Kidney Stones Are Excruciating, But the Source of Pain Is Surprising

Every year, half a million people visit emergency rooms across the country with kidney stones, and around one in 10 Americans will have a kidney stone at some point in their life. You have two kidneys, and their main job is to filter waste products out of the blood. Normally, those waste products are flushed out of the kidney as urine. Your kidneys filter 50 gallons of blood every 24 hours and eliminate about 64 ounces of waste. In some cases, however, there are excess waste products in the blood that aren't flushed out of the kidneys. Those leftover waste products can form tiny crystals that bunch together over time to form increasingly large "stones." The real trouble starts when one of those stones leaves the kidney and enters the ureter, a narrow tube that transports urine from the kidney to the bladder. That's when it can feel like you've been stabbed in the back. The common belief is that the stone itself causes the pain, but stone have nothing to do with the pain. With a kidney stone stuck in the narrow passageway of the ureter, the urine has nowhere to go. As it increases, it puts pressure on the ureter and kidney, causing the tissues to stretch like a balloon. That stretching is what causes the pain that people feel, and it’s excruciating. Another common misconception is that the most painful part of having a kidney stone is passing it. In both men and women, the urethra is much wider — almost twice the size — than the ureter. For that reason, most people don’t even know when the stone has passed.