Diarrhea and Flank Pain: What Should You Know?

Flank pain is felt between the ribs and hips, usually on one side of the back or body. Diarrhea can cause cramping and loss of fluid, while pain in the flank may point to the urinary tract, kidneys, muscles, or another nearby organ. The two symptoms can happen at the same time without having the same cause.

A short-lived infection affecting the digestive system can cause loose stools, abdominal cramps, nausea, and general body aches. Repeated stools can leave you dehydrated, which may cause weakness, dizziness, headache, or muscle aching that is felt near the flank.

Flank pain that is strong, comes in waves, or spreads toward the groin can occur with a kidney stone. Pain with burning urination, an urgent need to urinate, cloudy or strong-smelling urine, or fever can occur with a urinary tract infection or kidney infection. Diarrhea does not by itself identify any of these conditions. A clinician may need to assess the pain pattern, hydration, abdomen, and urine.

Take frequent small sips of water or an oral rehydration drink. If nausea makes drinking difficult, try a sip every few minutes. Eat light foods when you feel able, such as rice, toast, bananas, soup, or other foods you normally tolerate. Avoid alcohol and consider limiting greasy foods until your stomach settles.

Rest and monitor urine output, thirst, dizziness, fever, stool changes, and whether the flank pain is improving. Do not take leftover antibiotics. Ask a pharmacist or clinician before using an anti-diarrhea medicine if you have fever, blood or black stool, severe pain, or a significant medical condition. If the pain is clearly triggered by movement, gentle rest may help, but worsening or persistent pain needs assessment.

Seek urgent medical help for severe or rapidly worsening flank or abdominal pain, fainting, confusion, inability to keep fluids down, very little or no urine, blood in the stool or urine, black stool, or a high fever with chills. These features can signal significant dehydration, bleeding, a blocked urinary tract, or an infection requiring prompt treatment.

Arrange a medical review if diarrhea is not settling, keeps returning, or occurs with urinary burning, frequent urination, vomiting, fever, or pain that remains on one side. Get advice sooner if you are pregnant, older, immunocompromised, or have kidney disease, diabetes, or another condition that increases the impact of fluid loss. A clinician can decide whether urine testing, blood tests, or other evaluation is appropriate.

Ask: Could the flank pain be related to dehydration, a urinary infection, a kidney stone, or another cause? Do I need a urine test? Which fluids and foods are suitable for me? Is an anti-diarrhea medicine safe with my symptoms and medicines? What changes should prompt urgent help?