What Is a Kidney Stent and When Is One Needed?

A kidney stent, more precisely called a ureteral stent, is a thin, flexible tube placed inside the ureter to keep urine flowing from the kidney to the bladder when something blocks or narrows that pathway. The most common design has a small curl at each end, earning it the nickname “double-J” or “pigtail” stent, because one curl anchors in the kidney and the other sits in the bladder. These stents are used across a wide range of situations, from draining a kidney backed up by a stone to keeping the ureter open during cancer treatment, and understanding what they do, how they feel, and when they come out can make the whole experience considerably less stressful.

How the Stent Actually Works

Your ureters are narrow muscular tubes, roughly the diameter of a pencil, that shuttle urine downward from each kidney to the bladder through rhythmic squeezing called peristalsis. When a stone, tumor, scar tissue, or swelling blocks a ureter, urine backs up into the kidney. That backup, called hydronephrosis, causes pain and can damage the kidney if it persists. A ureteral stent holds the ureter open and provides a channel for urine to flow past the obstruction, relieving pressure almost immediately.

The double-J design, which has been in clinical use for roughly four decades, uses the curled ends to prevent the tube from migrating up into the kidney or slipping down into the bladder.¹ Most stents are made from polyurethane or silicone polymers, though metallic versions exist for cases that need longer-term drainage.² Urine passes both through the hollow center of the tube and along small channels between the stent and the ureteral wall.

When a Stent Is Needed for Kidney Stones

The most common reason you might end up with a ureteral stent is a kidney stone that has lodged in the ureter and caused an obstruction, especially if the blockage triggers infection or severe pain that does not respond to medication. In that scenario, a stent is placed on an emergency basis to drain the kidney and buy time until the stone can be dealt with definitively.

A study tracking 196 patients who received emergency stents for obstructing stones found that roughly 42% of them were stone-free by the time the stent was removed, meaning the stone had passed on its own while the stent was in place. The remaining 58% still needed a procedure to extract the stone. Stone size and density were the strongest predictors of whether a second procedure would be necessary.³ In other words, a stent is sometimes a bridge to surgery and sometimes a standalone fix, depending largely on what kind of stone you have.

Stents After Ureteroscopy and Other Procedures

If you undergo ureteroscopy, a procedure where a scope is passed up through the bladder and ureter to laser or grab a stone, your surgeon will often place a stent afterward. The rationale is that the ureter swells from the instrumentation, and without a stent, that swelling could block urine flow in the days following surgery. A European survey of urologists found that in complicated cases, about three-quarters of respondents said they always place a stent after ureteroscopy.⁴ Common reasons cited included ureteral trauma during the procedure, a large stone burden, residual fragments, and having a solitary kidney.

That said, stenting after an uncomplicated ureteroscopy is not always necessary. A randomized multicenter trial compared stent placement with stent omission after ureteroscopy for kidney stones and found no difference in 30-day complication rates between the two groups (8% versus 11%). Patients who skipped the stent reported better quality-of-life scores in the short term.⁵ The takeaway is that routine stenting is not mandatory in straightforward cases, though many surgeons still default to it because the consequences of post-operative swelling in a stent-free patient can be severe.

Cancer and Malignant Obstruction

Tumors in the pelvis, abdomen, or urinary tract can compress or invade the ureter from the outside, blocking urine drainage. This is called malignant extrinsic ureteral obstruction, and stenting is one of two main ways to relieve it (the other being a nephrostomy tube placed through the back directly into the kidney). Stents in this setting serve a palliative role: they preserve kidney function and reduce pain while the cancer is treated, but they face higher failure rates than stents placed for stones.

One study found that stent failure occurred in about 19% of ureters with malignant obstruction, with a median time to failure of 63 days. Bladder invasion by the tumor and severe hydronephrosis before stent placement were the strongest predictors of failure. Patients without either risk factor had a three-month failure-free rate above 94%, while those with both risk factors dropped to about 56%.⁶ Factors like a long stretch of ureteral obstruction (over 3 cm), direct tumor invasion of the ureter, and a history of pelvic radiation also increase the risk that retrograde stent placement will fail altogether.⁷

In patients with advanced cancer, the decision to place a stent involves weighing kidney preservation against quality of life. Median survival after the first stent placement for malignant obstruction was reported at 266 days in one cohort, but roughly three-quarters of those patients died during follow-up, with a median time from stent insertion to death of 160 days.⁸ Risk-stratification models are being developed to help clinicians identify which patients will genuinely benefit from stenting versus those for whom the added procedures may not improve remaining quality of life.

