The 8 Blood Tests That Confirm PCOS - And What Your Numbers Mean

One in five Indian women in their reproductive years has PCOS. Yet most of them receive a folder of hormone test results, a brief "your hormones are imbalanced" from the doctor, and almost no explanation of what any of the numbers actually mean.

This is that explanation.

Why No Single Test Can Confirm PCOS

PCOS is diagnosed using the Rotterdam criteria - a set of three features, of which you need at least two:

1. Irregular or absent periods
2. Evidence of high androgens (either blood tests or physical symptoms like acne and excess hair growth)
3. Polycystic-appearing ovaries on ultrasound

This means blood tests alone cannot confirm PCOS. They are used to support the diagnosis, rule out other conditions that look similar, and understand the specific hormonal pattern in your case. Two women can both have PCOS and have completely different test results.

Quick-Reference: Normal Ranges at a Glance

All values should be drawn on days 2-5 of the menstrual cycle (early follicular phase) unless otherwise noted.

The 8 Tests and What They Measure

1. LH - Luteinizing Hormone

Normal range (follicular phase, days 2-5 of cycle): 2-15 IU/L

LH triggers ovulation. In PCOS, the pituitary gland often secretes LH in abnormal pulses, disrupting the normal ovulation cycle. LH alone is not diagnostic - it must be read alongside FSH.

2. FSH - Follicle-Stimulating Hormone

Normal range (follicular phase): 3-10 IU/L

FSH stimulates follicle development in the ovaries each month. In PCOS, FSH is often normal but the ratio of LH to FSH is skewed.

3. LH:FSH Ratio - The Number That Matters More Than Either Alone

This is the most diagnostic of the three.

The critical thing to understand: individual LH and FSH values can both fall within their normal ranges while the ratio is clearly abnormal. This is why many women are told "your hormones are normal" after looking at LH and FSH in isolation - when the ratio is the actual signal.

Timing matters enormously: this test should be drawn on days 2-5 of your menstrual cycle (early follicular phase). If drawn at any other time, the values are much harder to interpret.

4. Total and Free Testosterone

Normal range for women:

• Total testosterone: below 0.5 ng/mL (or below 50 ng/dL)
• Free testosterone: below 2.2 pg/mL

Testosterone is present in women at low levels and is essential for libido, bone density, and muscle. In PCOS, the ovaries produce excess testosterone (hyperandrogenism), which drives symptoms like acne, oily skin, excess facial and body hair, and hair thinning at the scalp.

Free testosterone (the fraction not bound to proteins) is more clinically relevant than total testosterone because it is the biologically active form. Some women with PCOS have normal total testosterone but elevated free testosterone - which is why testing both matters.

5. DHEAS - Dehydroepiandrosterone Sulfate

Normal range: 35-430 mcg/dL (varies significantly with age - younger women are at the higher end)

DHEAS comes primarily from the adrenal glands (not the ovaries). Elevated DHEAS in a woman with suspected PCOS suggests an adrenal component to the androgen excess. It is also used to rule out adrenal tumours, which can mimic PCOS.

6. Prolactin

Normal range: 4-23 ng/mL

Prolactin is not elevated in PCOS - it is tested to rule out hyperprolactinemia (a pituitary disorder) and hypothyroidism, both of which can cause irregular periods and look superficially like PCOS. An elevated prolactin level shifts the diagnosis away from PCOS entirely.

7. Fasting Insulin and HOMA-IR

HOMA-IR interpretation:

• Below 1.9: Normal insulin sensitivity
• 1.9-2.9: Early insulin resistance
• Above 2.9: Significant insulin resistance (HOMA-IR above 2.5 is the commonly used cut-off)

HOMA-IR is calculated from fasting insulin and fasting glucose: (fasting insulin Ã- fasting glucose) ÷ 405 (when using mg/dL).

This test does not diagnose PCOS but is critical for understanding your metabolic risk. Approximately 70% of Indian women with PCOS have insulin resistance. Insulin stimulates the ovaries to produce excess testosterone and disrupts LH pulsing - so in many cases, insulin resistance is the underlying driver of the hormonal chaos. Identifying and treating insulin resistance (with lifestyle changes, metformin, or both) is often the most effective approach.

South Asian women, including Indians, are particularly prone to insulin resistance at lower BMI values than Western populations - meaning a "normal" weight Indian woman with PCOS may have significant insulin resistance that a doctor focused on obesity might miss.

8. AMH - Anti-Mullerian Hormone

Suggestive of PCOS: above 3.5-4.0 ng/mL (some labs use different thresholds)

AMH is secreted by small follicles in the ovaries. In PCOS, there are more small follicles than normal (the "polycystic" part of the name), so AMH is typically elevated. AMH above 3.5 ng/mL in the right clinical context supports a PCOS diagnosis.

AMH is also used to assess ovarian reserve - meaning it tells you roughly how many eggs remain. For women concerned about fertility, AMH is an important piece of information beyond just its PCOS utility.

The Pattern That Points to PCOS

No single test confirms PCOS, but a pattern does. The classic hormonal picture:

• LH:FSH ratio above 2:1
• Elevated free testosterone or DHEAS
• Normal or suppressed FSH
• Elevated AMH
• Elevated HOMA-IR (common but not universal)
• Normal prolactin and TSH (ruling out other conditions)

Because thyroid disorders and PCOS frequently produce overlapping symptoms - irregular periods, fatigue, weight changes, hair problems - most doctors will order a thyroid function test alongside the PCOS panel. Undiagnosed hypothyroidism can masquerade as PCOS, and the two conditions can coexist.

Women with PCOS also have elevated cardiovascular risk, particularly higher triglycerides and lower HDL cholesterol. Once PCOS is confirmed, reviewing your lipid profile as part of your ongoing care is worthwhile.

What Normal Values Do Not Rule Out

This is perhaps the most important point in this entire post. Because PCOS is diagnosed on a pattern rather than a single threshold, a woman can have:

• LH in the normal range
• Testosterone in the normal range
• Normal FSH

...and still have PCOS, if two of the Rotterdam criteria are met clinically. Blood tests support the diagnosis; they do not override clinical judgment.

Questions to Ask Your Doctor

1. Were my LH and FSH drawn on days 2-5 of my cycle, and what is the LH:FSH ratio specifically?
2. Was my free testosterone tested, or only total testosterone?
3. Is my HOMA-IR within normal range, and if not, does that affect my treatment plan?
4. Should I be tested for thyroid function and prolactin to rule out other causes?
5. Given my AMH level and age, what does my ovarian reserve look like if I want to consider pregnancy in the future?

Must Read

• AMH Test and Ovarian Reserve - How AMH testing complements PCOS blood work for fertility assessment
• HOMA-IR Insulin Resistance Test - Why insulin resistance testing is often recommended alongside PCOS blood work

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