A ureteral stone is a kidney stone that has moved out of the kidney and into one of the ureters, the narrow tubes that carry urine from each kidney down to the bladder. The stone itself forms in the kidney, but once it drops into a ureter, it can partially or fully block urine flow, causing intense pain that many people describe as the worst they’ve ever experienced. About 1 in 10 people will deal with a urinary stone at some point in their lives, and the ureter is where these stones cause the most trouble.
How a Ureteral Stone Forms
Stones don’t actually originate in the ureter. They start as small, hard mineral deposits in the kidney’s collecting area, called the renal pelvis. Most are made of calcium combined with oxalate or phosphate, though a smaller percentage are composed of uric acid or other compounds. While sitting in the kidney, stones often cause no symptoms at all. The problems begin when a stone gets flushed into the ureter by the normal flow of urine.
The ureters are only about 3 to 4 millimeters wide at their narrowest points. A stone that fit comfortably inside the kidney can suddenly become a tight squeeze. If the stone is small enough, it slides through and reaches the bladder within days or weeks. If it’s too large, it gets stuck, blocks urine from draining, and triggers the hallmark wave of pain known as ureteric colic.
What the Pain Feels Like
The classic symptom is a sudden, sharp, cramping pain that starts in your flank (the side of your back below the ribs) and radiates downward toward the groin. The pain comes in waves because the ureter is a muscular tube that contracts to try to push the stone along. Between waves, the pain may ease but rarely disappears entirely while the stone is still lodged.
Where exactly you feel the pain depends on where the stone is sitting in the ureter. A stone high in the ureter tends to cause back and flank pain. As it moves lower, the pain shifts toward the lower abdomen and groin. Other common symptoms include nausea, vomiting, blood in the urine (which may look pink or red), and a frequent urge to urinate, especially once the stone nears the bladder.
Stone Size and Your Odds of Passing It
Size is the single biggest factor in whether a ureteral stone will pass on its own. A large study tracking nearly 400 stones found clear thresholds:
- Under 3.5 mm: About 98% pass without intervention.
- 3.5 to 4.4 mm: Around 81% pass on their own.
- 4.5 to 5.4 mm: The odds drop to about 65%.
- 5.5 to 6.4 mm: Only about 33% pass spontaneously.
- 6.5 mm and larger: Fewer than 10% will pass without a procedure.
Small stones typically clear within one to two weeks. Larger ones can take much longer, and most stones above 6 mm will eventually need some form of treatment.
How a Ureteral Stone Is Diagnosed
If you show up with sudden flank pain, the first step is usually imaging. A non-contrast CT scan is the gold standard, with sensitivity as high as 97% for detecting stones anywhere in the urinary tract. It’s fast, doesn’t require any dye injection, and can also reveal whether the stone is causing a backup of urine in the kidney (called hydronephrosis).
Ultrasound is sometimes used as a first-line option, particularly in pregnant patients or when radiation exposure is a concern. However, it picks up ureteral stones only about 24% to 61% of the time, making it far less reliable than CT for stones lodged in the middle of the ureter. It’s better at detecting the indirect signs of obstruction, like a swollen kidney, than the stone itself.
Treatment for Smaller Stones
When the stone is 10 mm or smaller and there’s no sign of infection or complete blockage, the standard approach is to wait and let it pass. This isn’t purely passive, though. Medications that relax the smooth muscle lining the ureter can meaningfully improve your chances and speed things up. These drugs, originally developed for prostate conditions, widen the ureter slightly, giving the stone more room to travel.
A meta-analysis of 24 studies found that patients taking one of these medications had a 73% stone-free rate compared to 54% for those who didn’t. The medication also shortened the average passing time by roughly 3 to 4 days. The benefit is most pronounced for stones larger than 5 mm, where the extra dilation makes the biggest difference. During this waiting period, you’ll also be given pain medication and told to drink plenty of fluids to keep urine flowing.
When a Procedure Is Needed
Between one-fifth and one-third of ureteral stones ultimately require a procedure. The two main options are shock wave lithotripsy and ureteroscopy.
Shock wave lithotripsy uses focused sound waves delivered from outside the body to break the stone into smaller fragments that can then pass naturally. It’s noninvasive and usually done as an outpatient procedure, but it doesn’t always work on the first attempt. In a large randomized trial, about 22% of patients treated with shock wave lithotripsy needed additional treatment afterward.
Ureteroscopy involves passing a thin, flexible scope up through the bladder and into the ureter to reach the stone directly. The stone is either grabbed and removed or broken apart with a laser. It’s more invasive, but also more definitive. In the same trial, only about 10% of ureteroscopy patients needed further treatment. The trade-off is a slightly longer recovery and higher upfront cost. Overall, ureteroscopy was 11% more effective and associated with about 10 more healthy days over a six-month follow-up period.
Complications to Watch For
Most ureteral stones, even painful ones, resolve without serious harm. But a stone that completely blocks a ureter can create a dangerous backup. Urine trapped above the stone can become a breeding ground for bacteria, leading to a kidney infection that may progress to a bloodstream infection (sepsis). Warning signs include fever, chills, and worsening flank pain that doesn’t follow the usual wave pattern.
A blocked kidney also struggles to maintain normal blood chemistry. Potassium levels can rise because the kidney can’t excrete it properly, which in severe cases affects heart rhythm. These complications are uncommon but require urgent drainage of the blocked kidney, typically through a stent placed in the ureter or a tube inserted through the back directly into the kidney. Once the obstruction is relieved, the chemical imbalances usually correct themselves quickly.
Recurrence Is Common
One of the most important things to know about ureteral stones is that they tend to come back. The recurrence rate is as high as 50% within five years and 80 to 90% within ten years. That makes prevention a long-term concern, not just a one-time fix.
The simplest and most effective preventive measure is staying well hydrated, aiming for enough fluid to produce at least 2 to 2.5 liters of urine per day (roughly clear to pale yellow). Dietary changes depend on the type of stone you formed. For calcium oxalate stones, the most common type, reducing sodium and animal protein intake while maintaining adequate calcium from food (not supplements) can lower your risk. Your doctor may analyze a passed stone to determine its composition, which helps guide specific dietary or medication recommendations tailored to your situation.