Left flank kidney pain: what to know

The flank is the area between the ribs and hip on the side of the back. Kidney stones may cause severe, wave-like pain that travels towards the groin, sometimes with nausea or blood in urine. A kidney infection may cause steadier flank pain with fever, chills, cloudy urine or painful urination. A urinary tract infection can cause burning and frequent urination, though flank pain suggests the infection may involve higher parts of the tract.

Muscle strain, shingles, bowel problems and other conditions can also cause pain in this region. Pain that changes with movement or pressing the area may have a musculoskeletal source, but this clue is not enough to diagnose it.

Arrange medical advice for new, persistent or recurrent flank pain, especially when urinary symptoms, fever or vomiting are present. A clinician may examine your abdomen and back, check urine, and decide whether blood tests or imaging are appropriate. Note when the pain began, whether it comes in waves, where it travels, and any urine or bowel changes.

Use only pain relief that is suitable for you and follow the label or clinician’s instructions. Do not delay review by assuming that one-sided pain is a stone or a pulled muscle.

Seek urgent care for flank pain with fever or chills, repeated vomiting, confusion, fainting, inability to pass urine, severe worsening pain, or feeling profoundly unwell. Pregnancy, a single functioning kidney, or known urinary blockage also lowers the threshold for prompt assessment.

Ask: Could this be a stone, infection or a non-urinary problem? Do I need a urine test or imaging? How should I manage pain safely? What changes in urine, temperature or pain mean I should seek emergency care?