Luteinizing Hormone (LH) strips offer a straightforward, at-home method for tracking the menstrual cycle and pinpointing the most fertile days. These tests operate by detecting the concentration of LH, a hormone that experiences a rapid, short-lived increase known as the LH surge. This surge is the biological signal that triggers the release of an egg from the ovary, meaning a positive test result predicts ovulation will occur soon, defining the fertile window.
Calculating When to Start Testing
Pinpointing the correct day to begin testing is crucial to avoid wasting strips and missing the surge. Timing is based on your typical menstrual cycle length, counted from the first day of bleeding to the day before the next period begins. Since ovulation typically happens about 14 days before the next period, you must estimate your ovulation day first.
For a regular 28-day cycle, ovulation is expected around day 14, so testing should begin on cycle day 11 or 12. A simple method is to subtract 17 from your average cycle length to find the earliest recommended start day, allowing lead time before the expected surge. Starting early prevents missing the entire fertile window.
If your cycle length varies, use the shortest cycle length recorded in the last six months for this calculation. This ensures you begin testing early enough to capture the surge, even if ovulation occurs earlier than average.
The Step-by-Step Testing Procedure
While the general procedure is standardized, always follow the manufacturer’s instructions. First, collect a urine sample in a clean, dry container, or use products that allow testing directly in the urine stream.
Remove the strip from its foil pouch and immerse the absorbent tip into the urine sample. Do not dip the strip past the designated maximum (MAX) line, as this can cause the test to malfunction or produce an invalid result. The strip must remain in the urine for the specified duration, often around 5 seconds, for proper absorption.
After removing the strip, immediately lay it flat on a clean, dry, non-absorbent surface. Set a timer and wait for the precise reaction time indicated in the instructions, typically five minutes. Reading the result within this specific window is necessary, as results become unreliable if read too early or too late.
Understanding and Interpreting the Results
Interpreting results involves comparing the color intensity of two lines: the control line (C) and the test line (T). The control line must always appear; its presence confirms the strip is working correctly and that enough urine was absorbed.
A negative result, indicating the LH surge has not yet occurred, is shown when the test line is lighter than the control line or absent. Since LH is always present at low levels, a faint test line is common and reflects baseline concentration, not the imminent surge.
The test is positive only when the test line is visually as dark as, or darker than, the control line. This signifies that the LH surge has been detected, signaling the ovary to release the egg. A positive result means ovulation is likely to occur within the next 12 to 36 hours.
The two most fertile days are the day of the positive test and the following day. If the control line fails to appear, the result is invalid, and the procedure must be repeated with a new strip.
Common Errors and Tips for Accuracy
To maximize reliability, avoid common mistakes, starting with the time of day you test. Unlike pregnancy tests, first-morning urine is not recommended because the hormone surge often begins early morning but takes a few hours to become detectable in urine.
Testing between 10 a.m. and 8 p.m. is often advised, and it is most effective to test at approximately the same time each day for consistent comparison. Urine concentration is another factor; drinking excessive fluids, especially in the two hours before testing, can dilute the LH concentration. Diluted urine can lead to a false negative result.
Because the LH surge can be short, sometimes lasting less than 24 hours, testing twice a day as the fertile window approaches increases the chance of catching the peak. Always read the result within the specified reaction time, as waiting too long can cause lines to fade or evaporation lines to appear, leading to misinterpretation.