Obstructed Kidney Stone: Symptoms and Treatments

A kidney stone that blocks the flow of urine out of the kidney triggers an escalating cascade of pain, pressure, and potential organ damage. The hallmark symptom is sudden, severe flank pain that radiates toward the groin, often accompanied by nausea, vomiting, and blood in the urine. But an obstructing stone is more than a pain problem: left untreated, the backup of urine can stretch the kidney, impair its function, and set the stage for serious infection. How the stone is managed depends on its size, its exact location, and whether complications like infection or kidney injury are already underway.

Why an Obstructing Stone Hurts So Much

Kidney stones form inside the kidney and often cause no symptoms until they move into the ureter, the narrow tube connecting the kidney to the bladder. The ureter is only a few millimeters wide, so even a small stone can wedge in place and block the passage of urine. The backed-up urine distends the kidney and the renal pelvis, a condition called hydronephrosis. That distension activates stretch receptors and pain fibers in the kidney capsule, producing what is commonly called renal colic: waves of intense pain that wax and wane as the ureter spasms around the stone.

There are three spots in the ureter where stones are most likely to get stuck: the junction where the kidney meets the ureter at the top, the point where the ureter crosses over the pelvic blood vessels in the mid-abdomen, and the very bottom where the ureter enters the bladder wall.¹ Each of these narrowings is a natural chokepoint where the tube’s diameter is smallest. Where the stone lodges influences both the pattern of pain and the likelihood that it passes on its own.

Symptoms Beyond the Pain

Renal colic is the most dramatic symptom, but it is not the only one. The classic presentation includes sharp pain in the flank or lower back that may shoot down into the lower abdomen, groin, or inner thigh on the affected side. The pain often comes in waves lasting 20 to 60 minutes, separated by intervals of dull aching. Many people feel nauseated or vomit during the worst spasms. Visible blood in the urine, or blood detected on a urine test, is common because the stone scrapes the lining of the ureter as it moves.

When the stone sits near the bladder, symptoms can mimic a urinary tract infection: frequent urination, a burning sensation, and an urgent feeling of needing to go despite producing only small amounts of urine. Some people develop a low-grade fever even without infection, though any fever above about 38°C (100.4°F) with an obstructing stone should be treated as a red flag.

When an Obstructing Stone Becomes an Emergency

Most obstructing stones are painful but not immediately dangerous. A few scenarios, however, demand urgent medical attention. The most serious is an infected obstructed system, sometimes called pyonephrosis. When bacteria are trapped behind a blockage, infection can escalate rapidly into sepsis. Urinary tract infection and sepsis from obstructing ureteral stones are considered true urological emergencies, and physicians are advised to maintain a high index of suspicion for the diagnosis.² Signs include high fever, chills, rapid heart rate, and feeling very unwell on top of the typical stone pain.

Another emergency is bilateral obstruction, where stones block both ureters at the same time. This is rare, but when it happens, urine has no way out and the kidneys begin to fail. Anuria, meaning no urine production at all, is the hallmark. One case report documented bilateral obstructing stones causing acute kidney injury along with a dangerous buildup of lactic acid in a patient taking metformin, because the kidneys could no longer clear the drug.³ People with a single functioning kidney face a similar risk from a single obstructing stone.

If you have stone pain along with fever, inability to urinate, or signs of severe illness, that is a situation requiring emergency care, not a wait-and-see approach.

How Doctors Confirm the Obstruction

A non-contrast CT scan is the standard for diagnosing ureteral stones and evaluating obstruction. It is fast, highly accurate, and shows stone size, location, and whether the kidney is swollen from backed-up urine. Ultrasound is sometimes used as a first step, especially in pregnant patients or when avoiding radiation is a priority, but it is less reliable. One study found ultrasound had a sensitivity of about 77% for detecting kidney stones, meaning it misses roughly one in four.⁴ That said, ultrasound can reliably show hydronephrosis, which is indirect evidence that something is causing a blockage even if the stone itself is not visible.

Blood tests typically accompany imaging. A basic metabolic panel checks kidney function, and a complete blood count and inflammatory markers help rule out infection. A urinalysis looks for blood, white blood cells, and bacteria. Together, these tests tell the treatment team whether the kidneys are coping, whether infection is present, and how urgently intervention is needed.

