Luteinizing Hormone LH Tests Explained by Dallas FEMM Instructor

Jennifer Taylor
Dec 28, 2025
2 min read

Updated: Feb 12

Luteinizing Hormone LH Explained

Luteinizing hormone, most widely known as LH, is released by the brain signaling the ovaries to ovulate. This occurs when estrogen reaches peak, sending a signal to the brain to launch LH. This hormone surges for about twelve hours. During this time the ovaries finish maturing the egg in the dominant follicle. Within 24 to 36 hours of the LH surge, ovulation occurs.

Why should I test for LH surge?

Testing for the LH surge can help a woman pinpoint that ovulation is occurring soon. While LH surge is a strong predictor of ovulation, it is not a guarantee that ovulation will occur. For this reason it is important to monitor other biomarkers such as cervical mucus. Please note that LH is NOT the start of fertility. It is most common that the fertile window has already started by the time a positive LH test is observed.

Women find LH surge to be very helpful when trying to conceive or avoid pregnancy.

When do I start testing LH?

Begin testing on cycle day 7 or the point of change (POC), If cycles are irregular and a pattern has not been established, start testing on cycle day 7. Once a clear pattern has emerged, then starting LH test on POC may begin. Continue testing LH daily until a positive reading is observed. There is no need to continue testing after a positive LH test.

Test at the approximate same time frame every day. Avoid first morning urine as that is too concentrated. Mid morning to early evening are great times to test. If cycles are erratic, some women choose to test twice a day. It is up to you.

How do I read the LH test results?

Unlike pregnancy tests, a LH test is positive when the control line and test line are the same darkness. The test line will appear during most tests, however if it is lighter than the control, then it is NEGATIVE.