Diagnosing PCOS: Tests, Criteria, and What to Expect

Introduction

Despite being extremely common, PCOS is often diagnosed late — an average of 2+ years after symptom onset in many studies. This delay is partly due to variable presentation, unfamiliarity with diagnostic criteria among non-specialist clinicians, and the misattribution of symptoms (irregular periods "normalised," acne attributed to lifestyle, weight gain attributed to diet). This article describes the diagnostic pathway, investigations, and criteria clearly and practically.

When to Suspect PCOS

Consider evaluation for PCOS in any reproductive-age woman with:

Step 1: History and Physical Examination

A thorough history includes: menstrual pattern since menarche, any pregnancies and outcomes, symptoms of androgen excess, weight history, medication history, family history, and psychosocial impact. Physical examination: BMI and waist circumference; blood pressure; acanthosis nigricans (velvety skin thickening at neck/axillae — a sign of insulin resistance); assessment for hirsutism (mFG score); acne; scalp hair thinning; signs of other endocrine conditions (thyroid, Cushing\'s).

Step 2: Excluding Other Causes First

Before confirming PCOS, other conditions causing similar features must be excluded — as these require different management:

• Thyroid disease: TSH should be checked in all suspected PCOS. Both hypothyroidism (irregular cycles
• weight gain) and hyperthyroidism (irregular cycles
• anxiety) can mimic PCOS.
• Hyperprolactinaemia: Elevated prolactin causes irregular cycles and occasionally amenorrhoea. Measure prolactin (ensure sample is taken in morning
• not after stress).
• Late-onset congenital adrenal hyperplasia (CAH): Due to 21-hydroxylase deficiency; causes hyperandrogenism and irregular cycles. Screen with early-morning 17-hydroxyprogesterone.
• Cushing syndrome: Cortisol excess causes weight gain
• hypertension
• hirsutism
• irregular cycles. Screen with 24h urine free cortisol if clinically suspected.
• Androgen-secreting tumours: Rare
• but suggested by very rapid onset of severe virilisation. Testosterone >5 nmol/L should prompt tumour search.

Step 3: Biochemical Investigations

• Free testosterone (or calculated free testosterone from total testosterone + SHBG): The most sensitive biochemical marker. LC-MS/MS assay preferred.
• SHBG: Low in insulin resistance/hyperandrogenism.
• DHEA-S: Elevated in adrenal hyperandrogenism.
• LH and FSH: Elevated LH:FSH ratio (>2:1) supports PCOS but is not diagnostic alone.
• AMH (anti-Müllerian hormone): Elevated in PCOS
• reflecting the large antral follicle cohort. Now accepted as a diagnostic criterion surrogate in the 2023 guideline.
• Fasting glucose and insulin (HOMA-IR) or OGTT: Screen for insulin resistance and impaired glucose tolerance.
• Lipid profile: Assess cardiovascular risk.
• TSH
• prolactin
• 17-OHP: Exclusion tests (see above).

Step 4: Pelvic Ultrasound

Transvaginal ultrasound (TVS) is more sensitive than transabdominal. Polycystic ovarian morphology: ≥20 follicles per ovary (updated threshold in 2023 guideline, using high-resolution probes) or increased ovarian volume >10 mL. Importantly, ultrasound is less reliable in adolescents (multifollicular ovaries are common in the 2–3 years post-menarche) and in women taking hormonal contraceptives. The 2023 guideline allows AMH to replace ultrasound in adults when assay is standardised.

Step 5: Apply Diagnostic Criteria

Rotterdam criteria: 2 of 3 required. In adults: hyperandrogenism (clinical or biochemical) + anovulation/oligomenorrhoea + PCOM/elevated AMH.

Special note on adolescents (within 8 years of menarche): Both hyperandrogenism AND irregular cycles are required (polycystic morphology is not sufficient as a standalone criterion in adolescents, due to normal developmental variation).

After Diagnosis: Telling Patients

Many women feel overwhelmed, confused, or relieved to have a name for their symptoms. Key messages to communicate: PCOS is manageable; lifestyle is powerful; it does not mean you cannot have children; metabolic monitoring is important but many complications are preventable; the condition evolves over time. Providing written information and follow-up appointments to discuss implications helps patients process the diagnosis.

References: 2023 International PCOS Guideline; Rotterdam Criteria 2003; ACOG Practice Bulletin on PCOS; Teede H et al., Nat Rev Endocrinol 2023.