When your kidneys hurt, something is stretching or irritating the outer covering of the kidney, called the renal capsule. The kidneys themselves don’t have many pain-sensing nerves deep inside, but this outer shell does. Any condition that causes the kidney to swell rapidly, whether from a stone blocking urine flow, an infection, or a growing cyst, pulls on that capsule and sends pain signals to your brain. The sensation typically lands in your flank, the area on either side of your spine just below your ribs and above your hips.
How Kidney Pain Feels Different From Back Pain
Because the kidneys sit against the back muscles right below the rib cage, it’s easy to confuse kidney pain with a pulled muscle or spinal issue. A few key differences help you tell them apart. Kidney pain stays in one spot and doesn’t get worse or better when you shift positions, bend, or stretch. Muscular back pain, on the other hand, almost always changes with movement. You’ll feel it flare when you twist or lift, and it eases when you rest in certain positions.
Kidney pain also tends to radiate in specific directions. It can spread downward into the lower abdomen or inner thighs, whereas muscular pain usually stays along the spine or across the lower back. Another hallmark: kidney pain rarely improves on its own without some form of treatment, while a strained muscle will gradually feel better with rest and ice over a few days.
Kidney Stones: The Most Common Culprit
A kidney stone that stays put inside the kidney often causes no symptoms at all. The trouble starts when a stone drops into one of the ureters, the narrow tubes connecting each kidney to your bladder. If it gets stuck there, it blocks urine flow, the kidney swells, and the ureter spasms around the stone. That combination produces waves of intense, cramping pain that many people describe as the worst they’ve ever experienced.
The pain changes character as the stone moves through your urinary tract. It may start deep in your flank, then shift to your lower abdomen or groin as the stone travels downward. You might also notice blood in your urine, since the stone scrapes the lining of the ureter on its way through. Small stones often pass on their own with pain management and plenty of fluids, but larger stones or those that refuse to budge sometimes require a procedure to break them up or remove them. Size, location, and the type of stone all factor into the treatment plan.
Kidney Infections
A kidney infection, known medically as pyelonephritis, usually starts as a bladder infection that climbs upward. The infected kidney tissue swells, stretching that pain-sensitive outer capsule, and produces a steady, aching pain rather than the sharp waves of a stone. What sets an infection apart from other causes is the whole-body reaction: fever, chills, nausea, and a general feeling of being unwell that hits quickly. A lower urinary tract infection might cause burning when you pee, but a kidney infection is more likely to make you feel genuinely sick.
Kidney infections need prompt treatment with antibiotics. Left untreated, bacteria can spill into the bloodstream and cause a body-wide infection that becomes dangerous fast. If you have flank pain paired with a fever, that combination alone warrants medical attention.
Chronic Conditions That Cause Ongoing Pain
Not all kidney pain comes and goes in a dramatic episode. Polycystic kidney disease, a genetic condition where fluid-filled cysts grow on the kidneys, can cause a dull, persistent ache in the flank or abdomen that lasts for weeks or months. The pain is typically manageable with acetaminophen, and many people don’t need more than that. Ibuprofen and similar anti-inflammatory drugs are generally not recommended for people with this condition, especially when kidney function is already reduced.
Sudden, sharp pain in someone with polycystic kidney disease is a different story. It usually signals bleeding inside a cyst, an infected cyst, or a kidney stone (which people with this condition are more prone to). When a large cyst is causing severe, activity-limiting pain, doctors can drain it through the skin with a needle. Most people get significant relief from drainage, though pain can return, and some eventually need surgery for long-term management.
What You Might Notice in Your Urine
Your urine often provides the first visible clue that something is happening in your kidneys. Blood in the urine, which can look pink, red, or cola-colored, accompanies many of the conditions that cause kidney pain. Kidney stones, infections, and cysts can all produce it. In some cases, blood clots form and cause additional pain as they pass through the urinary tract or block urine flow.
Sometimes the blood is only detectable under a microscope, meaning your urine looks completely normal to you. That’s one reason a simple urine test is usually one of the first things ordered when you report kidney pain. Changes in how often you need to urinate, a persistent urgent feeling, or pain during urination are other signals worth paying attention to, even when your urine looks clear.
How Kidney Pain Gets Diagnosed
When you show up with flank pain, expect a urine sample and blood work. A urine test checks for blood, bacteria, and other signs of infection or stones. Blood tests measure how well your kidneys are filtering waste. One key number is your estimated glomerular filtration rate, or eGFR, which reflects your kidney’s filtering capacity. A normal eGFR falls between 90 and 120, though it naturally declines with age: the average for someone in their 60s is around 85, while for someone in their 20s it’s closer to 116. If your eGFR stays below 60 for three months, that meets the threshold for chronic kidney disease.
For imaging, a CT scan without contrast dye is the preferred first-line study when a stone is suspected. It’s highly sensitive and can pinpoint a stone’s size and exact location. Ultrasound is used instead for pregnant women and children, since it avoids radiation exposure. The imaging results, combined with your lab work and symptoms, usually make the cause clear.
Signs That Need Immediate Attention
Some combinations of symptoms point to a situation that can’t wait for a scheduled appointment. You should head to an emergency room if your kidney pain comes with any of the following:
- Inability to urinate, which may mean a complete blockage
- Fever or chills, suggesting infection that could spread
- Severe nausea or vomiting, especially if you can’t keep fluids down
- Blood in your urine
- Unmanageable pain that doesn’t respond to over-the-counter medication
- A sudden, repeated urgency to urinate that’s unusual for you
- Persistent low energy or feeling of illness that won’t resolve
A blocked kidney that can’t drain urine, or an infection spreading beyond the kidney, are both time-sensitive problems. The earlier they’re caught, the simpler the treatment and the lower the risk of lasting damage to kidney function.