Pregnancy and Symptomatic Hydronephrosis

Some degree of kidney swelling during pregnancy is normal, caused by hormonal changes and the growing uterus pressing on the ureters. Most cases resolve on their own. But in a minority of pregnant patients, the obstruction causes persistent pain, recurrent infections, or threatens kidney function. When conservative measures fail, a ureteral stent is one of two interventional options, the other being a nephrostomy tube.⁹

A retrospective study comparing stent placement with conservative treatment in symptomatic pregnant patients found that stenting did not significantly improve kidney function or obstetric outcomes overall, though it did provide symptom relief in select patients with persistent or severe discomfort.¹⁰ Stenting during pregnancy usually means exchanging the stent every four to six weeks until delivery, because the warm, mineral-rich urine of pregnancy accelerates encrustation.

How Stents Are Placed

Stent placement is almost always done under anesthesia, either general or sedation, and usually takes less than half an hour. The standard approach is retrograde: a cystoscope is inserted through the urethra into the bladder, the surgeon identifies the ureteral opening, and a guidewire is threaded up into the kidney. The stent slides over the wire, and its position is confirmed using fluoroscopy (real-time X-ray). Once the upper curl is seated in the kidney, the wire is removed and the lower curl springs into the bladder.¹¹

When retrograde placement is not possible, as sometimes happens with complete tumor obstruction, a nephrostomy tube is placed through the skin into the kidney, and a stent may be threaded antegrade (from the kidney down). Either way, you will typically have a follow-up X-ray or ultrasound to confirm the stent is in the right position.

Removal and the String Option

The traditional way to remove a ureteral stent is a brief cystoscopy, where a scope is passed through the urethra, the lower curl is grasped, and the stent is pulled out. This usually takes only a few minutes but requires a visit to the clinic or outpatient suite and can be uncomfortable, particularly for men.

An increasingly popular alternative is a stent with an extraction string: a thread attached to the lower end of the stent that exits through the urethra and is taped to the skin. When it is time for the stent to come out, the patient or a healthcare worker simply pulls the string. One study comparing string removal with cystoscopic removal found that men who had the string experienced significantly less pain, while women’s pain scores were similar between the two methods.¹² String-based stents also stayed in place for a shorter period on average, about 10 days compared with roughly 27 days for stents removed by cystoscopy, which matters because symptom severity increases with dwell time.¹³ Infection rates did not differ between the groups.

Despite these advantages, extraction strings are not used universally. Some surgeons worry about accidental early dislodgement, and patients sometimes find the string itself irritating. A prospective study investigating routine string use found it was safe and saved significant costs by eliminating cystoscopy visits.¹⁴

Living With a Stent

Few patients find a ureteral stent comfortable. The most common complaints are a frequent, urgent need to urinate, a burning or stinging sensation during urination, blood in the urine, and flank pain that may worsen with activity or a full bladder. Some people also experience pain that radiates to the groin or genital area when urinating, because the lower curl of the stent sits in the bladder and irritates its lining.

In-depth interviews with patients after ureteroscopy found that stent experiences fell into three broad groups: about a third described minimal impact on daily life, roughly half had moderate effects where some activities were affected and others were not, and about one in five experienced substantial disruption to sleep, mood, work, exercise, and social life.¹⁵ Psychological effects like anxiety and frustration came up repeatedly, even among patients whose physical symptoms were manageable.

