Blood Tests for PCOS: What to Test and What Results Mean
PCOS (polycystic ovary syndrome) is the most common hormonal disorder in women of reproductive age, affecting up to 15% of women. Diagnosis requires blood tests alongside clinical criteria — here is what to test and how to interpret the results.
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Get My Score →The Diagnostic Criteria and Where Blood Tests Fit
PCOS is diagnosed using the Rotterdam criteria, which requires two of three features: irregular or absent ovulation (irregular periods), clinical or biochemical signs of excess androgens (testosterone), and polycystic ovaries on ultrasound. Blood tests assess the hormonal and metabolic dimensions of the diagnosis and help identify which aspects of PCOS are most prominent — which guides management.
Key Blood Tests for PCOS
| Test | What to Look For in PCOS |
|---|---|
| Total testosterone | Elevated above 70 ng/dL (confirms biochemical hyperandrogenism) |
| Free testosterone / SHBG | High free testosterone; SHBG often low (elevated insulin suppresses SHBG) |
| DHEAS | Mildly elevated in ~50% of PCOS (adrenal androgen contribution) |
| LH:FSH ratio | Often greater than 2:1 or 3:1 in PCOS (elevated LH relative to FSH) |
| Fasting glucose and insulin (HOMA-IR) | Insulin resistance present in 65–80% of women with PCOS |
| HbA1c | Check for pre-diabetes and diabetes — markedly elevated risk in PCOS |
| TSH | Rule out hypothyroidism, which can cause similar symptoms |
| Prolactin | Rule out hyperprolactinaemia, which disrupts ovulation |
| 17-hydroxyprogesterone | Rule out non-classical congenital adrenal hyperplasia (can mimic PCOS) |
PCOS Hormone Panel — What to Request
Insulin Resistance: The Central Metabolic Driver
65–80% of women with PCOS have insulin resistance — and high insulin is mechanistically central to the condition. Elevated insulin directly stimulates androgen production in the ovaries and suppresses SHBG (sex hormone-binding globulin), increasing the free fraction of testosterone. This is why insulin-sensitising interventions — particularly exercise, dietary modification, and metformin — often improve all aspects of PCOS simultaneously. Fasting insulin and HOMA-IR are the most useful blood tests to assess this dimension.
What the LH:FSH Ratio Shows
In PCOS, the pulsatile release of GnRH from the hypothalamus is disrupted — LH pulses become more frequent and larger relative to FSH. This elevated LH:FSH ratio (often above 2:1 or 3:1) stimulates ovarian androgen production and impairs follicle maturation, contributing to anovulation. However, the LH:FSH ratio is normal in many women with PCOS — its absence does not exclude the diagnosis.
Insulin Resistance Is the Driver in Most PCOS Cases
Hyperinsulinaemia stimulates the ovaries to produce excess androgens — this is the central mechanism in most PCOS. Even lean women with PCOS often have significant insulin resistance. Treating IR with diet (low-refined carbohydrate, weight management) and exercise directly addresses the hormonal dysfunction — and often restores cycle regularity without medication.
Testing to Rule Out Similar Conditions
Several conditions can present similarly to PCOS. Hypothyroidism causes irregular periods and metabolic changes — TSH should be checked in all cases. Hyperprolactinaemia (elevated prolactin) from a pituitary adenoma suppresses ovulation — prolactin should always be tested. Non-classical congenital adrenal hyperplasia (NCAH) causes androgen excess from the adrenal glands rather than ovaries — screened with a morning 17-hydroxyprogesterone level. These conditions require different treatment from PCOS.
Medical Disclaimer
This article is for educational purposes only and does not constitute medical advice. Reference ranges, supplement dosages, and nutritional information mentioned are general educational guidance from published research—not personalised recommendations. Do not use this content to self-diagnose or self-treat any condition. Always consult a qualified healthcare provider before making any changes to your health regimen, medications, or supplements.
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