Sudden flank pain: what to know

The flank is the area between the ribs and hip on either side of the back. Pain that follows lifting, twisting or movement may come from muscles. Kidney stones can cause intense, wave-like pain that may travel towards the groin, with nausea or blood in the urine. Kidney infection may cause flank or back pain with fever, chills, painful urination or feeling unwell. A urinary tract infection can cause burning or frequent urination, although it may not explain severe flank pain by itself. Other abdominal, spinal or skin problems can feel similar.

Note which side hurts, whether pain is constant or comes in waves, what movement does to it, and any urinary, digestive, genital or pregnancy-related symptoms.

Rest in a comfortable position and avoid lifting until the cause is clearer. Drink normally unless a clinician has given you fluid restrictions; forcing large amounts of fluid will not reliably move a stone and may worsen nausea. Use only pain relief that is safe for you and follow label directions. Arrange prompt assessment for new severe pain, pain that is not settling, urinary changes, vomiting or fever. A clinician may need an examination, urine testing or imaging.

Seek emergency care for flank pain with fever and shaking chills, confusion, fainting, repeated vomiting, inability to pass urine, severe weakness or a single functioning kidney. Get urgent advice for blood in urine, severe pain that comes in waves, pregnancy, recent injury or pain with a new rash. Do not wait for home treatment to work if you feel rapidly worse.

Ask whether the pain pattern suggests a stone, infection or muscle problem, whether urine testing or imaging is needed, which pain medicines fit your health history, and which changes should bring you back urgently. Mention previous stones, urinary infections, pregnancy possibility, fever, medicines and fluid restrictions.