LH (luteinising hormone): what it is, what it tells you and when it’s tested

LH is a hormone made by the pituitary, the same small gland that makes FSH. In women it surges mid-cycle and triggers ovulation. In men it tells the testes to make testosterone.

When it’s tested

Doctors order it when periods are irregular or absent, when a pregnancy is slow to come, or when they suspect polycystic ovary syndrome or an early menopause. In men, usually together with testosterone, when that is low or there are fertility problems.

In women it is often done early in the cycle, with FSH and oestradiol. To tell whether you are in menopause, hormone tests are usually not needed over 45.

It is not a test for people who feel well, which is why Rosa does not test it. Instead it looks at what often goes with cycle problems: TSH for the thyroid, and insulin and blood sugar, which are often worth watching in polycystic ovary syndrome.

What it tells you, and what it does not

Read with FSH and oestradiol, LH helps show where a cycle problem starts. If FSH and LH are high, the ovaries respond less, as in menopause. If they are low or normal with a low oestradiol, the brake often comes from the brain: stress, low weight, a lot of exercise.

In polycystic ovary syndrome LH is sometimes a little high, but not always. That is why on its own it is not enough for a diagnosis.

A single value says little: LH changes a lot with the day of the cycle.

That is why it is read together with other tests:

Normal LH levels

There is no single normal value. In women LH stays low for most of the cycle, then surges briefly mid-cycle to trigger ovulation. After menopause it stays high.

That is why every lab prints different intervals per phase: follicular, ovulatory peak, luteal and postmenopausal. Read your value against the interval for the right phase, on your own report.

In men the values are steadier. There too, the interval on your report is what counts.

If your LH is high or low

The LH surge and ovulation tests

The ovulation tests you buy at the pharmacy look for the LH surge in urine. The surge usually comes one to two days before ovulation.

They are handy but not perfect: sometimes they show a surge that is not there, or miss it. In polycystic ovary syndrome, with LH already a little high, they can be positive without ovulation.

To know whether you ovulated, doctors rely more on progesterone, a week before your expected period.

What can skew the result

A few things change LH without saying much about the ovaries or testes. It helps to know them before your blood test.

When to worry

Talk to your doctor or gynaecologist if:

Frequently asked questions

What is the LH surge? A fast, short-lived rise in LH mid-cycle. It triggers ovulation, usually one to two days later. Ovulation tests look for it in urine.

High LH and polycystic ovaries: is there a link? In polycystic ovary syndrome LH is sometimes a little high, but not always, and a high LH is not enough for a diagnosis. The diagnosis needs two of three signs: irregular periods, too many male hormones, polycystic ovaries on ultrasound or a high anti-Müllerian hormone.

Does the LH to FSH ratio still matter? It used to be watched closely. Today it is not one of the criteria for polycystic ovary syndrome. Your doctor reads LH and FSH together, with oestradiol and your periods.

What does a low LH mean? Often it is the pill, or the body holding back the cycle because of stress, low weight or a lot of exercise. More rarely it is the pituitary. If FSH is low too and your periods stop, talk to your doctor.

Does Rosa test LH? No. Rosa measures TSH, insulin, blood sugar and ferritin, which are useful when your cycle changes. If your doctor wants LH, they order it separately.

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