An ovulation test (also sometimes called an OPK, which stands for ovulation predictor kit) is a test that detects the presence and concentration of luteinizing hormone (LH) in your urine. About 12 – 36 hours before ovulation, there is a brief surge in LH levels. (The length of time between the beginning of the LH surge and ovulation varies from woman to woman.) The LH surge sends a message to your ovaries that it’s time to release an egg: ovulation! When you get a positive ovulation test, it means that ovulation is likely imminent.