Kidney infection (pyelonephritis) is a specific type of urinary tract infection (UTI) that generally begins in your urethra or bladder and travels up into your kidneys. If not treated properly, kidney infection can permanently damage your kidneys or spread to your bloodstream and cause a life-threatening infection. Prompt medical attention is required.

The kidneys are an important component of the urinary system. These organs process blood; filter out waste; and flush out waste as urine, which travels to the bladder through tubes called ureters and is eliminated from the body through the urethra. The kidneys also keep certain chemicals balanced and produce hormones that help maintain blood pressure, red blood cell count, and healthy bones.

Chronic glomerulonephritis is a slowly progressive disease characterized by inflammation of the glomeruli, which results in sclerosis, scarring and, eventually, renal failure. This disorder usually develops insidiously and without symptoms, often over many years.

Causes of kidney infection

The pain caused by kidney stones occurs when a stone becomes lodged in the ureter, the slender tube that connects the kidney with the bladder. Urine flow is then blocked, which causes urine to back up into the kidney. The kidney then swells and enlarges, stretching the pain-sensitive capsule, or thin covering around it.

Pyelonephritis is an inflammation of one or both kidneys with variable manifestations. It may be acute, relapsing or chronic. The complications of this disorder are hypertension, chronic infection, renal insufficiency and renal failure. The course is extremely variable but typically the chronic disease progresses extremely slowly, with patients having adequate renal function for more than 20 years after onset.

Kidney infection typically occurs when bacteria enter your urinary tract through the urethra and begin to multiply. Bacteria from an infection elsewhere in your body also can spread through your bloodstream to your kidneys. Kidney infection is unusual through this route, but it can occur in some circumstances - for instance, when a foreign body, such as an artificial joint or heart valve, gets infected. Rarely, kidney infection results after kidney surgery.

Most kidney infections develop as a complication from cystitis (bladder infection). Bacteria causing cystitis sometimes travel up to infect a kidney. The bacteria are usually those which live in your bowel. They sometimes travel from the anus, up the urethra into the bladder, and cause infection. (Note: cystitis is common, and most people with cystitis do not develop a kidney infection.)
Strep infection is the most common cause of glomerulonephritis. Pyelonephritis can be caused by any of the organisms that cause lower urinary tract infection (E. coli, klebsiella, etc.)

Conditions such as pregnancy, diabetes, cancer, kidney stones, and abnormalities of the urinary tract can lower your ability to fight off the bacteria that cause kidney infections. Foley catheters (tubes inserted through the urethra to drain the bladder) can also lead to infection if left in place for extended periods. Women sometimes contract kidney infections when bacteria get into the urinary tract following sex.

Some kidney infections develop without a bladder infection. This is sometimes due to a problem in the kidney. For example, you are more prone to kidney infections if you have a kidney stone or an abnormality of a kidney.
Bacteria in the urine don't always signify an infection. Some people, especially older adults, may have bacteria in the bladder that don't cause any signs or symptoms or harm, and therefore doesn't require treatment. This condition is known as asymptomatic bacteriuria.