About 11 percent of men and 6 percent of women in the United States will pass a kidney stone at some point in their lives, according to the National Institute of Diabetes and Digestive and Kidney Diseases. That works out to roughly 1 in 10 Americans, and the numbers have been rising for decades.
The problem is that a stone rarely announces itself clearly. Early signs are easy to write off as a urinary tract infection, a pulled muscle or an unsettled stomach, so people wait, drink some water and hope it passes. Sometimes it does. Sometimes it lodges somewhere it should not and turns into an emergency.
What a kidney stone actually is
A kidney stone is a hard deposit of minerals and salts that forms inside the kidney when substances like calcium, oxalate and uric acid become too concentrated in the urine. Small stones can pass unnoticed. Larger ones scrape the urinary tract or get stuck, which is when the trouble starts.
7 warning signs worth knowing
The National Kidney Foundation and the NIDDK describe the same recognizable pattern. Any one of these signs alone may not mean much. Two or three together are a reason to call your doctor.
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1. Sharp pain in the side, back or lower abdomen. The classic sign. The pain often starts below the ribs on one side and radiates toward the groin as the stone moves down the ureter. It tends to come in waves rather than as a constant ache, which is what separates it from a pulled muscle.
2. Blood in the urine. Pink, red or brown urine is a hallmark sign, according to the NIDDK. The stone scrapes the lining of the urinary tract as it moves, and the blood may be visible or only show up on a lab test.
3. Nausea and vomiting. The kidneys and the digestive tract share nerve pathways, so intense kidney pain often triggers an upset stomach. Many people mistake this for a stomach bug until the flank pain sets in.
4. A constant urge to urinate. Once a stone reaches the lower urinary tract, it can create a feeling of needing to go, again and again, often with little coming out. This is one of the signs most frequently mistaken for a bladder infection.
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5. Pain or burning when you urinate. Another symptom that mimics a UTI. The burning happens as the stone irritates the urethra or bladder outlet.
6. Cloudy urine. Cloudy urine can point to infection or to crystals and debris shed by a stone. When it appears alongside flank pain, the combination is more suggestive of a stone than a plain UTI.
7. Foul-smelling urine. A strong or unusual odor, especially with any of the signs above, can suggest infection developing behind a blockage. That is a situation that needs medical attention quickly.
When it becomes an emergency
Most stones pass on their own within a few weeks. If yours does not, Cleveland Clinic advises seeing a doctor for imaging and a plan. Some situations, though, cannot wait. Pain that becomes unbearable, fever and chills alongside flank pain (which can signal an infected, obstructed kidney that turns septic within hours), an inability to urinate, or vomiting so persistent that you cannot keep fluids down are all reasons to head to the emergency department.
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How to lower the odds of a next one
Once you have had a kidney stone, your risk of a second one climbs sharply, which is why prevention matters. A 2023 review in Advances in Nutrition pulled the best-supported dietary steps together in one place.
Fluid is the single most consistent factor. Guidelines cited in the review recommend a urine output above 2 to 2.5 liters a day, achieved with a fluid intake of roughly 2.5 to 3 liters. Hot weather, exercise and sweaty workouts push that number up, not down.
Salt is the next lever. High sodium intake drags calcium into the urine, where it becomes a building block for stones. The bulk of American sodium comes from processed and restaurant food, not the salt shaker.
Animal protein deserves a closer look too. Diets heavy in meat lower urine pH and citrate and raise uric acid, all of which favor stone formation. The review suggests moderating animal protein rather than loading up on it at every meal.
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The most counterintuitive rule is about calcium. Cutting calcium to prevent stones actually backfires. The National Kidney Foundation recommends normal dietary calcium intake, ideally from food taken alongside meals, so the calcium can bind oxalate in the gut before it ever reaches the kidneys.
None of this replaces a workup by a urologist or nephrologist, who can analyze a passed stone and tailor advice to its chemistry. Anyone with recurring stones, or with symptoms that fit the list above, should talk to their doctor rather than manage it alone.
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This article is made and published by Jesper Bengtson, who may have used AI in the preparation.