LH (luteinizing hormone) test: normal range

According to MedlinePlus, the LH range depends on sex, on age and, in women, on menopausal status. For women before menopause the usual interval is 5–25 IU/l, but in the middle of the menstrual cycle the level briefly rises considerably higher — it is this surge that triggers ovulation. After menopause the range is wider and higher — 7.7–58.5 IU/l — because the pituitary gland makes more LH when the ovaries no longer respond to hormones. For men from the age of 18 the interval given is 1.8–8.6 IU/l. These figures are general guides: every laboratory uses its own equipment and measurement method, so the exact reference interval should be read from your own report and the result discussed with a doctor.

In women, an LH test is used for several purposes. Most often it is used to look into the causes of infertility, when conception has not happened over a longer period, or to identify the most suitable time to conceive by watching for the LH surge in the middle of the cycle, which triggers ovulation — the release of an egg from the ovary. The test also helps to assess irregular or absent menstrual cycles, when it is unclear whether ovulation is happening at all. In addition, the LH level is used to establish whether the menopausal transition has begun or menopause has already arrived, because the LH concentration then usually rises noticeably. LH is most often assessed together with FSH and estradiol, so that the doctor can build a broader picture of the hormonal situation instead of relying on a single indicator.

In men, according to MedlinePlus, a raised LH level is most often linked to a disorder of testicular function — this may be damage to the testicles, a tumour, a past mumps infection or an injury, and also a genetic condition such as Klinefelter syndrome. In such cases the testicles no longer respond sufficiently to hormonal signals, so the pituitary gland makes more LH to compensate. A raised LH level can also indicate that the sex glands have been damaged by an autoimmune disease or by cancer treatment. To establish the exact cause, a doctor usually assesses LH together with the testosterone and FSH levels in the blood, because an LH result on its own does not reveal where exactly the cause of the disorder lies. A raised LH result should therefore always be discussed with a doctor or an endocrinologist.

A low LH level most often shows that the problem is in the pituitary gland or the hypothalamus rather than in the ovaries or the testicles themselves — these organs may be working normally but are not receiving enough of a signal to stimulate them. In women, a low LH level is sometimes linked to excessive physical exertion, inadequate nutrition, considerable stress or a low body weight, which disturb the work of the hypothalamus. When assessing a low LH level, a doctor usually also checks FSH and other pituitary hormones in order to assess overall pituitary function, and if needed suggests imaging of the pituitary gland or the hypothalamus. It is advisable to consult an endocrinologist, and for women additionally to have nutrition, weight and the intensity of physical exertion assessed.

Fasting or complicated preparation is usually not needed before an LH test, but there are a few things worth discussing with your doctor in advance. Some medicines or food supplements may need to be stopped temporarily before the test, because they can affect the result. Women who are menstruating sometimes need to have the test on a particular day of the menstrual cycle, especially when the aim is to identify the timing of ovulation or to look into cycle disturbances. It is also important to tell your doctor if you have recently had a test involving radioactive isotopes, because that can distort the results. The final preparation arrangements are always set by the doctor, taking into account the reason for the test and your state of health.

LH and FSH are two hormones made by the pituitary gland that together control the work of the ovaries and the testicles, so they are usually tested at the same time rather than separately. In women these hormones regulate the menstrual cycle and ovulation; in men, sperm production and the testosterone level. By assessing the levels of both hormones together, a doctor can better distinguish whether the cause of a disorder is in the sex glands themselves (the ovaries or the testicles) or higher up, in the pituitary gland or the hypothalamus. For example, if both hormones are raised, a problem in the glands is suspected more often, and if both are lowered — a disorder of the pituitary gland or the hypothalamus. That is precisely why an LH result is rarely assessed separately from FSH.