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Bacteria can spread from the bladder to the kidneys either by moving up the ureter or by invading the kidneys from the bloodstream to cause a kidney infection (acute pyelonephritis).
Most people who have acute pyelonephritis have a fever and flank pain on the side of the body where the infected kidney is located. The back hurts just below the place where the ribs meet the spine.
A person who has a bladder infection can also have a fever and flank pain. So those symptoms don't tell the healthcare professional whether a person has a bladder infection or the much more serious kidney infection.
A person with a urinary tract infection who feels very ill and has a fever of about 100.4° to 104°F, shaking chills, and flank (see above) pain and tenderness is fairly likely to have a kidney infection (acute pyelonephritis). If a blood test shows a high number of white blood cells (leukocytes) and a urine test reveals clumps of white blood cells in the urine, the person almost definitely has a kidney infection.
If the kidney infection does not seem too serious, the healthcare professional will prescribe antibiotics that can be swallowed (oral antibiotics). The type of antibiotic prescribed will be one that works well against the kinds of bacteria that cause urinary tract infections.
Complications of urinary tract infections
A complication is a development of an illness that makes matters worse.
Most people who have a urinary tract infection don't develop complications. Complications are more likely to occur in people who have some sort of anatomic abnormality of the urinary system or who have a catheter inserted in the bladder.
Men who have prostatitis and people who have urinary stones may have repeated (recurrent) urinary tract infections.
A spinal cord injury may paralyze the urinary bladder so that it can't empty. Urinary tract infections may come back time and time again if the bladder does not empty readily.
Complicated urinary tract infections are serious illnesses. A person who has a complicated urinary tract infection, such as a complicated kidney infection (complicated pyelonephritis), may have to go to the hospital to receive antibiotics through a needle inserted into a vein (intravenous, or I.V., antibiotics).
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