PCOS diagnosis involves several markers: LH, FSH, testosterone, AMH and insulin. How to read each one, and what the pattern means together.
Polycystic ovary syndrome, PCOS, is one of the most common hormonal conditions in women of reproductive age, affecting around 1 in 10 in the UK. Despite its prevalence, it is frequently misdiagnosed or dismissed, partly because no single blood test confirms it, and partly because reference ranges for hormonal markers are often poorly calibrated for the PCOS population.
The most widely used diagnostic criteria are the Rotterdam criteria, which require two of the following three features:
Blood tests are used to assess the second criterion and to rule out other conditions that can mimic PCOS.
In PCOS, LH, luteinising hormone, is often elevated relative to FSH, follicle stimulating hormone. An LH to FSH ratio above 2 to 1 or 3 to 1 is a classic finding, though it is not present in all cases and is not required for diagnosis. Both hormones should ideally be tested on day 2 to 5 of the menstrual cycle, or at any time if periods are absent.
| Marker | Typical range | PCOS pattern |
|---|---|---|
| LH, follicular phase | 2 to 15 IU/L | Often elevated, with a high LH to FSH ratio. |
| FSH, follicular phase | 3 to 10 IU/L | Normal or low normal. |
| LH to FSH ratio | About 1 to 1 | Often above 2 to 1 in PCOS. |
Elevated testosterone is one of the biochemical hallmarks of PCOS. However, total testosterone can be within the reference range even when free testosterone, the biologically active fraction, is elevated. This is because PCOS is often associated with low sex hormone binding globulin, SHBG, which means more testosterone is unbound and active.
Ask for both total testosterone and SHBG if possible. The free androgen index is total testosterone divided by SHBG, times 100. A free androgen index above 5 in women is generally considered elevated.
AMH is produced by ovarian follicles and is a marker of ovarian reserve. In PCOS, AMH is typically elevated, often two to three times higher than in women without the condition, because PCOS involves an increased number of small antral follicles. An AMH above 10 to 12 pmol/L in a woman of reproductive age is consistent with PCOS, though ranges vary between labs.
Insulin resistance is present in approximately 70% of women with PCOS, regardless of weight. However, standard NHS blood tests do not routinely include fasting insulin. HbA1c and fasting glucose are more commonly tested and can identify impaired glucose regulation, but they are less sensitive for early insulin resistance than a fasting insulin level or an oral glucose tolerance test.
Several conditions can mimic PCOS and should be excluded:
Standard reference ranges for hormones are derived from the general population and do not account for the specific patterns seen in PCOS. A testosterone result of 2.0 nmol/L might be within the female reference range, typically 0.3 to 2.5 nmol/L, but could still be associated with significant symptoms if SHBG is low. Similarly, an AMH of 8 pmol/L might be normal but is significantly lower than the 15 to 25 pmol/L commonly seen in PCOS.
This is why reading PCOS blood results requires looking at the pattern across multiple markers, not just whether each individual result is flagged.
PCOS is a pattern, not a number. biomarkr keeps your hormone markers together and shows how each one moves over time. Free for your first year.
Join early access →Criteria and guidance in this article are drawn from the Rotterdam criteria, NHS sources and NICE Clinical Knowledge Summaries. Your own lab report ranges always take precedence.
Educational purposes only · not medical advice · always speak to your GP or a qualified clinician about your results