How would you know you have a kidney infection?

Pyelonephritis: An infection of the kidney (pyelonephritis) results in severe back pain, high fever and nausea/vomiting. Unlike an infection only involving the bladder, the ascension of bacteria into the kidney is a dangerous event. If you have these symptoms it is important to see a doctor and have your urine tested. Untreated pyelonephritis can result in permanent kidney damage, blood infection or shock.