Medications can help. A meta-analysis found that alpha-blocker drugs, a class typically used for prostate or blood-pressure conditions, were effective at reducing stent-related urinary symptoms and pain scores.¹⁶ Anticholinergic medications that calm bladder spasms have also been studied. A systematic review of solifenacin, one such drug, found it reduced stent symptoms but was not clearly better than an alpha-blocker alone, and combining the two did not add much benefit over either one individually.¹⁷

Why Stent Duration Matters

The longer a stent stays in, the worse it tends to feel and the higher the risk of complications. A prospective study comparing three different stent dwell times after ureteroscopy found that the group with the shortest duration had the lowest symptom scores, the least pain, the fewest painkillers consumed, the highest satisfaction, and the fastest return to normal activities. Complication rates were statistically similar across all three groups, so there was no safety penalty for removing the stent sooner. On multivariable analysis, longer stent duration was the single strongest predictor of worse symptom scores.¹⁸

Most post-procedure stents are left in for one to two weeks, though surgeons vary in their preferred timing. If you have a stent placed for ongoing malignant obstruction or a chronic stricture, it will need to be exchanged periodically, usually every three to six months for polymeric stents. Metal stents can go longer, with some studies reporting annual exchanges.²

The Danger of Forgotten Stents

One of the most avoidable complications in urology is a “forgotten” stent, one that stays in the body far beyond its intended lifespan because the patient misses follow-up or is not informed that it needs to come out. Over months and years, urine minerals precipitate onto the stent surface, forming a hard crust called encrustation. Bacteria contribute by forming biofilms that raise urine pH and accelerate crystal deposition, particularly species that produce the enzyme urease.¹⁹

A case series of patients with forgotten stents reported a mean dwell time of nearly 33 months, with one stent left in for almost seven years. Consequences included large stones forming around the stent, urinary infections, reflux of urine back toward the kidney, and ureteral polyps. Removal required multiple endoscopic procedures and careful planning.²⁰ Forcibly pulling an encrusted stent can cause ureteral tears or stent breakage, so the encrustation has to be broken up first using lasers or other lithotripsy techniques before the stent can safely come out.²¹

The broader data on stent encrustation points to dwell time as the dominant risk factor, though patient-specific conditions like chronic infection and high urinary mineral concentrations also play a role.²² The simplest prevention strategy is good follow-up: know the date your stent is supposed to come out, and do not skip that appointment.

Migration and Other Mechanical Complications

Although the curled ends of a double-J stent are designed to keep it anchored, stents can shift position. A review of over 50,000 stent procedures found proximal migration (the stent sliding up toward the kidney) in about 0.9% of cases and distal migration (sliding down toward the bladder) in about 0.7%.²³ A migrated stent usually needs a second procedure to retrieve or reposition it. Migration risk goes up with a poorly sized stent, vigorous physical activity, or a ureter that has been dilated by chronic obstruction.

Stents in Children

Ureteral stents are used in pediatric patients for many of the same reasons as in adults, including stones, post-operative drainage, and congenital urinary tract anomalies. However, children present unique challenges: their ureters are smaller, they may not tolerate stent symptoms as well, and removing a stent typically requires general anesthesia rather than an office procedure.²⁴

Pediatric stent sizing often follows an “age plus 10 centimeters” rule as a starting estimate for length. Magnetic retrieval systems, where a magnet-tipped catheter grabs a magnetic stent end in the bladder, are gaining traction because they can avoid the need for a full anesthesia episode for removal. Anti-biofilm and anti-encrustation coatings are being explored but still lack the pediatric-specific clinical validation needed for routine use.²⁵

Newer Stent Materials and Biodegradable Designs

The limitations of conventional polymer stents, particularly encrustation, biofilm, and the need for a removal procedure, have driven research into better materials. Metal stents made of nickel-titanium alloy or stainless steel offer greater radial force to resist external compression from tumors and can remain in place longer before exchange. They have shown good tolerability in patients with chronic obstruction from both benign and malignant causes.²

The most ambitious innovation is the biodegradable stent, a device designed to dissolve harmlessly in the body after a set period, eliminating the removal step entirely. Materials under investigation include polylactic acid polymers and magnesium-yttrium alloys. Early laboratory work on magnesium-based stent prototypes has shown promising degradation profiles and mechanical properties.²⁶ A practical biodegradable stent would eliminate forgotten-stent complications, reduce healthcare costs, and spare patients one procedure. Significant hurdles remain, though, including controlling the degradation rate precisely enough to match different clinical scenarios and ensuring that the dissolving material does not itself cause irritation or obstruction. No biodegradable ureteral stent has entered routine clinical practice yet, but the field is active and the motivation is clear: the biggest problem with ureteral stents is that they have to come out, and a stent that disappears on its own would change the calculus for patients and clinicians alike.