What Is a Kidney Infection (Pyelonephritis)?

Isn't a kidney infection just a bladder infection that got worse? Roughly, yes — and that "got worse" part is exactly why it matters. Pyelonephritis is the medical name for an infection that has reached one or both kidneys, usually by travelling up from the bladder. The short video above, "CVA Tenderness USMLE," runs just over a minute and shows the back examination clinicians use when they suspect this — a useful window into how a kidney infection is checked, rather than just described.

How is a kidney infection different from a bladder infection?

A bladder infection tends to stay low: burning when you pass urine, needing to go often, and pressure low in the tummy. Once infection reaches a kidney, the picture usually widens. People commonly feel pain in the side or back — the flank — and may develop fever, chills, nausea, or simply feel quite unwell. Our guide to a urinary tract infection (UTI) covers the lower-tract symptoms in detail, and the video linked there, "Urinary Tract Infection," lists back or lower-abdominal pain or pressure among the symptoms to watch for. That overlap is the point: back pain alongside urinary symptoms and fever is a combination to take seriously, not to wait out.

What does the back-tenderness check in the video actually show?

The anchor video demonstrates costovertebral angle tenderness — often shortened to CVA tenderness. The costovertebral angle is the corner low on your back where the lowest rib meets the spine, roughly over each kidney. During the examination, the clinician taps gently over that area. If the tapping hurts, that tenderness supports the suspicion that a kidney is inflamed. It takes just over a minute to watch, and it is one piece of the picture rather than a test on its own — your clinician combines it with your symptoms, your temperature, and urine testing.

What happens when you see a clinician?

Expect questions about your symptoms and temperature, that back examination, and a urine sample, which can be tested for signs of infection and sent to identify the bacteria involved. Blood tests are sometimes added, particularly if you feel very unwell. Treatment is with antibiotics, chosen by your clinician, and plenty of fluids are usually encouraged unless you've been told to limit them for another reason. Some people — for example if they're vomiting, very feverish, pregnant, or not improving — are assessed in hospital instead. Don't try to judge which group you're in by yourself; that assessment is part of the visit.

When should you seek help promptly?

Get medical help the same day if you have flank or back pain with fever, chills, nausea or vomiting, or urinary symptoms that are getting worse rather than better. Seek urgent help if you feel seriously unwell, can't keep fluids or medicine down, or notice you're passing very little urine. A kidney infection that's treated promptly usually settles well; one that's left can make you much sicker, which is why clinicians would always rather check early.

Frequently Asked Questions

Can a bladder infection turn into a kidney infection?
Yes. Bacteria that start in the bladder can travel up the tubes that connect the bladder to the kidneys. That's one reason urinary symptoms with new back pain and fever should be checked promptly rather than waited out.

Is kidney infection pain always in the back?
The classic pain is in the flank — the side of the back, under the lowest rib — which is why the examination in the video above taps over that area. Pain can also be felt lower in the abdomen, so the whole pattern of symptoms matters, not one sign alone.

Can I treat a kidney infection at home without seeing anyone?
No. A kidney infection needs assessment and prescription antibiotics chosen by a clinician. Rest and fluids can support recovery, but they aren't a substitute for being seen — especially if you have fever, vomiting, or worsening pain.

MedicalVideos.com has published trusted medical videos since 2007. The site was founded by Dr. Mohamed Ibrahim, MD, PhD — physician and researcher.

Educational only — this article is general information about kidney infection (pyelonephritis), not medical advice and not a diagnosis. If you think you may have a kidney infection, see a clinician promptly for assessment and treatment.