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

Laboratory Tests for Suspected Polycystic Ovary Syndrome

Order total testosterone and free testosterone by liquid chromatography-tandem mass spectrometry (LC-MS/MS), thyroid-stimulating hormone, prolactin, a 2-hour 75-gram oral glucose tolerance test, and a fasting lipid panel as your core laboratory work-up for any woman with suspected PCOS. 1

First-Line Androgen Assessment

• Measure total testosterone using LC-MS/MS as your primary androgen marker, which demonstrates 74% sensitivity and 86% specificity for detecting hyperandrogenism in PCOS. 1
• Measure free testosterone (or calculate it using the Vermeulen equation from total testosterone and SHBG), which shows superior sensitivity of 89% with 83% specificity. 1
• LC-MS/MS assays provide 92% specificity compared to only 78% for direct immunoassays, making the assay method critical—avoid direct immunoassays due to high false-positive rates. 1

Mandatory Exclusion Tests

• Measure TSH to rule out thyroid disease as a cause of menstrual irregularity. 1
• Obtain a morning resting serum prolactin level to exclude hyperprolactinemia; values >20 µg/L are abnormal and women with PCOS have a 3.15-fold increased risk of elevated prolactin. 1
• 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

Second-Line Androgen Tests (Only When Primary Tests Are Normal)

• Measure androstenedione if total and free testosterone are normal but clinical suspicion remains high; values >10 nmol/L raise suspicion for an adrenal or ovarian androgen-secreting tumor. 1
• Measure DHEAS to evaluate for non-classical congenital adrenal hyperplasia, particularly if androstenedione is elevated; age-adjusted thresholds are ≥3800 ng/mL for ages 20-29 and ≥2700 ng/mL for ages 30-39. 1

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, limiting its diagnostic utility. 1
• Measure mid-luteal phase progesterone; concentrations <6 nmol/L indicate anovulation. 1

Metabolic Screening (Required for All PCOS Patients)

• Perform a 2-hour oral glucose tolerance test with 75 grams of glucose to screen for impaired glucose tolerance and type 2 diabetes, regardless of body mass index, because insulin resistance occurs independently of weight in PCOS. 1, 2
• Do not substitute hemoglobin A1C or fasting glucose alone for the oral glucose tolerance test—the 2-hour OGTT is superior for detecting impaired glucose tolerance in PCOS women. 3
• Measure a fasting lipid panel including total cholesterol, LDL, HDL, and triglycerides to assess cardiovascular risk. 1
• Calculate body mass index and waist-hip ratio; a waist-hip ratio >0.9 indicates truncal obesity and heightened metabolic risk. 1
• Consider measuring fasting glucose and insulin to calculate a glucose/insulin ratio; a ratio >4 suggests reduced insulin sensitivity. 1

Tests You Should NOT Order

• Do not measure insulin or C-peptide routinely—physical signs of insulin resistance (BMI, acanthosis nigricans) are sufficient, and routine measurements are not recommended by ACOG. 4
• Do not use anti-Müllerian hormone (AMH) as a diagnostic test for PCOS or as a substitute for ultrasound, because assay standardization is lacking, validated cut-offs do not exist, and there is considerable overlap between affected and unaffected women. 1, 2

Additional Exclusion Tests Based on Clinical Presentation

• Screen for Cushing syndrome if the patient has buffalo hump, moon facies, hypertension, abdominal striae, central fat distribution, easy bruising, or proximal myopathies—use a dexamethasone suppression test. 1, 2
• Measure 17-hydroxyprogesterone if you suspect non-classical congenital adrenal hyperplasia based on ethnicity or severe hyperandrogenism. 2
• Measure FSH to rule out primary ovarian failure, particularly in women in their third decade presenting with amenorrhea; FSH >50 mIU/mL signifies primary gonadal failure. 1
• Consider androgen-secreting tumors if there is rapid onset of symptoms, severe hirsutism, very high testosterone levels, or marked virilization (clitoromegaly, voice deepening). 1

Critical Diagnostic Pitfalls

• Do not rely on ultrasound alone—isolated polycystic ovarian morphology is found in 17-22% of asymptomatic women and does not establish PCOS diagnosis without other criteria. 1
• Do not use ultrasound for diagnosis in women <8 years post-menarche (<8 years gynecological age) because multifollicular ovaries are physiologically normal during this period. 1, 2
• If the patient already has both irregular menstrual cycles AND clinical/biochemical hyperandrogenism, ultrasound is not necessary for diagnosis according to Rotterdam criteria, though it will identify the complete phenotype. 1, 2
• Functional hyperprolactinemia can mimic PCOS with oligomenorrhea, amenorrhea, and hirsutism—always exclude this before confirming PCOS. 1
• Hypothalamic amenorrhea from excessive exercise or low body weight can present with menstrual irregularity without hyperandrogenism—evaluate lifestyle factors carefully. 1

Monitoring After Diagnosis

• Repeat oral glucose tolerance testing every 1-2 years based on family history of diabetes and BMI, and yearly in women with impaired glucose tolerance, because progression rates from normal glucose tolerance to impaired glucose tolerance and then to type 2 diabetes can be 5-15% within 3 years. 5
• Repeat fasting lipid profiles annually. 1
• Monitor body weight, blood pressure, and cardiovascular risk factors every 6-12 months. 1