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Published on: 7/15/2026

When should I be concerned about flank pain?

Flank pain requires medical attention when it occurs alongside fever, blood in the urine, severe or worsening pain, or interferes with daily activities. These warning signs may indicate a kidney infection, kidney stones, or another underlying condition that needs prompt evaluation.

Because flank pain has many possible causes—ranging from muscle strain to urinary tract issues—identifying the source quickly matters. Taking a free, instant, online symptom check can help you understand what may be causing your pain, gauge its urgency, and guide your next steps before seeing a doctor.

Reviewed for medical accuracy: 07/14/2026

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Explanation

Flank pain is the pain you feel in your side near your back. Sometimes it lasts for a short time and might be from a minor issue, but other times it can be a sign of something serious. You should be concerned and see a doctor if the pain is very strong or comes on suddenly. Also, if you notice other symptoms like a fever, chills, or if your urine looks unusual—maybe cloudy or even has blood in it—it might indicate an infection such as pyelonephritis. Other problems, like kidney stones, can also cause sharp pain that starts in the flank area and moves toward your lower belly or groin. Even in children, unusual causes like nutcracker syndrome (a condition that affects the kidney) have been mentioned. Keeping track of your pain and any other symptoms is important, and using a free AI symptom checker can help you understand what might be causing your discomfort and whether you should seek immediate medical attention.

(References)

  • Bueschen AJ. Flank Pain. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Boston: Butterworths; 1990. Chapter 182.

  • Agarwal A, Litra F, Barr LL. A Rare Cause of Abdominal and Flank Pain in Children: Nutcracker Syndrome. Cureus. 2021 Jul 16;13(7):e16422. doi: 10.7759/cureus.16422. PMID: 34414047; PMCID: PMC8364742.

  • Belyayeva M, Leslie SW, Jeong JM. Acute Pyelonephritis. [Updated 2024 Feb 28]. In: StatPearls [Internet].

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