Flank pain

Category: Urinary & Kidneys · All urinary symptoms

What it can feel like

Flank pain is pain in the side of the body, between the ribs and the hip, often felt in the back on one side. Pain here is classically linked to the kidney — the colicky, wave-like agony of a kidney stone is one of the most severe pains described, typically with restlessness and nausea.

Possible causes

A symptom can have many causes, and most are not serious. The lists below group conditions this symptom can be associated with — common causes first. They are possibilities to discuss with a clinician, not a diagnosis.

Common causes

Flank pain can be associated with muscle strain of the back, kidney infection (usually with fever and urinary symptoms), and shingles before the rash appears on that side.

Other possible causes

Flank pain can also be associated with kidney stones blocking the urine flow, bleeding into the kidney, a blocked or infected kidney (which is an emergency combination), and problems of nearby organs such as the gallbladder, pancreas or lung base.

Red flags — when to seek help promptly

Flank pain with fever or shivering — an infected, obstructed kidney is an emergency
Severe waves of pain travelling to the groin, with vomiting
Flank pain with blood in the urine or inability to pass urine
Flank pain in pregnancy, or in someone with only one kidney

What a clinician may do

A clinician will check temperature and pulse, test urine for blood and infection, and take blood tests for kidney function and inflammation. A CT scan is the usual way to confirm a stone; ultrasound is used first in pregnancy and in children. An infected, blocked kidney needs urgent drainage and antibiotics.

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Frequently asked questions

How is kidney stone pain different from back pain?

Stone pain (renal colic) comes in waves, is often severe enough to make people pace rather than lie still, and travels from the flank around to the groin. Back strain is more positional and eases with rest and position change.

Why is pain plus fever so dangerous here?

A stone that blocks the kidney while infection is present traps infected urine under pressure, which can rapidly enter the bloodstream (sepsis). That combination needs emergency drainage — with a stent or a tube into the kidney — alongside antibiotics.

Related symptoms — Urinary & Kidneys

Being unable to pass urine Blood in the urine Cloudy or strong-smelling urine Difficulty starting to urinate Foamy urine Leaking urine (incontinence)

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Please note: This page is educational information about a symptom. A symptom alone cannot diagnose any condition, and the causes listed here are possibilities, not a diagnosis. If you are worried about a symptom — especially one that is new, severe, getting worse or not going away — please see your own clinician, who can examine you and arrange tests. In an emergency, call your local emergency number.