Understanding Your PCOS Blood Tests

One of the most common frustrations women face during their PCOS journey is walking out of a blood draw with a stack of results and no idea what any of it means. Doctors often order the right tests but spend very little time explaining what each one measures, why it was ordered, or what your specific numbers suggest. This guide breaks down every blood test commonly involved in PCOS diagnosis and monitoring, in plain language.

A note before we start: reference ranges vary between laboratories, and interpreting results requires clinical context. This guide explains what each test measures and why it matters for PCOS. It is not a substitute for a conversation with your doctor about your specific results.

Hormone tests

LH (Luteinizing Hormone) and FSH (Follicle-Stimulating Hormone). These two hormones work together to regulate your menstrual cycle and ovulation. In many women with PCOS, LH is elevated relative to FSH, sometimes at a 2:1 or 3:1 ratio. This imbalance contributes to disrupted ovulation. However, an elevated LH:FSH ratio is not required for a PCOS diagnosis and is not present in all cases.

Total testosterone. The primary androgen marker. Elevated total testosterone is one of the most common biochemical findings in PCOS and contributes to symptoms like acne, hirsutism, and hair loss. However, total testosterone alone does not tell the full story because much of it may be bound to SHBG and therefore inactive.

Free testosterone. This measures the testosterone that is not bound to proteins and is biologically active. In PCOS, free testosterone is often a more sensitive marker than total testosterone because SHBG tends to be low, leaving more testosterone available to act on tissues.

SHBG (Sex Hormone Binding Globulin). A protein that binds to testosterone and makes it inactive. SHBG is commonly low in PCOS, particularly in women with insulin resistance. Low SHBG means more free, active testosterone even when total testosterone appears normal.

Free Androgen Index (FAI). A calculated value: FAI = (total testosterone / SHBG) x 100. Often considered more clinically meaningful than either value alone because it captures the relationship between available androgens and the protein that controls them.

DHEAS (Dehydroepiandrosterone Sulphate). An androgen produced by the adrenal glands rather than the ovaries. Elevated DHEAS suggests an adrenal contribution to hyperandrogenism. This distinction matters because management approaches may differ depending on whether androgen excess is ovarian, adrenal, or both in origin.

AMH (Anti-Mullerian Hormone). Produced by the small follicles in the ovaries. AMH is often elevated in PCOS, reflecting the higher number of small antral follicles characteristic of polycystic ovarian morphology. Some specialists use AMH as an additional diagnostic marker, though it is not formally part of the Rotterdam criteria. AMH is also relevant for fertility assessment.

Metabolic tests

Fasting insulin. A direct measure of how much insulin your pancreas is producing. Elevated fasting insulin is a strong indicator of insulin resistance, which affects an estimated 50 to 70% of women with PCOS regardless of body weight. This test requires a fasting blood draw (8 to 12 hours without food).

Fasting glucose. Measures the amount of sugar in your blood after fasting. Combined with fasting insulin, it is used to calculate HOMA-IR. On its own, fasting glucose can appear normal even when significant insulin resistance is present, which is why fasting insulin is essential.

HOMA-IR (Homeostatic Model Assessment of Insulin Resistance). A calculated index: HOMA-IR = (fasting insulin x fasting glucose) / 405 (when using mg/dL for glucose and mIU/L for insulin). Values above approximately 2.5 suggest insulin resistance, though thresholds can vary. This single number gives a clearer picture of insulin resistance than either insulin or glucose alone.

HbA1c (Glycated Haemoglobin). Reflects your average blood sugar control over the past 2 to 3 months. It is a standard diabetes screening tool and is particularly important for women with PCOS who have insulin resistance. An HbA1c between 5.7% and 6.4% indicates prediabetes.

Lipid panel. Total cholesterol, LDL (“bad” cholesterol), HDL (“good” cholesterol), and triglycerides. Cardiovascular risk assessment is recommended for all women with PCOS per Endocrine Society and ESHRE guidelines, not just those with visible metabolic features.

Exclusion tests

These tests rule out other conditions that can mimic PCOS symptoms. They are an essential part of the diagnostic workup.

TSH (Thyroid-Stimulating Hormone). Screens for thyroid disorders. Both hypothyroidism and hyperthyroidism can cause menstrual irregularity, fatigue, weight changes, and mood symptoms. Thyroid dysfunction is in the PCOS differential diagnosis and must be excluded.

Free T4. Pairs with TSH for a more complete thyroid assessment. If TSH is abnormal, free T4 helps determine the type and severity of thyroid dysfunction.

Anti-TPO antibodies. The primary marker for Hashimoto's thyroiditis (autoimmune thyroid disease), which has an elevated prevalence in women with PCOS compared to the general population. Worth testing if thyroid symptoms are present or TSH is borderline.

Prolactin. Screens for hyperprolactinaemia, which can cause irregular periods and amenorrhoea. Elevated prolactin can mimic PCOS and must be ruled out.

17-Hydroxyprogesterone (17-OHP). Screens for non-classical congenital adrenal hyperplasia (CAH), a genetic condition that causes adrenal androgen excess and can closely mimic PCOS. Endocrine Society guidelines specifically recommend this test as part of the PCOS workup.

Additional tests

Vitamin D (25-OH). Deficiency is highly prevalent in women with PCOS and has been associated with worse insulin sensitivity, higher androgen levels, and lower mood. Testing is recommended, and supplementation when deficient is guideline-supported.

Vitamin B12. Relevant for women on long-term metformin, which can deplete B12 stores. Monitoring is recommended if you have been taking metformin for more than 6 months.

Ferritin. Measures iron stores. Haemoglobin (the standard blood count test) can appear normal while ferritin is low, meaning you can be iron-depleted without being technically anaemic. Relevant for women with PCOS who have heavy periods.

hsCRP (high-sensitivity C-Reactive Protein). A marker of chronic low-grade inflammation, which is part of PCOS pathophysiology in many women. Also used alongside the lipid panel for cardiovascular risk assessment.

Cortisol. An adrenal stress hormone. Tested in some cases to rule out Cushing's syndrome or to assess adrenal function when DHEAS is elevated. Not part of routine PCOS testing but may be ordered by an endocrinologist.

Liver function (ALT, AST, GGT). Non-alcoholic fatty liver disease (NAFLD, now called MASLD) is a recognised PCOS comorbidity, particularly in women with insulin resistance. Liver function tests can flag this early.

What to do with your results

The most important thing is to keep copies of all your results and track them over time. A single snapshot tells you where things stand today; longitudinal data shows you whether your management approach is working.

If your doctor does not explain your results clearly, ask. You have the right to understand what was tested, what the results mean, and what (if anything) should happen next. If specific tests from this list were not included in your workup, you can ask for them.

Alaia's test results tracker lets you log blood work and ultrasound findings in one place, view them alongside your symptom data over time, and include them in your appointment prep reports so your doctor sees the full picture.

This content is for informational purposes only. Reference ranges vary between laboratories, and results should always be interpreted by a qualified healthcare provider in the context of your clinical picture.