Blood test results

Lh

Luteinising hormone, from the pituitary, which triggers ovulation and testosterone production. Varies by sex and cycle phase.

What Lh measures

Luteinizing hormone, or LH, is made by the pituitary gland at the base of the brain, and it acts on the reproductive organs. In women it triggers ovulation, surging sharply around the middle of the menstrual cycle to release an egg, and it rises to higher baseline levels after menopause. In men it stimulates the testes to produce testosterone. Because LH works as part of a feedback loop, it is usually read alongside FSH and the relevant sex hormones such as estradiol or testosterone rather than on its own. Where a menstrual cycle is present, the timing of the sample within that cycle strongly shapes what the number means, so your clinician interprets LH in the context of your sex, cycle day, and overall picture.

What a high Lh can mean

A higher-than-usual LH often suggests the ovaries or testes are less responsive, so the pituitary signals more strongly to compensate. In women, a raised LH commonly reflects menopause or the transition toward it, or reduced ovarian reserve. A pattern of LH raised relative to FSH is sometimes seen in polycystic ovary syndrome (PCOS), though this is only one piece of that picture. In men, an elevated LH can point to a testicular cause of reduced function, where the testes make less testosterone despite a strong pituitary signal.

• Menstrual changes, hot flushes, or fertility difficulties
• Low libido, fatigue, or other signs of reduced sex-hormone activity

Because the mid-cycle surge and cycle timing can lift a single reading, when the sample was taken matters. A high LH is interpreted alongside FSH, sex hormones, and your symptoms by your clinician.

What a low Lh can mean

A lower-than-usual LH often suggests the signal from the brain itself is reduced, pointing toward a pituitary or hypothalamic cause rather than the reproductive organs. This can happen with significant stress, very low body weight or under-eating, or intense or prolonged exercise, all of which can quiet the reproductive signalling. Certain pituitary conditions that lower the gland's output can also reduce LH, sometimes affecting other pituitary hormones at the same time.

• Irregular, infrequent, or absent menstrual periods
• Low libido or other signs of reduced sex-hormone activity

Because LH sits within a feedback loop, a low value is read together with FSH and the relevant sex hormones to understand where in the chain the change lies. On its own it is not a diagnosis, and your clinician weighs it against your history, symptoms, and other results.

Educational only — not medical or diagnostic advice. One marker is a single data point; interpret it alongside your history and other results, and consult a qualified clinician about your health.