Symptoms & Causes of Kidney Pain

Kidney pain is typically felt deep in the flank, the area beneath the lower ribs on either side of the spine. While usually caused by benign conditions like kidney stones or infections, persistent flank pain warrants a medical evaluation to rule out underlying issues, including kidney cancer. Because early kidney tumors may not cause noticeable symptoms, many are discovered incidentally during diagnostic imaging performed for unrelated reasons.

What Are the Symptoms of Kidney Pain?

Because the kidneys sit deep within the retroperitoneum, identifying true kidney pain involves recognizing the specific quality of the discomfort alongside accompanying urinary or systemic warning signs.

Possible symptoms associated with kidney pain include:

• Flank or side pain: A deep, persistent ache beneath the lower ribs on one or both sides of the back. Kidney-related pain may be less affected by movement or position than musculoskeletal pain, although the patterns can overlap.
• Blood in the urine (hematuria): Urine that appears pink, red, or cola-colored, or microscopic blood detected during a urinalysis.
• Changes in urination: Pain or burning during urination, increased frequency, urgency, or difficulty passing urine, which often indicate an infection or blockage.
• Fever, chills, nausea, or vomiting: These symptoms may occur with a kidney infection and are especially concerning when accompanied by flank pain, painful urination, or other urinary changes.
• Fatigue, loss of appetite, or unexplained weight loss: Broader systemic signs that can accompany chronic renal issues or advanced kidney tumors.
• A lump or swelling in the side: A noticeable abdominal or flank mass, which is uncommon in early disease but may develop as a tumor expands.

What Causes Kidney Pain?

Kidney pain develops when the tissues of the kidney or surrounding urinary structures become infected, inflamed, physically blocked, or stretched. Determining the underlying cause requires evaluating the specific nature of the discomfort alongside accompanying symptoms.

Benign & Inflammatory Conditions

The vast majority of flank pain stems from non-cancerous conditions. Kidney stones cause sharp, severe, intermittent pain (renal colic) when a mineral deposit moves into or blocks the ureter. Kidney infections (pyelonephritis) develop when bacteria ascend from the bladder into the kidney tissue, causing localized flank tenderness alongside fever and nausea. Additionally, polycystic kidney disease, large or complicated simple cysts, and urinary tract blockages such as hydronephrosis can create pressure within or around the kidney and contribute to flank discomfort.

Renal Masses & Vascular Issues

Kidney cancer (renal cell carcinoma) originates in the kidney's filtering tubules. While early tumors are typically small and asymptomatic, an expanding mass can stretch the fibrous renal capsule or invade surrounding retroperitoneal nerves, producing a persistent flank ache. Less common causes include renal vein thrombosis (blood clots in kidney vessels) or direct physical trauma from falls, accidents, or contact sports.

#1 Cancer Hospital in Tampa

Ranked as Tampa's #1 Cancer Hospital in U.S. News & World Report's list of America's Best Hospitals for Cancer Care.

Schedule an Appointment

How Is Kidney Pain Evaluated?

When evaluating flank pain, a physician will review your medical history, ask when the discomfort began, assess whether it changes with body movement, and check for accompanying urinary or systemic symptoms.

Initial diagnostic testing typically includes a urinalysis and urine culture to check for microscopic blood, white blood cells, or active bacterial infections. Your doctor may also order blood tests to evaluate kidney function (creatinine and BUN) alongside high-resolution diagnostic imaging, such as an ultrasound, non-contrast CT scan, or MRI, to visualize kidney stones, urinary obstructions, fluid-filled cysts, or solid renal masses.

When Is Kidney Pain an Emergency?

Not every episode of flank pain requires emergency treatment. However, persistent or unexplained pain should be evaluated, and severe pain or certain accompanying symptoms may indicate a kidney infection, urinary blockage, bleeding, or another condition requiring immediate care.

You should seek immediate emergency medical evaluation if your kidney pain is accompanied by any of the following warning signs:

• A sudden, high fever accompanied by shaking chills
• Inability to keep fluids down due to persistent nausea and vomiting
• Visible blood or blood clots in your urine
• Sudden inability to pass urine
• Extreme, unbearable pain that comes on rapidly and prevents you from standing or sitting comfortably

Related Topics & Patient Resources

If you are trying to determine whether your symptoms are coming from your back muscles or your kidneys, explore our dedicated patient guide:

• What Is the Difference Between Lower Back Pain and Kidney Pain? – Learn how location, body movement, and accompanying systemic symptoms help differentiate kidney pain from typical muscular lower back pain.

Comprehensive Kidney Pain Diagnostic Evaluation at Moffitt Cancer Center

While the majority of kidney pain cases stem from benign conditions like kidney stones or bacterial infections, persistent flank pain or unexplained blood in the urine should always be evaluated by a urologic specialist to rule out underlying malignancies.

At Moffitt Cancer Center, our Urologic Oncology Program utilizes advanced diagnostic testing, including high-resolution CT urography, MRI, ultrasound, and specialized urinalysis, to rapidly isolate the cause of kidney symptoms. Once an accurate diagnosis is established, our multidisciplinary team coordinates a personalized treatment strategy designed to alleviate pain and protect overall renal function.

If you’d like to discuss your kidney pain with a urologic oncologist at Moffitt Cancer Center, call 1-888-663-3488 or complete a new patient registration form online to request an appointment. We do not require referrals.