What Is Renal Colic?

Renal colic is the name for a specific kind of pain — a severe, cramping pain that starts in your flank or lower back and often comes in waves. It happens when a stone or another blockage forms in the urinary tract and urine backs up behind it. The pain is not caused by the stone scraping its way through. It is caused by pressure building inside the kidney and ureter, which is why the pain can be intense even when the stone itself is small.

The word “colic” is a little misleading. In medicine, colic usually means pain that comes and goes because a hollow organ is squeezing. In renal colic, the pain often does shift and surge, but it can also settle into a steady, severe ache. Understanding what is actually happening inside the urinary tract explains why the pain behaves the way it does — and why it needs prompt medical attention rather than waiting it out.

What Is Renal Colic?

Renal colic is a medical symptom, not a disease on its own. It is the pain produced when the upper urinary tract — the kidney or the tube leading from it, called the ureter — becomes blocked or partially blocked, most often by a kidney stone.

When urine cannot drain freely, pressure rises behind the blockage. That pressure stretches the wall of the ureter and the capsule around the kidney. The stretching activates pain fibers, and the result is the sharp, gripping pain people describe as renal colic.

Kidney stones are the most common cause, but they are not the only one. Blood clots, tumors, and scarring can also block the ureter. In rare cases, a piece of tissue or a structural problem does the same thing. The pain pattern can be similar regardless of the cause, which is one reason imaging — not the pain alone — is what confirms the diagnosis.

What Does Renal Colic Feel Like?

The pain of renal colic is usually severe and hard to ignore. Many people describe it as the worst pain they have felt. It typically begins in the flank — the area between your lower ribs and your hip — or in the lower back.

From there, the pain often moves downward as the stone travels. It may shift toward the groin, the genital area, or the inner thigh. This moving pattern is one of the clues that points toward a stone rather than other causes of back pain.

The pain tends to come in waves that build and fade, though it can also stay constant. People often cannot find a comfortable position. They may pace, rock, or shift constantly, unlike the relief that lying still can bring with muscle-related back pain.

Other symptoms can appear alongside the pain:

• Nausea and vomiting
• Blood in the urine, which may look pink, red, or brown
• Needing to urinate more often or a burning feeling when you do
• Feeling like you cannot fully empty your bladder
• Sweating, restlessness, or a sense of agitation

Fever and chills are not typical of uncomplicated renal colic. When they appear with this kind of pain, they suggest an infection behind the blockage, which is a medical emergency.

Why Does a Blockage Cause So Much Pain?

The pain comes from pressure, not from the stone itself. This is a point many people miss. A small stone lodged high in the ureter can hurt more than a larger one that sits quietly in the kidney without blocking flow.

The ureter is a narrow muscular tube roughly the width of a thin straw. When a stone gets stuck, the muscle above it keeps squeezing to push urine forward. That squeezing against a fixed blockage raises the pressure inside the tube. The wall stretches, and nerves in the wall and the kidney capsule fire.

The kidney capsule — the tough outer covering of the kidney — is rich in pain-sensitive fibers. When the kidney swells from backed-up urine, the capsule stretches, which produces a deep, aching pain in the flank. This is why the pain can feel both cramping and constant at the same time.

If the blockage is not relieved, the pressure can eventually affect how well the kidney filters blood. A blocked kidney that stays blocked can lose function over time. That is why the timeline matters and why this is not a wait-and-see situation for everyone.

What Causes Renal Colic Besides Stones?

Kidney stones account for the large majority of cases. But other conditions can block the ureter and produce the same pain pattern.

Blood clots can form and travel into the ureter, especially in people with certain bleeding disorders or after trauma. Tumors in the kidney, ureter, or nearby structures can press on or grow into the urinary tract. Scar tissue from past surgery, radiation, or infection can narrow the ureter and slow the flow of urine.

Rarely, a condition called ureteropelvic junction obstruction — a narrowing where the kidney meets the ureter — causes urine to back up. Some people are born with it and do not notice until symptoms appear later in life.

Because these causes can look identical to a stone on symptoms alone, imaging is essential. A CT scan without contrast is often used because it can find stones, measure their size, and show the level of blockage. Ultrasound is often used first in certain situations, such as during pregnancy, when avoiding radiation matters.

How Is Renal Colic Diagnosed?

Diagnosis starts with the pattern of pain and a urine test. A urine sample can show blood, which is common with stones, or signs of infection, which changes the urgency of care.

Imaging confirms the cause and location. A non-contrast CT scan of the abdomen and pelvis is the most accurate test for stones in most adults. It shows the stone’s size, its position, and whether urine is backing up into the kidney.

Blood tests check kidney function and look for signs that the blockage is affecting how the kidneys are working. These results help guide how quickly treatment needs to move.

Size matters for what happens next. Small stones often pass on their own. Larger stones are less likely to pass without help. The exact size threshold where passing becomes unlikely varies, and clinicians weigh size along with location, symptoms, and the person’s overall health.

How Is Renal Colic Treated?

Treatment has two goals: relieve the pain and clear the blockage. Pain control usually comes first and often includes nonsteroidal anti-inflammatory drugs, which are commonly used for stone pain. Acetaminophen and, in some settings, stronger pain medications may also be used.

For stones that are likely to pass, clinicians often recommend drinking enough fluids and may prescribe a medication that relaxes the ureter to help the stone move. The evidence on how well these medications work is mixed, and some studies suggest the benefit is modest.

When a stone is too large to pass, or when there is infection, severe kidney impairment, or pain that cannot be controlled, a procedure is needed. Options include:

• Shock wave lithotripsy — sound waves break the stone into smaller pieces that can pass
• Ureteroscopy — a thin scope removes or breaks up the stone directly
• Percutaneous nephrolithotomy — surgery for large or complex stones
• Stent placement — a tube holds the ureter open to let urine drain

Which option is best depends on the stone’s size and location, the person’s anatomy, and whether infection is present. There is no single approach that fits everyone.

When Should You Get Medical Help?

Severe flank or back pain that comes with nausea, blood in the urine, or pain that will not let you sit still needs prompt medical attention. Do not try to manage it at home with pain relievers alone.

Some signs point to a true emergency. Get care immediately if you have:

• Fever or chills along with the pain
• Vomiting that will not stop
• Pain so severe you cannot function
• Very little urine output or none at all
• Confusion, weakness, or fainting

Fever with a blocked urinary tract is a serious combination. It can mean infection has spread behind the blockage, which can become life-threatening. This is not a situation to watch at home.

People with a single kidney, a kidney transplant, or known kidney disease should seek care early. A blockage in these situations carries higher risk.

Can Renal Colic Be Prevented?

Prevention depends on why the stones formed. Most kidney stones are made of calcium oxalate, and several factors raise the risk, including not drinking enough water, eating a lot of sodium, and having certain medical conditions.

Drinking more water is the most widely recommended step. More urine means less concentrated urine, which makes it harder for crystals to form and grow into stones. The exact amount that helps varies by person, and clinicians often suggest aiming for enough fluid to produce pale urine throughout the day.

Diet changes can help some people. Reducing sodium intake and getting calcium from food rather than avoiding it are common recommendations, because calcium in food can bind oxalate in the gut before it reaches the kidneys. Cutting calcium entirely is generally not advised and can sometimes raise stone risk.

For people who form stones repeatedly, a doctor may check urine and blood chemistry to find the specific cause. Depending on the results, medications may be prescribed to change the chemistry of the urine. This is tailored to the individual, not a one-size-fits-all plan.

Anyone who has had one stone is at higher risk of another. That makes follow-up care and prevention worth taking seriously, even after the pain has passed.