PCOS Blood Tests: What Labs to Order

Polycystic Ovary Syndrome is diagnosed using the Rotterdam criteria, which require at least two of three features: irregular or absent periods, clinical or biochemical signs of excess androgens, and polycystic ovaries on ultrasound. Blood tests play a critical role in establishing the biochemical piece of that puzzle.

The core labs for a PCOS workup include:

• Total Testosterone — the single most important androgen to measure. Women with PCOS typically show levels above 45–50 ng/dL, though reference ranges vary by lab.
• DHEA-S — an adrenal androgen that helps rule out adrenal tumors or congenital adrenal hyperplasia as the source of excess androgens.
• LH and FSH — a reversed LH:FSH ratio (LH higher than FSH) is suggestive of PCOS, though this pattern isn't present in every patient.
• Estradiol — helps assess ovarian function and is part of the standard fertility hormone panel.
• TSH — thyroid disorders mimic PCOS symptoms (weight gain, irregular periods, fatigue) and must be ruled out.

Your doctor may also order a 17-hydroxyprogesterone level drawn in the early morning to rule out non-classical congenital adrenal hyperplasia, which presents very similarly to PCOS.

Blood should ideally be drawn in the morning (before 10 AM) during days 2–5 of your menstrual cycle for the most accurate hormone interpretation. If you aren't having periods, the blood can be drawn any day.

Hormones in PCOS don't operate in isolation — they form an interconnected web. Elevated insulin drives the ovaries to produce more testosterone. That excess testosterone suppresses ovulation, which keeps progesterone low and estrogen relatively unopposed. Understanding these relationships helps you interpret your results.

Testosterone: Normal total testosterone in women is roughly 15–46 ng/dL. Values above 50 ng/dL in the context of irregular periods strongly suggest PCOS. Very high levels (above 150–200 ng/dL) warrant evaluation for an androgen-secreting tumor.

LH and FSH: In a normal cycle, FSH is slightly higher than LH in the follicular phase. In PCOS, LH is often 2–3× higher than FSH (e.g., LH 15 mIU/mL vs FSH 5 mIU/mL). However, up to 40% of PCOS patients have a normal ratio, so this test alone can't rule it in or out.

DHEA-S: Normal range for women is approximately 35–430 µg/dL depending on age. Mildly elevated DHEA-S is common in PCOS. Markedly elevated levels (above 700 µg/dL) suggest an adrenal source and need further workup.

SHBG (Sex Hormone-Binding Globulin): This protein binds testosterone and makes it inactive. Insulin resistance lowers SHBG, which means more free (active) testosterone is available. A low SHBG in the context of normal-ish total testosterone can still indicate androgen excess.

Up to 70% of women with PCOS have some degree of insulin resistance — regardless of body weight. This makes metabolic testing just as important as hormone testing. Insulin resistance is the underlying driver of many PCOS symptoms and is the most modifiable risk factor.

Fasting Insulin: This is the most sensitive early marker of insulin resistance. A normal fasting insulin is generally below 10 µIU/mL. Values above 15 suggest resistance, and above 20 indicate significant metabolic dysfunction. Importantly, fasting glucose can remain normal for years while insulin climbs, so testing glucose alone misses early insulin resistance.

Hemoglobin A1c: This reflects your average blood sugar over 2–3 months. Normal is below 5.7%, prediabetes is 5.7–6.4%, and diabetes is 6.5% or above. The American Diabetes Association recommends screening all PCOS patients at diagnosis and every 1–3 years thereafter.

Lipid Panel: PCOS increases the risk of dyslipidemia. A common pattern is elevated triglycerides, low HDL, and small dense LDL particles. This "metabolic syndrome" pattern further increases cardiovascular risk.

Vitamin D: Studies consistently show that 67–85% of women with PCOS are vitamin D deficient (below 30 ng/mL). Low vitamin D is associated with worsened insulin resistance and may impair ovulation. Supplementing to bring levels above 40 ng/mL has shown metabolic benefits in clinical trials.

After your initial diagnosis, follow-up blood work frequency depends on your treatment plan and goals:

• If starting metformin or inositol: Recheck fasting insulin and A1c at 3 months to assess response. A meaningful drop in fasting insulin (e.g., from 22 to 12 µIU/mL) confirms the medication is working.
• If trying to conceive: Monitor LH, FSH, estradiol, and progesterone per your fertility specialist's protocol. A progesterone level above 3 ng/mL mid-luteal phase (day 21) confirms ovulation occurred.
• If on spironolactone for acne/hair growth: Check a potassium level and basic metabolic panel at 1 month and then every 6–12 months, since spironolactone can raise potassium.
• Annual screening: All women with PCOS should have a lipid panel and A1c checked annually. Fasting insulin every 1–2 years is also reasonable to track metabolic trajectory.
• Vitamin D: If supplementing, recheck after 3 months to confirm levels have risen above 30 ng/mL (ideally 40–60 ng/mL).

Tracking your labs over time is one of the most powerful things you can do. PCOS is a lifelong condition, and longitudinal data helps you and your provider fine-tune treatment.