Managing the Pain

Renal colic ranks among the most severe forms of acute pain. The first priority in any emergency department visit for an obstructing stone is getting pain under control. Anti-inflammatory painkillers are the first-line option. A Cochrane review comparing anti-inflammatory drugs to opioids for acute renal colic found that patients given anti-inflammatories were less likely to need rescue medication and experienced significantly less vomiting.⁵ A later meta-analysis confirmed a modest pain-reduction advantage for anti-inflammatories over opioids and reinforced the lower rate of vomiting and fewer rescue treatments needed.⁶

Anti-inflammatories work particularly well for stone pain because part of the pain comes from prostaglandin-driven inflammation in the ureter wall, not just from mechanical stretching. Opioids are still used when anti-inflammatories are not enough or are contraindicated, but they tend to cause more nausea and do not address the underlying inflammation. Acetaminophen (paracetamol) is sometimes added as a supplement but is generally less effective as a standalone agent for this kind of pain.

Will the Stone Pass on Its Own?

Many obstructing stones do eventually pass without surgery, especially smaller ones. The critical variable is size. One large study found spontaneous passage rates of about 98% for stones up to 3 mm, dropping to roughly 65% for 5 mm stones, about a third for 6 mm stones, and under 10% for stones 6.5 mm or larger.⁷ Location matters too. Stones closer to the bladder pass more readily than those stuck near the kidney. An earlier study using CT imaging reported passage rates of about 48% for stones in the upper ureter, 60% in the mid ureter, and 75–79% for stones near or at the bladder.⁸

Conservative management, sometimes called watchful waiting or a “trial of passage,” is typically offered when the stone is under about 8 mm in width, there is no infection, kidney function is adequate, and pain is manageable.⁹ You are usually told to drink plenty of fluids, take pain medication as needed, and strain your urine to catch the stone when it passes. A follow-up imaging study is typically scheduled within a few weeks to make sure the stone is progressing and the kidney is not getting worse.

Medical Expulsive Therapy

Medications can improve the odds and speed of passage for stones in the lower ureter. The most commonly prescribed drug for this purpose is tamsulosin, an alpha-blocker originally developed for prostate symptoms. It relaxes smooth muscle in the ureter wall, widening the channel and reducing spasms. A systematic review and meta-analysis of randomized trials found that tamsulosin was associated with a roughly 44% higher stone expulsion rate compared to placebo or no treatment, along with shorter time to passage and fewer episodes of colic.¹⁰ A single-center trial reported stone expulsion in about 90% of patients receiving tamsulosin versus roughly 71% in the control group, with patients on the drug needing fewer analgesics and passing their stones several days sooner on average.¹¹

Another option explored in research is tadalafil, a drug better known for erectile dysfunction that also relaxes smooth muscle. A prospective trial comparing the two found an expulsion rate of about 84% with tadalafil versus 68% with tamsulosin, along with fewer colic episodes in the tadalafil group.¹² Medical expulsive therapy is generally offered for distal ureteral stones under about 10 mm when there is no urgent reason to intervene surgically. It is not a substitute for surgery when infection, severe pain, or worsening kidney function is present.

Surgical and Procedural Options

When a stone is too large to pass, when conservative management fails, or when complications demand it, procedural intervention is the next step. The two most common approaches for ureteral stones are ureteroscopy and shockwave lithotripsy.

Ureteroscopy involves passing a thin, flexible scope through the urethra, bladder, and into the ureter. Once the stone is visualized, it is broken into fragments using a laser (most commonly a holmium laser) and the pieces are extracted with a tiny basket. This approach has high stone-free rates: one study of impacted upper-ureter stones reported an 80% clearance rate at one month with ureteroscopy versus about 68% with shockwave lithotripsy.¹³ A large randomized trial in the UK (the TISU trial) found that patients who underwent shockwave lithotripsy had about double the rate of needing further treatment compared to ureteroscopy, though shockwave lithotripsy was less expensive and still considered cost-effective for certain patients.¹⁴

Shockwave lithotripsy (SWL), by contrast, is noninvasive. Focused shockwaves are aimed at the stone from outside the body, breaking it into smaller fragments that the patient then passes naturally. The trade-off is a lower one-session clearance rate and the possibility of needing repeat sessions. It works best on smaller stones that are not too dense, and it is less effective for stones in certain locations or those that are very hard (like calcium oxalate monohydrate).

For very large kidney stones or complex situations, percutaneous nephrolithotomy (PCNL) is an option. A small incision is made in the back, and a scope is passed directly into the kidney to break up and remove the stone. This is reserved for stones too big for ureteroscopy or shockwave treatment.

Emergency Drainage Procedures

When an obstructing stone is accompanied by infection or the kidney is in acute danger, the immediate priority is restoring urine flow rather than removing the stone. Two methods are used: placing a ureteral stent through the bladder and up past the blockage, or inserting a percutaneous nephrostomy tube directly through the back into the kidney.

