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Probably the most common cause of kidney pain is a kidney infection, known as pyelonephritis, where dull, aching upper back pain is experienced at one side, around the level of the lowest ribs, together with symptoms such as fever and blood in the urine. Kidney stones may cause severe and sudden pain, however, as this occurs when the stone has left the kidney and is moving along the tube, or ureter, that leads to the bladder, it could be argued that this is not technically kidney pain. It is important to remember that some conditions which are serious enough to cause kidney failure do not lead to pain, and that pain may appear to come from the kidneys but other diseases may be causing the pain around the same area. Sometimes people assume lower back pain is kidney pain, but the kidneys are located slightly higher, tucked inside the lower ribs at the back of the torso. Other possible causes of kidney pain include blood clots, tumors, a urinary tract infection and any kidney disease which results in death of renal tissue.
The condition known as atherosclerosis, where arteries become narrowed, may lead to the formation of a blood clot in the renal artery which supplies the kidney. Loss of the blood supply to some or all of the kidney tissue causes sudden pain and possibly blood in the urine. Kidney tumors can also cause blood in the urine, but the pain experienced due to tumors tends to develop more gradually. Hydronephrosis is another condition which may cause kidney pain. In hydronephrosis, an obstruction of the flow of urine from the kidney by a tumor, stone or kink in the urinary tract leads to back pressure of urine and a swollen kidney.
Diagnosis of kidney pain may be carried out using tests such as urine dipsticks and urine cultures. Urine dipsticks change color to indicate abnormalities in the urine, such as changes in acidity and concentration, or the presence of blood, protein, bacteria and other substances. A kidney infection could lead to blood and protein being found in the urine, and a urine culture, where microbes from a urine sample are allowed to grow, could be used to determine the type of bacteria involved.
X-rays and scans of the kidneys and urinary system can help diagnose the cause of kidney pain. A sample of kidney tissue, known as a biopsy, may be taken to look for signs of disease. Some kidney disorders, such as polycystic kidney disease, cause high blood pressure as well as pain, and blood pressure may be measured during investigations. Blood tests may be taken to check whether waste products are accumulating in the blood due to loss of kidney function. Treatment of kidney pain varies depending on the cause, but most often the pain resolves when the underlying condition is treated successfully.