A kidney stone (nephrolithiasis) starts as tiny crystals. They form inside the kidney where urine is made. Most kidney stones enlarge to about 1/8 to 1/4 inch in size before leaving the kidney and moving toward the bladder. There are four types of kidney stones. Most (80%) are calcium stones—mostly calcium oxalate but also some with calcium phosphate. The other three types include uric acid stones, struvite stones (from a preceding infection), and rarely, cystine stones.
When the stone breaks free and starts to move down the ureter (the narrow tube joining the kidney to the bladder), it often causes sharp, severe back and side pain. Nausea and vomiting also often occur. When the stone reaches the bladder, the pain stops. After it's in your bladder, the kidney stone may pass through the urethra (urinary opening) while you are urinating (which may cause pain to start again). Or it may break into such small fragments that you don't notice it passing.
Your kidney stone is still inside your kidney. There's no way to predict how long it will be before it breaks free and causes any symptoms. Most stones will pass on their own within a few hours to a few days (sometimes longer). You may notice a red, pink, or brown color to your urine. This is normal while passing a kidney stone. A large stone may not pass on its own and may require special procedures to remove it. These procedures include:
- Lithotripsy. This uses ultrasound waves to break up the stone.
- Ureteroscopy. A thin, basket-shaped instrument is pushed through the urethra and bladder to pull out the stone.
- Surgery. This is done directly through the skin.