Luteinizing Hormone (LH) is always present in your urine, but the concentration fluctuates dramatically. LH is a powerful reproductive hormone continually produced by the body. A small, baseline amount constantly circulates in the bloodstream and is subsequently excreted in the urine. This constant presence is necessary to regulate reproductive functions. However, these baseline levels are usually too low to trigger a positive reading on at-home tests, which are designed to detect a specific, temporary spike in concentration.
What is Luteinizing Hormone
Luteinizing Hormone is a chemical messenger produced by the pituitary gland, located at the base of the brain. This hormone plays a central role in puberty, sexual function, and reproduction. In females, LH stimulates the ovaries to produce sex hormones like estrogen and progesterone.
LH’s primary function is to support the development and final maturation of the egg follicle. Early in the cycle, LH stimulates cells to produce androgens, which are converted into estrogen with the help of Follicle-Stimulating Hormone (FSH). This process prepares the egg for release. In males, LH signals the testes to produce testosterone, which is required for sperm production.
The Menstrual Cycle and Baseline Levels
Throughout most of the menstrual cycle, Luteinizing Hormone remains at a relatively low and steady concentration, referred to as the baseline level. During the follicular phase, which starts on the first day of the period, LH levels are typically low. These low levels are maintained by a biological feedback loop involving the ovaries and the brain.
As the egg follicle matures, it releases increasing amounts of estrogen, which initially suppresses LH production. Once estrogen production from the dominant follicle crosses a certain high threshold, the feedback loop reverses, causing a rapid and massive hormonal increase known as the “LH surge”. This surge occurs approximately 24 to 36 hours before the egg is released, with LH levels peaking significantly higher than the baseline. The peak LH level triggers the final event of ovulation, releasing the mature egg from the ovary.
Identifying the LH Surge with Urine Tests
Urine-based ovulation predictor kits (OPKs) are designed to detect the dramatic and temporary rise in Luteinizing Hormone that precedes ovulation. These tests do not measure the exact amount of hormone present but instead use a predetermined concentration threshold to register a positive result.
Because a small amount of LH is always present in the urine, a faint line may often appear on test strips, but this is considered a negative result. A test is only considered positive when the test line is as dark as, or darker than, the control line, indicating that the LH concentration has crossed the specific detection threshold. This threshold is usually set high enough, often between 25 and 30 milli-International Units per milliliter (mIU/mL) in the urine, to ignore the constant low baseline levels.
To ensure accuracy, it is generally recommended to test around the same time each day and limit fluid intake for a few hours beforehand, as diluted urine can temporarily lower the hormone concentration below the detection threshold, potentially causing a false negative. The detection of the surge can signal that ovulation is likely to occur within the next 24 to 36 hours.
Medical Conditions That Influence LH Readings
Certain medical conditions and external factors can cause a person to have consistently elevated LH levels that interfere with the typical reading of urine tests.
Polycystic Ovary Syndrome (PCOS)
Polycystic Ovary Syndrome (PCOS) is a common endocrine disorder that often results in mildly elevated baseline LH levels due to a hormonal imbalance. This can lead to frequent false-positive results on ovulation predictor kits because the baseline concentration is already near or above the test’s detection threshold. In such cases, the urine test may indicate a surge when the actual ovulatory event is not occurring.
Perimenopause
During the transition to menopause, known as perimenopause, the ovaries begin to function less effectively. In response, the pituitary gland attempts to stimulate the ovaries by producing higher amounts of Luteinizing Hormone. These chronically high levels cause LH levels to rise and remain high, which can also lead to ambiguous or consistently positive test results.
Fertility Treatments
Furthermore, some fertility treatments involve injections of human Chorionic Gonadotropin (hCG), a hormone that is structurally very similar to LH, which can cause ovulation tests to show a positive result even when no natural surge has occurred.