What should you know about severe left flank pain?

Flank pain is felt between the ribs and hip, often toward the side or back. Kidney stones can cause intense waves of pain that may move toward the groin, while a kidney infection may cause flank pain with fever, chills, nausea or painful urination. A urinary tract infection can involve urinary burning, urgency or cloudy urine. Muscle strain, bowel problems and other conditions can feel similar, so location alone cannot identify the cause.

Stop strenuous activity and note when the pain began, whether it comes in waves, and any urinary or digestive changes. Sip fluids if you can keep them down, but do not force large amounts if vomiting or if a clinician has advised fluid restriction. Use only pain relief that is safe for you and follow the label. Do not use leftover antibiotics; the right treatment depends on examination and testing.

Seek urgent care for severe or worsening pain, fever with flank pain, repeated vomiting, faintness, confusion, inability to pass urine, blood in urine, or pain during pregnancy. Immediate assessment is also needed if you have one kidney, significant immune suppression or feel suddenly very unwell. These features can signal infection, obstruction or another emergency.

Tell the clinician about the pain’s exact position, timing, movement and severity, plus fever, urine changes, bowel symptoms and medicines. Ask whether a urine test, blood test or imaging is appropriate, what diagnosis is being considered, and which warning signs should bring you back.