Low back sprain does not usually cause low-grade fever, but it may occur if the sprain is accompanied by other illnesses, medications, or mental stress. Lumbar sprain is usually a muscle injury, which will cause swelling and pain in the muscles of the lower back, and may also affect normal activities, resulting in dysfunction of the lower back. A sprain of the lower back alone does not usually cause a low-grade fever. If the lumbar sprain is accompanied by some diseases, such as cold and flu, it may cause low fever. Physiological factors, such as pain after a sprain, may be caused by excessive mental stress can be low fever phenomenon. Drugs such as atropine and antihistamines may cause hypothermia. If you have a low-grade fever with a sprained back, go to the hospital to find out the cause of the sprain and take standardized treatment under the guidance of your doctor to avoid delaying your condition.