What Size Is a Kidney Stone?

Some kidney stones will remain in the kidney and never cause any problems. Others will move out of the kidney and into the ureter. That's when potential problems and pain arise. The severity of the symptoms and whether medical intervention is necessary depends on the size and shape of the kidney stone.

Definition

• The kidneys are responsible for two very important functions: They remove wastes from the blood and they control the volume of blood by removing or restoring water. The waste products include minerals that normally remained dissolved in the urine, but under certain conditions, they form into tiny crystals. Over time the crystals clump together and develop into stones.

Causes

• Stones can form if there isn't enough water in the urine to completely dissolve waste products or if there is a high level of the substances that typically form into stones---calcium and oxalate. Urine normally contains chemicals that help stop crystals from forming and if they are low, there is an increased chance of a stone forming.

Description

• Kidney stones can be smooth, jagged or staghorn shaped. Many sources state that the size of a kidney stone ranges from being as tiny as a grain of sand to becoming as large as a golf ball. Researchers at the University of Missouri published a study about treatment for "large" kidney stones in the Journal of Endourology in September 2009. They considered any kidney stone over 2.5 cm (almost one inch) to be large and the average size of the stones in their study was 3 cm. A news report in Great Britain in January 2009 showed the picture of a kidney stone that weighed 2.5 pounds and was the size of a coconut. This is very rare but it highlights the fact that every body is different. The size and shape play an important role if the stones move out of the kidney.

Significance

• Kidney stones that remain in the kidney usually cause no symptoms. Once they leave the kidney, severe pain is experienced as they move into the urinary tract. This is where size and shape are important. A smooth, small stone passes through the ureter more easily than a larger, jagged one. Any stone will cause pain but if it is too large to easily pass through the narrow tubes of the ureter, pain continues as the smooth muscles try to push the stone through the ureter. Stones that are too large or jagged are more likely to get stuck, then the flow of urine can be blocked, pain increases, and an infection can start.

Treatment

• Physicians at the Delaware Urological Associates state that kidney stones that are larger than 1 cm (0.39 inches) will "rarely pass through the urinary system without complications." They also note that the chance of a stone passing naturally through the ureter without intervention depends on the size of the stone. "For stones less than 3 mm in width, the chance of spontaneous stone passage is very high. Stones more than 8 mm in width are only about 20% likely to pass spontaneously over one year."

  If your physician recommends allowing the stone to pass through the urine naturally, you may be prescribed medication for pain and you'll need to drink a lot of water. If intervention is needed, the first choice is extracorporeal shock wave lithotripsy (ESWL). This sends shock waves through the body that don't harm other tissues, but that will break stones into smaller pieces that can be passed through the urine. If the stone is too large, other minimally invasive techniques or surgery may be necessary.