Identification of the LH surge by measuring intact and total immunoreactivity in urine for prediction of ovulation time

OBJECTIVES: In our earlier study, we separated three different molecular forms of urinary LH-ir (U-LH-ir) by gel filtration and identified them by immunoassay in urine from regularly menstruating women on periovulatory days. U-LH-ir is composed of intact luteinizing hormone (LH), its free beta-subunit (LHβ), and the core fragment of LHβ (LHβcf), the latter two establishing the non-intact portion of LH-ir. The aim was to determine whether timing of ovulation can be improved by detecting different molecular forms of U-LH-ir in women of reproductive age. METHODS: We determined intact and total U-LH-ir in 14 regularly menstruating women on consecutive periovulatory days during the menstrual cycle. Non-intact LH-ir was calculated as the arithmetic difference between total and intact LH-ir. In addition, LH-ir was determined in both serum and urine from four of the women throughout the menstrual cycle. RESULTS: During the LH surge, U-LH-ir consisted mainly of intact LH and presented with an abrupt increase. Intact U-LH-ir dropped rapidly within 1 day after the surge, reaching baseline levels at the end of the luteal phase. In contrast, LHβcf in urine increased further 1 day after the surge. After this, most of the U-LH-ir consisted of LHβcf and it remained strongly elevated (over fivefold compared to intact LH) for the first 3 days after the LH surge, moderately elevated (over threefold) thereafter until day + 5, and mildly elevated until day + 7. CONCLUSIONS: Total and non-intact LH-ir are potential add-on characteristics which can be utilized in ovulation predictor kits to measure LH-ir in urine beyond the LH surge during a broader time frame, thereby paving the way for more precise prediction of the timing of ovulation than that obtained with currently available products.