Knowledge Centre
Hormones & blood testsDraft: awaiting clinical review
Luteinising hormone (LH)
The hormone whose surge triggers ovulation, and the basis of ovulation predictor kits.
Overview
A surge of LH from the pituitary triggers ovulation, usually within about 24–36 hours.
Urine ovulation predictor kits detect this surge.
What is well established
- A positive ovulation test suggests that ovulation is likely soon, but it does not confirm that ovulation has occurred.
- In PCOS, LH can be persistently raised, so ovulation tests may give misleading or repeated positive results.
Uncertain or emerging evidence
- An LH-to-FSH ratio is sometimes quoted for PCOS, but it is not part of current diagnostic criteria.
This guide is general information and does not replace advice about your own circumstances. Clinical review pending.