An ovulation kit is used to predict when a woman is most fertile by detecting the surge in luteinizing hormone (LH) that precedes ovulation. To use one, collect a urine sample and dip the test strip or place the absorbent tip in the urine for the time specified in the instructions. A positive result is typically indicated when a second line appears that is as dark as or darker than the control line, meaning ovulation is likely to occur within 24-36 hours.