Flank Pain

Overview

Flank pain is discomfort felt in the flank, the area on either side of the body between the bottom of the rib cage and the top of the hip, toward the back. It can be sharp, dull, cramping, or come in waves, and it may stay in one spot or spread toward the groin, lower abdomen, or back. Flank pain can affect one side or both.

Because the kidneys sit in this region, flank pain is often linked to kidney and urinary problems, but it can also come from muscles, the spine and nerves, or organs in the abdomen. The character of the pain, what makes it better or worse, and the symptoms that go with it all help point to the cause. A steady ache that worsens with movement often comes from muscles, while pain that builds in intense waves frequently signals a kidney stone. Severe flank pain, especially with fever or blood in the urine, needs prompt medical attention, as it can reflect a kidney infection or a blocked urinary tract that requires timely treatment.

Common Causes

Flank pain has many possible sources, ranging from muscle strain to urinary tract problems.

• Kidney stones: A classic cause of severe, cramping flank pain that comes in waves and may radiate to the groin, often with blood in the urine.
• Kidney infection (pyelonephritis): Infection of the kidney causing flank pain, fever, chills, and painful urination.
• Urinary tract infection: Lower tract infections can sometimes cause side discomfort.
• Muscle strain: Overuse or injury of the back and side muscles.
• Spine and nerve problems: A pinched nerve, shingles, or arthritis of the spine can cause flank pain.
• Other organ causes: Problems with the gallbladder, pancreas, or, less often, the abdominal aorta can be felt in the flank.

Associated Symptoms

The symptoms that accompany flank pain help narrow down the cause and reveal how urgent it is.

• Blood in the urine or pink, red, or cola-colored urine
• Painful, frequent, or urgent urination
• Fever, chills, or feeling generally unwell
• Nausea and vomiting, common with kidney stones
• Pain that spreads to the lower abdomen or groin
• A rash or blistering on one side of the body (suggesting shingles)
• Pain that worsens with movement or pressing on the muscles (suggesting a muscle or spine cause)

Fever with flank pain raises concern for a kidney infection, which needs prompt treatment.

Diagnosis & Evaluation

A clinician evaluates flank pain by asking about its onset, character, and associated symptoms, then examining the back, abdomen, and side. Tests depend on the suspected cause.

• Urine tests: Check for blood, infection, or crystals that suggest stones.
• Blood tests: Assess kidney function and signs of infection.
• Imaging: Ultrasound or CT scans can detect kidney stones, infection, blockage, or other abdominal problems.
• Examination of the spine and muscles: Tenderness that worsens with movement points to a musculoskeletal cause.

If the pain is mild and clearly muscular, extensive testing may not be needed, but persistent, severe, or feverish flank pain warrants thorough evaluation.

Treatment & Management

Treatment is directed at the underlying cause, with relief of pain along the way.

• Kidney stones: Small stones often pass with fluids and pain relief; larger or stuck stones may need procedures to break up or remove them.
• Kidney infection: Treated with antibiotics, sometimes in the hospital if severe.
• Muscle strain: Rest, gentle stretching, heat or cold, and over-the-counter pain relievers usually help.
• Nerve causes: Shingles is treated with antiviral medicine, and nerve-related back pain is managed accordingly.

Staying well hydrated supports kidney health and can help prevent some stones. Never ignore severe or feverish flank pain while waiting for it to pass.

When to See a Doctor

See a doctor promptly for flank pain that is severe, persistent, or comes with worrying features. Seek urgent or emergency care if you have:

• Severe, unrelenting flank pain, especially in waves
• Fever and chills with flank pain
• Blood in the urine
• Nausea and vomiting that prevent keeping fluids down
• Inability to urinate or a sudden drop in urine output
• Fainting, a racing heart, or sudden severe back and abdominal pain (which can signal a serious blood vessel problem)

Related Topics

Frequently Asked Questions

References

1. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Kidney Stones.
2. Mayo Clinic. Kidney infection — Symptoms and causes.
3. MedlinePlus, U.S. National Library of Medicine. Flank pain.
4. Centers for Disease Control and Prevention (CDC). Urinary tract infections.