What it measures
- LH (luteinising hormone)
What is luteinising hormone?
LH is made by the pituitary gland. Mid-cycle, a surge of LH triggers the ovary to release an egg; ovulation tests sold in pharmacies detect this surge in urine. In men, LH tells the testes to make testosterone.
Why measure LH?
Measured early in the cycle alongside FSH, LH helps assess how your ovaries and pituitary gland are working. In some people with polycystic ovary syndrome, LH is high compared with FSH. For a complete hormone picture, see our Fertility Package.
Who it’s for
- Trying to conceive
- Irregular periods or suspected PCOS
- Low testosterone in men
How to prepare
- Drink plenty of water beforehand; it makes the sample quicker and easier to take.
- You don’t need to fast.
- If you have periods, book for day 2–5 of your cycle (day 1 is the first day of bleeding).
- Stop biotin (vitamin B7) supplements 48 hours before, as biotin can affect hormone and thyroid results.
Luteinizing Hormone (LH) Blood Test: your questions
Is this the same as an ovulation test?
Not quite. Home ovulation kits detect the mid-cycle LH surge in urine. This blood test measures your baseline LH, usually early in your cycle, to assess hormone balance.
Information on this page is general and doesn’t replace advice from your GP, midwife or consultant. If you feel unwell or are worried about symptoms, contact your GP, call NHS 111 or, in an emergency, 999.