Why does kidney infection cause flank pain?

A kidney infection can cause flank pain because inflammation and swelling stretch the kidney and irritate nearby tissues in the side of the back. The kidneys sit toward the back of the upper abdomen, beneath the lower ribs, so discomfort is often felt there rather than directly over the bladder. Flank Pain is a very common presentation of Kidney Infection.

A urinary infection can sometimes travel upward from the bladder into a kidney. The resulting irritation may cause a deep ache, tenderness, or sharper pain on one side; it can also be felt on both sides. Fever, chills, nausea, burning when passing urine, needing to pass urine often, or urine that looks cloudy can occur alongside the pain. Flank pain also has other possible causes, including muscle strain or a urinary stone, so its location alone cannot identify the cause.

Arrange prompt medical assessment if flank pain occurs with urinary symptoms or feeling unwell. A clinician may check your temperature, examine the tender area, and test a urine sample to look for infection. Treatment may include antibiotics when a bacterial kidney infection is diagnosed; take them exactly as prescribed and complete the course unless the prescriber tells you otherwise. Drink fluids if you can keep them down, rest, and use only pain relief that is suitable for you and your medical history.

Seek urgent medical care for flank pain with a high fever, shaking chills, repeated vomiting, confusion, marked weakness, or difficulty passing urine. Get urgent advice as well if you are pregnant, have diabetes, a weakened immune system, known kidney disease, or a urinary catheter, because infection can be harder to manage in these situations. Worsening pain or an inability to drink enough fluid also needs timely assessment.

Ask whether your symptoms fit a kidney infection or whether another cause of flank pain needs checking. You can also ask what your urine test shows, which pain medicines are appropriate for you, and what change in symptoms should prompt urgent reassessment. Mention previous urinary infections, kidney stones, allergies to antibiotics, and any medicines you already take.