To describe the natural history of a condition or disease. To describe the natural history of a condition or disease. To determine effectiveness or cost effectiveness of treatments/services and/or health care products. To measure or monitor safety and harm. To measure quality of care.
According to the NMSS, attacks or flare-ups of symptoms only qualify as exacerbations if: 1  they occur at least 30 days from an earlier flare-up. 2  symptoms last for 24 hours or longer.
Ovulation Predictorâs answers: Typically, an LH surge lasts for about 24 hours. It can be shorter or longer for some women. Most women get a positive OPK for a day, two at the most. Sometimes 3, but that is not as common. You will ovulate 12-36 hours after your last positive OPK.