Luteinizing Hormone (LH) is a reproductive hormone produced by the pituitary gland. It acts as a chemical messenger, playing a direct part in regulating the menstrual cycle. Many people track this hormone using at-home tests to pinpoint their fertile window. Seeing results that fluctuate daily—sometimes low, sometimes slightly elevated—can lead to confusion. These “up and down” readings can stem from normal daily physiological processes, underlying hormonal imbalances, or simple testing errors. Understanding the hormone’s natural rhythm and external influences can help clarify why its levels appear erratic.
The Standard LH Cycle and the Surge
A typical menstrual cycle features a predictable pattern of LH release. During the follicular phase, which starts on the first day of the period, LH levels remain at a steady, relatively low baseline. These low levels work with Follicle-Stimulating Hormone (FSH) to encourage the growth of ovarian follicles.
As a dominant follicle matures, it produces increasing amounts of estrogen, which signals the pituitary gland. This feedback loop culminates in a rapid, dramatic spike in LH, known as the LH surge. This surge triggers the ovary to release the mature egg, a process called ovulation, which usually occurs about 24 to 36 hours later.
Once ovulation has happened, LH levels quickly drop back down to their low basal state for the remainder of the cycle, known as the luteal phase. While a single, sharp peak is the most common pattern, some individuals naturally experience a more gradual rise, a plateau over several days, or even a biphasic surge with two peaks. These variations can sometimes be mistaken for an erratic “up and down” pattern leading up to ovulation.
Daily Physiological Factors Influencing LH Readings
The perception of fluctuating LH outside of the main surge is often rooted in the hormone’s pulsatile release. Luteinizing Hormone is not secreted continuously but rather in intermittent bursts throughout the day and night. These small bursts are part of the normal physiological process and mean that a single reading only captures the hormone level at that exact moment.
Testing at different times of the day can therefore result in minor variations in the test line intensity. The timing of testing also significantly impacts the reading since LH needs time to be processed by the body and appear in the urine. For many people, the true surge begins in the early morning but may not be detectable in the urine until several hours later.
Hydration levels are another major factor influencing daily test results, particularly when using urine-based ovulation predictor kits.
Hydration and Dilution
When a person drinks a large volume of water, the urine becomes diluted, which reduces the concentration of LH detected by the test strip. A diluted sample can cause a test to appear lighter, or negative, even if the hormone level in the blood is the same as the previous day. Conversely, concentrated urine from limited fluid intake can make a test line look darker, creating the false impression of an approaching surge.
Underlying Hormonal Conditions Creating Irregular Patterns
When LH levels consistently fluctuate over many days or cycles without a clear, sustained surge followed by ovulation, it often points to a disruption in the endocrine system. Polycystic Ovary Syndrome (PCOS) is a common cause of these genuinely erratic patterns.
Polycystic Ovary Syndrome (PCOS)
In individuals with PCOS, the pituitary gland may secrete abnormally high levels of LH relative to FSH, creating a high LH/FSH ratio. This hormonal imbalance can lead to chronically elevated LH levels or multiple, small surges that are not strong enough to trigger a full ovulation. Since the ovaries do not release a mature egg, the feedback loop is disrupted, resulting in a persistent, confusing “up and down” pattern on home tests. The test strips may appear positive or near-positive for long stretches, making it difficult to pinpoint a true fertile window.
Perimenopause and Ovarian Decline
Erratic LH fluctuations are also a hallmark of perimenopause, the transition period leading up to menopause. As ovarian function naturally declines with age, the ovaries produce less estrogen and progesterone. The pituitary gland, attempting to stimulate the slowing ovaries, responds by significantly increasing the production of both LH and FSH. These high, often unpredictable levels of LH cause the hormone to appear elevated or fluctuating wildly on tests, reflecting the body’s struggle to maintain regular cycles.
Common Errors in LH Testing and Interpretation
In many cases, the perceived fluctuation is not physiological but a result of errors in the testing process itself. Home ovulation tests require strict adherence to instructions for accurate interpretation.
Timing and Evaporation Lines
One frequent mistake is reading the test result outside of the designated time window, which is usually between five and thirty minutes. If a test is read after the maximum time limit, a faint line may appear as the test dries, known as an evaporation line, which can be mistaken for a minor rise in LH. Conversely, if the test is read too early, the chemical reaction may not be complete, leading to a falsely light or negative result.
Subjective Interpretation
The subjective interpretation of line darkness is another major source of perceived fluctuation. An ovulation test is only considered positive when the test line is as dark as or darker than the control line. Seeing a faint test line simply means that some LH is present, which is normal for most of the cycle, and this faintness should not be interpreted as a mini-surge.
False Positives
A positive result can occasionally be misleading if the test strip picks up human Chorionic Gonadotropin (hCG), the pregnancy hormone, which shares a chemical similarity with LH. This chemical cross-reactivity can produce a false positive and lead to confusion about an unexpected LH spike.