolerance or type 2 diabetes; fasting glucose >7.8 mmol/L (>140 mg/dL) is diagnostic of diabetes. 1, 2
• All women with PCOS require metabolic screening regardless of BMI, because insulin resistance occurs independently of body weight. 1

Lipid Assessment

• Obtain a fasting lipid panel including total cholesterol, LDL, HDL, and triglycerides to assess cardiovascular risk. 1, 2
• Target values: LDL <100 mg/dL (<2.6 mmol/L), HDL >35 mg/dL (>0.91 mmol/L), and triglycerides <150 mg/dL (<1.7 mmol/L). 3

Anthropometric Measures

• Calculate BMI and measure waist-hip ratio; a WHR >0.9 indicates truncal obesity and heightened metabolic risk. 1, 2

Optional Tests Based on Clinical Context

Ovulatory Function Assessment

• Measure LH and FSH on cycle days 3-6 (if cycles occur), averaging three samples taken 20 minutes apart; an LH/FSH ratio >2 supports PCOS but is present in only 35-44% of affected women, making it a poor standalone diagnostic marker. 2, 4
• Measure mid-luteal phase progesterone (day 21 of a 28-day cycle); levels <6 nmol/L confirm anovulation. 2

Anti-Müllerian Hormone (AMH)

• Do NOT use AMH as a stand-alone test for PCOS diagnosis due to lack of assay standardization, absent validated cut-offs, and considerable overlap between affected and unaffected women. 1, 2
• Although AMH ≥35 pmol/L (5 ng/mL) shows 92% sensitivity and 97% specificity in research cohorts, this threshold requires further validation before clinical adoption. 1, 2

Critical Diagnostic Pitfalls to Avoid

Hormonal Contraception Interference

• Remove or allow expiration of progestin-only implants (e.g., Implanon) before testing, as they suppress the hypothalamic-pituitary-ovarian axis and render hormone levels unreliable for PCOS diagnosis. 1
• Biochemical hyperandrogenism testing requires assessment in the absence of any hormonal contraception. 1

Tests NOT to Order Routinely

• Do NOT measure insulin or C-peptide routinely; physical signs of insulin resistance (elevated BMI, acanthosis nigricans) are sufficient for assessment. 2
• Do NOT rely on LH/FSH ratio as a primary diagnostic criterion due to its low sensitivity (35-44%). 1, 4

Age-Specific Considerations

• In adolescents (<20 years or <8 years post-menarche), diagnosis relies on clinical and biochemical hyperandrogenism plus persistent menstrual irregularity 2-3 years beyond menarche; ultrasound should NOT be used due to high false-positive rates. 1

Conditions That Must Be Excluded Before Confirming PCOS

• Cushing's syndrome: Screen if buffalo hump, moon facies, hypertension, abdominal striae, central fat distribution, easy bruising, or proximal myopathies are present. 1, 2
• Androgen-secreting tumors: Consider if rapid onset of severe virilization (marked clitoromegaly, voice deepening) or testosterone >150-200 ng/dL. 1, 2
• Non-classical congenital adrenal hyperplasia: Evaluate if elevated DHEAS. 1, 2
• Primary ovarian failure: Measure FSH; levels >35-50 IU/L indicate premature ovarian insufficiency. 1, 2
• Hypothalamic amenorrhea: Consider in women with excessive exercise, low body weight, or eating disorders; characterized by low LH and absence of hyperandrogenism. 1, 2

Diagnostic Framework

You can diagnose PCOS when two of the following three Rotterdam criteria are met (after excluding mimicking conditions): 1, 5, 6

1. Oligo- or anovulation (cycle length >35 days)
2. Clinical and/or biochemical hyperandrogenism
3. Polycystic ovarian morphology on ultrasound (≥20 follicles per ovary or ovarian volume >10 mL)

Important: Clinical hyperandrogenism (hirsutism, acne, alopecia) plus irregular cycles is sufficient for diagnosis even when all laboratory values are normal, because total testosterone is abnormal in only 70% of women with confirmed PCOS. 1