LH is made by the pituitary gland, a pea-sized gland under the brain, in response to a signal from the hypothalamus called GnRH. It travels in the blood to the testes, where it switches on the Leydig cells that produce testosterone. The name comes from its role in women, where it triggers ovulation and forms the corpus luteum, but in men its job is simply to keep testosterone coming.
The system is a feedback loop, much like a thermostat. When testosterone and oestradiol are low, the pituitary releases more LH; when they are high, it cuts back. That is why LH is so useful as a detective: its level tells you which part of the loop is struggling.
LH has a partner hormone, follicle-stimulating hormone (FSH), which drives sperm production. Doctors usually measure the two together.
What does LH do in men?
LH is the pituitary's instruction to the testes to make testosterone. Without enough LH, healthy testes still cannot produce normal testosterone levels.
Testosterone made inside the testes under LH's influence is also needed locally for sperm production, working alongside FSH. So LH matters for fertility even though FSH gets more of the credit. LH is also released in pulses rather than a steady stream, so a single reading is a snapshot and is always read alongside testosterone rather than on its own. If you are trying for a baby, our guide to the sperm regeneration timeline explains how long changes take to show up.
What do high or low LH levels mean?
LH only makes sense next to a testosterone result. Low testosterone with high LH points to a problem in the testes; low testosterone with low or normal LH points to the pituitary or hypothalamus.1
The European Male Ageing Study used exactly this approach in 3,369 men aged 40 to 79. It found 11.8% had the secondary (brain-driven) pattern, 2.0% the primary (testicular) pattern, and 9.5% a compensated pattern, where testosterone was normal but LH was raised to keep it there.1
- Low testosterone, high LH: primary hypogonadism1
- Low testosterone, low or normal LH: secondary hypogonadism1
- Normal testosterone, high LH: compensated hypogonadism1
Why does LH matter when testosterone is low?
Because the cause changes what happens next. The Endocrine Society recommends further tests to find the reason once low testosterone is confirmed, and LH is central to that.2
In the ageing study, a body mass index of 30 or more was strongly linked with the secondary pattern, while older age was linked with the primary pattern.1 A secondary pattern also prompts doctors to consider pituitary causes, which is why prolactin is often checked at the same time. Gonadotropins, the family that includes LH, also rose over time within men followed in the Massachusetts Male Aging Study.3
How does testosterone therapy affect LH?
Testosterone from outside the body tells the pituitary to stop making LH and FSH, so the testes' own output drops. It is effective enough to have been tested as a male contraceptive.4
In a World Health Organization study of 271 healthy men, weekly injections of 200 mg testosterone enanthate stopped sperm appearing in the semen of 65% of them within six months.4 That is why guidelines advise against starting testosterone therapy in men who are planning to father a child soon.2 If fertility matters to you, raise it with your doctor before any hormone treatment starts.
Common questions
When is an LH blood test done?
Usually after low testosterone has been confirmed on repeat morning tests, to work out whether the testes or the pituitary are at the root of it.2 It is also part of many male fertility work-ups.
Does LH change with age?
It tends to rise. In the Massachusetts Male Aging Study, pituitary gonadotropins increased over time within the same men, a sign that the testes need more prompting to keep testosterone up.3
Can I boost LH on my own?
LH is not a sensible do-it-yourself target. If it is low because of excess weight, poor sleep or a medicine, the fix is to address that. Specialists sometimes use medicines that stimulate the pituitary or mimic LH, but those need proper diagnosis and monitoring.
Read more on this
How testosterone changes after 40 (and what actually helps)
How long does it take sperm to regenerate?
Sources
- Tajar A, et al. Characteristics of secondary, primary, and compensated hypogonadism in aging men: evidence from the European Male Ageing Study. J Clin Endocrinol Metab. 2010;95(4):1810-1818. PubMed
- Bhasin S, et al. Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2018;103(5):1715-1744. PubMed
- Feldman HA, et al. Age trends in the level of serum testosterone and other hormones in middle-aged men: longitudinal results from the Massachusetts Male Aging Study. J Clin Endocrinol Metab. 2002;87(2):589-598. PubMed
- World Health Organization Task Force on Methods for the Regulation of Male Fertility. Contraceptive efficacy of testosterone-induced azoospermia in normal men. Lancet. 1990;336(8721):955-959. PubMed
Not medical advice. Written by Eric Stephens from the research cited above; not reviewed by a doctor. If something worries you, see a GP.