If a kidney stone won’t pass on its own, the pressure it creates can damage your kidney, raise the risk of serious infection, and cause escalating pain. Most stones under 5 mm pass naturally, with success rates around 76% to 100%. But stones between 5 and 10 mm drop to a passage rate of roughly 60% to 68%, and larger stones rarely make it out without help. When a stone gets stuck, the clock starts ticking on potential complications, and there are several well-established procedures to deal with it.
Why Some Stones Get Stuck
The ureter, the narrow tube connecting each kidney to the bladder, is only about 3 to 4 mm wide at its tightest points. A stone that’s small and smooth may slide through with nothing more than a few days of discomfort. A larger, jagged, or oddly shaped stone can lodge in place, partially or fully blocking urine flow. The most common sticking points are where the ureter meets the kidney, where it crosses over the pelvic bone, and where it enters the bladder.
Stone composition matters too. Calcium oxalate stones tend to have rough, spiky surfaces that grip the ureter wall, while uric acid stones are generally smoother. Location also plays a role in whether medication can help. Alpha-blocker medications relax the smooth muscle in the lower ureter and can increase the likelihood of passing a distal (lower) stone by about 52%. For stones lodged higher up near the kidney, these medications show no significant benefit, because the lower ureter has a much higher concentration of the receptors these drugs target.
The Waiting Window
When a stone is small enough that it might still pass, doctors typically allow 4 to 6 weeks of “watchful waiting,” often combined with pain management and plenty of fluids. During this window, you’ll usually have follow-up imaging to confirm the stone is moving and not causing worsening obstruction.
That timeline isn’t arbitrary. Animal studies show that relieving a ureteral obstruction within two weeks significantly reduces the chance of lasting kidney damage. Beyond two weeks of complete blockage, the probability of permanent harm rises sharply. In rat models, irreversible damage begins after just 72 hours of total obstruction, though human kidneys are more resilient and partial obstruction is more common than complete blockage. Still, the general principle holds: the longer urine backs up, the greater the risk.
What Happens to Your Kidney
When a stone blocks the ureter, urine pools behind it. That backed-up urine swells the kidney, a condition called hydronephrosis. In the short term, this causes the intense flank pain most people associate with kidney stones. But the real danger is what’s happening inside the kidney tissue.
The rising pressure compresses the tiny filtering units of the kidney, reducing blood flow and starving tissue of oxygen. Over time, this triggers inflammation and scarring (fibrosis) within the kidney. The filtering rate drops. If the obstruction continues, you can lose functioning kidney cells permanently. Prolonged blockage leads to cortical thinning, loss of filtering units, and structural changes that don’t reverse even after the stone is removed. In the worst case, a chronically obstructed kidney can lose so much function that it contributes to chronic kidney disease.
Acute obstruction, the kind that causes sudden severe pain, is actually more likely to be reversible than a slow, painless blockage that goes unnoticed for months. Silent obstruction is particularly dangerous because there’s no alarm bell prompting you to seek treatment.
Infection: The Most Dangerous Complication
A blocked kidney is a breeding ground for bacteria. Urine that can’t drain becomes stagnant, and any bacteria present multiply rapidly in that warm, trapped fluid. This can progress from a urinary tract infection to an infected, swollen kidney (pyonephrosis) and then to urosepsis, a life-threatening bloodstream infection.
Urosepsis is most commonly triggered by obstruction of the upper urinary tract, and kidney stones are the leading cause. In one study, more than half of patients with urosepsis had hydronephrosis. The combination of a blocked ureter, fever, and chills is treated as a medical emergency. In this situation, doctors prioritize draining the kidney immediately, sometimes by placing a thin tube through the back directly into the kidney, before even addressing the stone itself.
Warning signs that suggest infection alongside a stuck stone include fever, chills, cloudy or foul-smelling urine, nausea and vomiting, or an inability to urinate at all. If you develop a fever while dealing with a known kidney stone, that changes the situation from urgent to emergent.
Shock Wave Lithotripsy
When a stone won’t pass but is still relatively small, shock wave lithotripsy (SWL) is often the first procedure considered. You lie on a table while a machine sends focused sound waves through your body to break the stone into smaller fragments that can then pass naturally. It’s done under sedation, requires no incisions, and you typically go home the same day.
SWL works best for stones under 2 cm that are located in the kidney or upper ureter. For stones 10 mm or smaller in the ureter, single-treatment success rates range from about 66% to 75% depending on location. Stones in the lower part of the kidney are trickier because fragments tend to settle back into that pocket rather than draining out, with success rates dropping to 34% to 78% for stones between 10 and 20 mm in that location. Stones larger than 2 cm generally need a more hands-on approach.
Recovery from SWL is relatively quick. You may see blood in your urine for a day or two and feel bruising where the waves entered. The broken fragments pass over the following days to weeks, which can cause some discomfort but is far more manageable than passing the original stone.
Ureteroscopy and Laser Treatment
For stones stuck in the ureter, or those that SWL can’t handle, ureteroscopy is the go-to option. A thin, flexible scope is passed through the urethra, up through the bladder, and into the ureter to reach the stone directly. Once the scope is in position, a laser fiber breaks the stone into tiny fragments or dust that either washes out or gets extracted with a small basket tool.
Success rates for ureteroscopy are high. Studies report overall stone-free rates around 97%, with the best results for stones in the lower ureter (99%) and slightly lower rates for stones higher up near the kidney (92%). After the procedure, about half of patients receive a temporary internal stent, a small flexible tube left in the ureter to keep it open while swelling subsides. Stents can cause bladder irritation and a frequent urge to urinate, but they’re typically removed within a couple of weeks.
Surgery for Large or Complex Stones
Stones larger than 2 cm, or staghorn stones that fill much of the kidney’s internal space, usually require percutaneous nephrolithotomy (PCNL). This involves making a small incision in the back and passing instruments directly into the kidney to break up and remove the stone. It’s more invasive than the other options and requires general anesthesia and a hospital stay, typically one to two days. But for large stones, it has the highest success rate and clears the stone more completely in a single session than SWL or ureteroscopy can.
Recovery takes longer, usually one to two weeks before returning to normal activities, and carries higher risks of bleeding or infection compared to less invasive procedures. It’s reserved for situations where smaller tools simply can’t do the job.
What Recovery Looks Like
After any stone procedure, you’ll likely pass small fragments or grit for several days. Drinking extra water helps flush these out. Most people return to their normal routine within a few days after SWL or ureteroscopy, and within one to two weeks after PCNL. Follow-up imaging, usually an ultrasound or CT scan, confirms whether the stone has been fully cleared.
Having one kidney stone significantly raises your odds of getting another. Roughly half of people who pass a stone will develop a second one within five to ten years. Your doctor may analyze the stone’s composition if it’s captured and recommend dietary changes, increased fluid intake, or medication to reduce the chance of recurrence. Collecting the stone fragments in a strainer when you urinate is worth the effort, because knowing what the stone is made of shapes the prevention strategy.