You should go to the hospital for a kidney stone when you have a fever with chills, pain so severe that no position brings relief, vomiting that prevents you from keeping down fluids or medication, or you stop being able to urinate. Any of these signals a situation your body can’t resolve on its own and that can become dangerous within hours if left untreated.
Most kidney stones do pass without surgery, but the line between “painful but manageable” and “medical emergency” isn’t always obvious. Here’s how to tell the difference.
Signs That Require an ER Visit
Five specific symptoms mean you should get to an emergency room rather than waiting it out:
- Fever or chills alongside flank pain. This combination suggests the stone is trapping bacteria behind it, creating an infected, obstructed kidney. That infection can spread to your bloodstream (urosepsis) quickly, and the only fix is relieving the blockage and starting antibiotics. A temperature above 101°F (38.3°C) with stone symptoms is not something to watch overnight.
- Pain you cannot control at home. Kidney stone pain comes from pressure building behind the blockage. If over-the-counter pain relievers aren’t touching it and you can’t sit still, lie down, or find any comfortable position, the obstruction likely needs to be relieved directly. That requires hospital-level intervention.
- Nausea and vomiting that won’t stop. Persistent vomiting is a problem on two fronts: you become dehydrated, which makes passing the stone harder, and you can’t absorb oral pain medication. You’ll need IV fluids and IV pain relief.
- Inability to urinate. If urine flow drops to a trickle or stops entirely, the stone may be causing a complete blockage. This is especially urgent because a fully obstructed kidney begins to sustain damage within hours.
- Blood in your urine. Some pink or reddish urine is common with stones and isn’t always an emergency on its own. But heavy, persistent blood in your urine, particularly combined with other symptoms on this list, warrants immediate evaluation.
Why Infection Is the Most Dangerous Scenario
A kidney stone that blocks urine flow while bacteria are present creates a closed-off pocket of infection. Your body can’t flush the bacteria out, and antibiotics alone can’t reach it effectively. The infection builds pressure, and bacteria can spill into your bloodstream. Early signs include fever, chills, a racing heart rate, rapid breathing, and feeling much sicker than the pain alone would explain.
When this happens, the blockage must be relieved immediately, usually by placing a small tube (stent) past the stone or inserting a drainage catheter through the back directly into the kidney. This is done before any stone removal procedure. People who are immunocompromised, have diabetes, or take medications that suppress the immune system are at higher risk for this progression.
How Stone Size Predicts Whether You’ll Need Help
The size of your stone is the single best predictor of whether it will pass on its own. A large study tracking nearly 400 stones found clear thresholds:
- 3 mm or smaller: 98% pass without intervention
- 4 mm: 81% pass on their own
- 5 mm: 65% pass on their own
- 6 mm: only 33% pass on their own
- 6.5 mm or larger: only 9% pass on their own
If you’ve had imaging that shows your stone is under 5 mm, your doctor may recommend managing symptoms at home with pain medication and plenty of fluids while waiting for it to pass. That process can take days to several weeks. Stones 6 mm and above usually require a procedure because the odds of spontaneous passage drop dramatically. Location matters too: a stone that has already traveled into the lower portion of the ureter (the tube connecting kidney to bladder) is closer to the exit and more likely to pass than one still near the kidney.
What Happens to Your Kidney During a Blockage
When a stone fully blocks the ureter, urine backs up and the kidney swells, a condition called hydronephrosis. The pressure reduces blood flow to the kidney and triggers inflammation. Research on obstructed kidneys shows that tissue-level damage begins within about two hours of a complete blockage, though meaningful functional loss takes longer to develop.
The reassuring news: obstruction lasting less than one week typically results in complete recovery of kidney function once the blockage is cleared. Prolonged obstruction over six to eight weeks, however, can cause irreversible scarring. This is why stones that cause persistent, worsening symptoms shouldn’t be ignored for weeks on end, even if the pain comes and goes. The kidney can be quietly losing function while you wait.
If You Have One Functioning Kidney
People with a single kidney, whether from birth, prior surgery, or a transplant, should treat any stone symptoms as more urgent. A blockage in your only functioning kidney puts all of your kidney function at risk at once, not just half.
Kidney transplant recipients face an additional challenge: the transplanted kidney has severed nerve connections, which means pain signals are often muted or absent. Stones in transplant kidneys are more frequently discovered late, after swelling or reduced function has already developed. Transplant recipients are also more susceptible to urinary tract infections, so the combination of a stone and infection can escalate faster. If you have a transplant kidney and notice any change in urine output, mild discomfort near the graft, or signs of infection, get evaluated promptly rather than waiting for severe pain that may never come.
What to Expect at the Emergency Room
The ER’s first priorities are controlling your pain, checking for infection, and determining the size and location of the stone. You’ll typically get IV pain relief and anti-nausea medication quickly. Blood work will check your kidney function and white blood cell count, and a urine sample will screen for infection and blood.
The standard imaging test is a low-dose CT scan of your abdomen and pelvis, done without contrast dye. This scan is 99% sensitive for detecting stones and provides precise information about the stone’s size, location, and whether it’s causing significant swelling in the kidney. It uses considerably less radiation than a standard CT. In some cases, especially for pregnant patients or children, ultrasound is used first, with CT reserved for unclear results.
Based on the results, you’ll either be sent home with a pain management plan and a follow-up appointment (for small stones likely to pass), or admitted for a procedure to remove or bypass the stone. Most people who come to the ER for kidney stones are treated and discharged the same day, with instructions on what to watch for at home.
When It’s Okay to Manage Symptoms at Home
Not every kidney stone requires a hospital visit. If your pain responds to ibuprofen or a similar anti-inflammatory, you’re able to keep fluids down, you have no fever, and you can still urinate, it’s generally safe to manage at home while the stone passes. Drink enough water to keep your urine light yellow. Straining your urine through a fine mesh can help you catch the stone so it can be analyzed later.
The situation to watch for is a change in pattern. Pain that was manageable but suddenly becomes unbearable, a new fever developing days into the episode, or urine output dropping off are all reasons to reassess. Kidney stones are unpredictable: a stone that was moving along fine can get wedged in a narrow spot and shift from a home-management situation to an emergency within hours.