How PCOS is Diagnosed
PCOS is diagnosed using the Rotterdam criteria, which requires at least 2 of 3 features: oligo/anovulation, clinical or biochemical hyperandrogenism, and polycystic ovarian morphology on ultrasound—but only after excluding other causes of androgen excess. 1
Core Diagnostic Criteria
The diagnosis requires meeting at least 2 of the following 3 criteria 1:
- Oligo- or anovulation (menstrual cycle length >35 days) 1
- Clinical or biochemical hyperandrogenism 1
- Polycystic ovarian morphology on ultrasound 1
Clinical Assessment
History Taking
- Menstrual history: Document cycle length, with >35 days suggesting chronic anovulation 1
- Onset and duration of androgen excess signs: Gradual onset after menarche is typical for PCOS 1, 2
- Medication review: Check for exogenous androgens or medications like spironolactone that can mask diagnostic features 1, 3
- Family history: Obtain cardiovascular disease and diabetes history 1
- Lifestyle factors: Assess diet, exercise, alcohol use, and smoking 1
Physical Examination
- Signs of hyperandrogenism: Look for acne, balding, hirsutism, and clitoromegaly 1
- Body measurements: Calculate BMI and waist-hip ratio 1
- Signs suggesting alternative diagnoses: Buffalo hump, moon facies, hypertension, and abdominal striae suggest Cushing's syndrome 1
Laboratory Evaluation
First-Line Tests
- Total testosterone (TT) and free testosterone (FT): First-line tests for biochemical hyperandrogenism 3
- DHEA-sulfate: Screen for adrenal androgen excess 4
- 17-hydroxyprogesterone: Exclude non-classic congenital adrenal hyperplasia 1, 2
Additional Screening
- TSH and prolactin: Rule out thyroid disease and prolactin disorders 1, 2
- Fasting glucose and lipid profile: Screen for metabolic complications 1
Ultrasound Criteria
Adult Women (≥18 years)
- Gold standard marker: Follicle number per ovary (FNPO) ≥20 follicles (sensitivity 87.64%, specificity 93.74%) 1
- Alternative markers: Ovarian volume >10 mL or follicle number per single cross-section when accurate counting is not possible 1
- Technical requirements: Use transvaginal ultrasound with ≥8 MHz transducer frequency 1
Adolescents (<20 years, at least 1 year post-menarche)
- Avoid ultrasound as primary diagnostic tool due to high false-positive rates 1
- Rely on clinical and biochemical hyperandrogenism plus menstrual irregularity 1
Critical Differential Diagnoses to Exclude
Rapid onset or severe hyperandrogenism should raise suspicion for alternative diagnoses 1, 2:
- Androgen-secreting tumors: Characterized by rapid onset and very high serum androgen levels 1, 2
- Cushing's syndrome: Look for buffalo hump, moon facies, hypertension, abdominal striae 1
- Non-classic congenital adrenal hyperplasia: Elevated basal or ACTH-stimulated 17-OHP levels 1, 2
- Hyperprolactinemia: Recent onset oligomenorrhea with mild hyperandrogenism 2
- Thyroid disease: Screen with TSH 1
Important Diagnostic Pitfalls
Medication Interference
If a patient is on spironolactone, conduct evaluation before starting therapy or after a 2-4 week washout period 3. Spironolactone can:
- Lower serum testosterone levels, masking biochemical hyperandrogenism 3
- Improve menstrual regularity, concealing oligo/amenorrhea 3
- Reduce hirsutism scores, hiding clinical hyperandrogenism 3
If washout is not possible, place greater emphasis on ultrasound findings of polycystic ovarian morphology, as these are less affected by medication 3.
Age-Related Considerations
Polycystic ovarian morphology is seen in approximately 22% of normal women, making ultrasound findings alone insufficient for diagnosis 5. This is particularly problematic in adolescents, where ultrasound has poor specificity 1.
Emerging Diagnostic Tools
Anti-Müllerian Hormone (AMH) shows promise as an alternative to ultrasound, with significantly higher levels in PCOS patients 1. However, current limitations include lack of standardization across assays and absence of established cut-offs, preventing its routine clinical use 1.