Diagnosing Polycystic Ovary Syndrome (PCOS)
PCOS diagnosis requires at least two of three criteria: clinical or biochemical hyperandrogenism, oligo-/anovulation, and polycystic ovarian morphology on ultrasound, after excluding other causes of androgen excess. 1, 2, 3
Clinical History Assessment
Document specific menstrual patterns, as cycle length >35 days indicates chronic anovulation 1. The onset pattern of androgen excess symptoms is critical—gradual onset suggests PCOS, while rapid onset with severe hyperandrogenism raises concern for androgen-secreting tumors 1, 2. Review all medications, particularly exogenous androgens, which can mimic PCOS 1, 2. Obtain family history of cardiovascular disease and diabetes, as these conditions cluster in PCOS families 1, 2.
Physical Examination Findings
Examine for clinical hyperandrogenism: hirsutism, acne, male-pattern alopecia, and clitoromegaly 1, 2. Calculate BMI and waist-hip ratio to assess central obesity 1, 2, 3. Look specifically for acanthosis nigricans on the neck, axillae, under breasts, and vulva, which indicates insulin resistance 3. Screen for Cushing's syndrome features including buffalo hump, moon facies, and abdominal striae 1, 2.
Laboratory Testing
Androgen Assessment
Total testosterone measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS) is the single best initial biochemical marker, with 74% sensitivity and 86% specificity. 2, 3 This method is superior to direct immunoassays, showing 92% specificity versus 78% for immunoassays 2, 3.
Calculated free testosterone using the Vermeulen equation has the highest sensitivity at 89% with 83% specificity 2. Measure sex hormone-binding globulin (SHBG) to calculate free testosterone accurately 1, 2.
Exclusion of Other Disorders
Measure TSH to exclude thyroid disease 1, 3. Check prolactin levels to rule out hyperprolactinemia 1, 3. Measure 17-hydroxyprogesterone to exclude non-classic congenital adrenal hyperplasia 2, 3. Consider dexamethasone suppression testing if Cushing's syndrome is suspected based on physical findings 2, 3.
Metabolic Screening
Perform a 2-hour oral glucose tolerance test with 75g glucose load in all women with PCOS, regardless of BMI, as insulin resistance occurs independently of body weight. 1, 3 Women with PCOS have 31-35% prevalence of impaired glucose tolerance and 7.5-10% prevalence of type 2 diabetes 4. Obtain a fasting lipid profile to screen for dyslipidemia 1, 3.
Ultrasound Evaluation
Technical Specifications
Transvaginal ultrasound with ≥8 MHz transducer frequency is the optimal imaging approach in adults. 5, 1, 2 Transabdominal ultrasound is acceptable when transvaginal approach is not feasible, but focus on ovarian volume rather than follicle counts due to lower resolution 5, 1.
Diagnostic Thresholds
The presence of ≥20 follicles (2-9mm diameter) per ovary is the gold standard ultrasonographic marker, with 87.64% sensitivity and 93.74% specificity. 5, 1, 2 When accurate follicle counting is difficult, ovarian volume >10 mL serves as an alternative diagnostic threshold 5, 1, 2.
Document three dimensions of each ovary and calculate volume 1. Ensure no corpus luteum, cyst, or dominant follicle is present, as these can confound the diagnosis 3.
Critical Pitfall
Up to one-third of reproductive-aged women without PCOS have polycystic ovarian morphology on ultrasound, making ultrasound findings alone insufficient for diagnosis. 1, 2 This is why the Rotterdam criteria require two of three features, not just ultrasound findings.
Age-Specific Considerations
Do not use ultrasound as a first-line diagnostic tool in adolescents <8 years post-menarche or <20 years of age due to poor specificity and high false-positive rates. 2, 3 In this population, rely on clinical and biochemical hyperandrogenism plus menstrual irregularity persisting 2-3 years beyond menarche 2, 3.
For obese adolescents where ultrasound is limited, MRI pelvis without IV contrast may provide reproducible ovarian volume assessment, though follicle counts have only moderate interobserver agreement 5, 3.
Alternative Imaging When Ultrasound Is Limited
MRI pelvis without IV contrast can be considered when ovaries cannot be adequately visualized by ultrasound, particularly in obese patients 5, 1. MRI can provide reliable ovarian volume assessment but is less reliable for follicle counting 5.
Anti-Müllerian Hormone (AMH) Considerations
Do not use serum AMH levels as a single test for PCOS diagnosis despite emerging evidence. 1, 2 AMH lacks standardization across assays, has no established cut-offs, shows significant overlap between women with and without PCOS, and varies with age 2. AMH levels are naturally high in adolescence and decline with age, requiring age-specific reference ranges that don't yet exist 2.
Common Diagnostic Pitfalls
Hormonal contraceptives, including progestin-only implants like Implanon, suppress the hypothalamic-pituitary-ovarian axis and make hormone levels unreliable for PCOS diagnosis 2. Remove or allow contraceptive implants to expire before testing 2.
Transient multifollicular appearance can occur after discontinuing birth control and does not represent true PCOS 2. Excessive exercise patterns can cause hypothalamic suppression and amenorrhea, mimicking PCOS 2.
Chronic anovulation in PCOS increases the risk of endometrial cancer, requiring appropriate follow-up with endometrial assessment in women with persistent bleeding. 1, 4
Differential Diagnosis to Exclude
Rule out androgen-secreting tumors (characterized by rapid onset and severe hyperandrogenism), Cushing's syndrome, non-classic congenital adrenal hyperplasia, acromegaly, primary ovarian failure, and hyperprolactinemia before confirming PCOS 1, 2, 3.