Diagnostic Criteria for PCOS
PCOS is diagnosed in adults when two of three Rotterdam criteria are met: androgen excess (clinical or biochemical), ovulatory dysfunction, or polycystic ovaries on ultrasound—but only after excluding mimicking disorders. 1
Core Diagnostic Algorithm for Adults
The diagnosis requires a systematic approach:
Step 1: Identify Two of Three Features
You need any two of the following 1:
- Androgen excess: Either clinical (hirsutism, acne, alopecia) or biochemical (elevated testosterone or other androgens)
- Ovulatory dysfunction: Oligomenorrhea or amenorrhea
- Polycystic ovaries: ≥12 follicles measuring 2-9 mm OR ovarian volume >10 mL in at least one ovary (without a dominant follicle >10 mm) 1
Critical point: If a patient already meets two criteria clinically (e.g., irregular periods plus hirsutism), you do not need to perform androgen assays or ultrasound 1. Document which features led to the diagnosis.
Step 2: Mandatory Exclusion Testing
All women must be screened for conditions that mimic PCOS 1:
- TSH (thyroid disease causes irregular cycles)
- Prolactin (hyperprolactinemia presents with amenorrhea/hirsutism)
- 17-hydroxyprogesterone (17-OHP) (non-classic congenital adrenal hyperplasia occurs in 1.5-6.8% of hyperandrogenic patients) 1
Step 3: Extended Evaluation When Indicated
For women with amenorrhea, virilization, or atypical features (proximal muscle weakness suggesting Cushing's, frontal bossing suggesting acromegaly), pursue additional testing to exclude other diagnoses 1.
Special Population: Adolescents
The diagnostic criteria differ substantially in adolescents. Diagnosis requires both of the following 1:
- Clinical and/or biochemical hyperandrogenism (after excluding other pathologies)
- Persistent oligomenorrhea (defined relative to years post-menarche)
Do NOT use polycystic ovarian morphology or anovulatory symptoms for diagnosis in adolescents—these are normal developmental findings 1. Anovulatory cycles comprise 85% of cycles in year one post-menarche, 59% in year three, and 25% by year six 1. Many healthy adolescents have polycystic ovarian morphology in early post-menarchal years 2.
Adolescents meeting only one criterion should be labeled "at risk" of PCOS and followed longitudinally 3.
Special Population: Perimenopausal/Menopausal Women
No validated diagnostic criteria exist for this age group 1. A presumptive diagnosis can be made based on well-documented history of oligomenorrhea and hyperandrogenism during reproductive years. Polycystic ovarian morphology on ultrasound provides supportive evidence but is less likely present in menopausal women 1.
Common Pitfalls to Avoid
Overdiagnosis in adolescents: Normal pubertal physiology mimics PCOS. Irregular cycles are physiologic for 2 years post-menarche. Transient acne alone should not define hyperandrogenism 1.
Missing exclusion diagnoses: Non-classic CAH is found in up to 6.8% of hyperandrogenic patients—always check 17-OHP 1.
Unnecessary testing: If clinical criteria are already met (irregular periods + hirsutism), additional androgen assays or ultrasound add no diagnostic value 1.
Using ultrasound in adolescents: This leads to overdiagnosis and should be avoided 3.
Phenotypic Considerations
Different phenotypes carry different risks 1:
- Hyperandrogenism associates more strongly with metabolic abnormalities
- Irregular menses and polycystic ovarian morphology associate more with infertility
Document the specific features present, as this guides risk stratification and management priorities.