A randomized trial comparing the two in patients with stone-related obstruction found no meaningful difference in recovery time, with both groups recovering in roughly one and a half to two days on average.¹⁵ When active urosepsis (systemic infection from a urinary source) is present, there is some evidence that nephrostomy tubes may resolve fever and inflammation faster.¹⁶ In practice, the choice often comes down to which procedure is technically feasible: if a stent cannot be passed beyond the stone, a nephrostomy is the fallback. These are temporary measures. Definitive stone treatment happens once the infection has cleared and the patient has stabilized.

Life with a Ureteral Stent

After ureteroscopy or emergency drainage, many patients go home with a ureteral stent in place. This thin, flexible tube holds the ureter open while it heals. Stent-related symptoms are extremely common, affecting over 80% of patients.¹⁷ Symptoms include frequent urination, urgency, a burning sensation when urinating, flank pain with a full bladder, and sometimes blood in the urine. Many people describe the stent as more bothersome than the stone itself.

Research suggests the diameter of the stent influences how much discomfort patients experience, with wider stents associated with worse urinary symptoms.¹⁸ Stents are typically left in place for a few days to several weeks, depending on the clinical situation. Alpha-blockers (the same tamsulosin used for medical expulsive therapy) are sometimes prescribed to reduce stent-related discomfort, and staying well-hydrated helps dilute the urine and reduce irritation. The stent is removed in a brief office procedure using a cystoscope.

Kidney Stones During Pregnancy

Pregnancy complicates both diagnosis and treatment. Ultrasound is recommended as the first-line imaging modality because it avoids radiation.¹⁹ However, the normal physiological dilation of the ureters during pregnancy can mimic obstruction on ultrasound, making interpretation tricky. MRI without contrast is sometimes used as a second-line study when ultrasound is inconclusive.

First-line management in pregnancy is conservative: pain control (acetaminophen is preferred over anti-inflammatories in later pregnancy), hydration, and a trial of passage. The good news is that conservative management is associated with a high rate of stone passage in pregnant patients.²⁰ When an infected obstructed system develops, immediate drainage with either a ureteral stent or nephrostomy tube is required, just as in non-pregnant patients. If conservative management fails and no infection is present, ureteroscopy can be offered with appropriate precautions. Shockwave lithotripsy and percutaneous nephrolithotomy are both contraindicated in pregnancy.

Preventing the Next Obstruction

About half of people who pass a kidney stone will form another one within five to ten years. Once you have had an obstructing stone, understanding what kind of stone it was matters for prevention. If you catch the stone by straining your urine, your doctor can send it for analysis. The most common type is calcium oxalate, but uric acid stones, calcium phosphate stones, struvite stones, and cystine stones each call for different dietary and medical strategies.

A thorough metabolic evaluation typically involves blood work and a 24-hour urine collection to measure levels of calcium, oxalate, citrate, uric acid, sodium, and other substances that influence stone formation.²¹ This is most commonly recommended for recurrent stone formers or people with complex medical histories, though some urologists will offer it after a first stone if the stone was large or if risk factors are present. The results guide specific recommendations: increased fluid intake (enough to produce over two liters of urine daily) is universal advice, but dietary changes like reducing sodium and animal protein, increasing citrus intake, and adjusting calcium consumption depend on what the urine analysis reveals.

For people with recurrent calcium stones and high urinary calcium, a thiazide diuretic may be prescribed to reduce calcium excretion. For recurrent uric acid stones, potassium citrate alkalinizes the urine and prevents uric acid crystallization. Struvite stones, which form in the setting of chronic infection with certain bacteria, require both stone removal and treatment of the underlying infection to prevent regrowth.

Burst Wave Lithotripsy and the Future of Stone Treatment

The most watched development in kidney stone treatment is burst wave lithotripsy (BWL), a noninvasive technique that uses focused ultrasound at lower amplitudes and higher frequencies than conventional shockwave lithotripsy. Early data suggest it can fragment stones in awake patients without significant pain or kidney injury.²² A related technology called ultrasonic propulsion uses focused ultrasound pulses to push stone fragments down the ureter after fragmentation.

A recent feasibility study demonstrated that small, asymptomatic renal stones could be effectively and safely fragmented and expelled in awake participants in a clinic setting using a combination of BWL and ultrasonic propulsion.²³ The potential appeal is enormous: imagine treating a stone in an office visit, without anesthesia, sedation, or an operating room. The technology is still in clinical trials and is not yet widely available, but it represents a meaningful shift toward less invasive management. If larger studies confirm the early results, BWL could eventually fill the gap between watchful waiting and surgical procedures, offering an intermediate option for stones that are unlikely to pass on their own but do not yet warrant a trip to the operating room.²⁴