Kidney stones are hard deposits that form in the kidneys, made up of minerals that are normally present in urine. They can vary in size, from as small as a grain of sand to as large as a nickel, occasionally even larger. Sometimes they lodge in the kidney, and sometimes they break free and make their way out through the urinary tract, which can be extremely painful.
Kidney stones can be smooth or jagged and are yellow to brown in color. They are mostly comprised of the minerals calcium, oxalate, and phosphorus. Examining the stones to see what they are made of can show what caused the stone to be formed in the first place. For example, a stone made of mostly calcium, which is the most common type, can happen any time the urine becomes too concentrated due to dehydration or a blockage in the kidney. A uric acid stone forms when acid levels in the urine get too high, usually due to excessive consumption of animal protein such as meat and fish. A struvite stone is a sign of certain infections, and a cystine stone can be due to a genetic disorder that raises the risk of kidney stones.
The most common symptom of kidney stones is pain, either in the back or lower abdomen, or severe pain when urinating. There may also be blood in the urine. Treatment for kidney stones depends on how large the stone is. Very small stones can pass out of the body on their own, and they do not require treatment other than drinking adequate water and taking pain killers. Larger stones need to be broken apart and removed. The main treatment options are:
- Shock wave lithotripsy, which uses sound wave vibrations to break apart the stone
- Percutaneous nephrolithotomy, or the use of a very tiny tool (like a wire inserted through the back) to break apart and remove the stone
- Ureteroscopy, a thin tube inserted through the urethra and bladder to the stone, where tiny tools can grasp the stone and remove it
People who have had one kidney stone are at risk of developing another. To reduce this risk, patients are given instructions specific to the type of stone they developed. Generally the instructions will include drinking more water to dilute the urine, but it may also involve lowering sodium intake or eating less meat.