Kidney Stone Analysis

Test Overview

Kidney stone analysis is a test done on a kidney stone to see what chemicals are in it. The test is done on a kidney stone that has been passed in the urine or removed from the urinary tract during surgery. Chemical analysis of a kidney stone shows the type of stone which can guide treatment and give information that may prevent more stones from forming. People who have had a kidney stone have a chance of having another one, so prevention measures are important.

A kidney stone (renal calculus) forms in the kidney from substances that would normally pass out of the body in the urine. When there are large amounts of these substances, they separate from the urine and form kidney stones.

A kidney stone can be as small as a grain of sand or as large as a golf ball. Sometimes a stone may leave the kidney and move down a ureter into the bladder. From the bladder, the stone passes through the urethra and out of the body in urine. Passing a kidney stone through a ureter or the urethra may be painless or it may cause severe pain. A kidney stone may cause other symptoms, such as blood in the urine (hematuria), pain when urinating, or a severe need to urinate.

Why It Is Done

A kidney stone analysis is done to:

• Find the chemical makeup of a kidney stone.
• Guide treatment for a kidney stone.
• Give information on how to prevent more kidney stones from forming.

How To Prepare

If you think you might have a kidney stone, talk to your doctor. You may be told to collect the stone by straining your urine through a fine-mesh strainer or through fine gauze. Your doctor may give you a kidney stone strainer, or you may buy one from a drugstore.

How It Is Done

Straining the first urine specimen of the morning is important. That's because a stone may pass into your bladder during the night.

Look carefully at the strainer for a kidney stone. It may look like a grain of sand or a small piece of gravel. Any stone you find should be kept dry—do not put it in fluid or urine. Put it in a cup with a lid or in a plastic bag. Take it to the doctor's office or lab for analysis. Do not put tape on the kidney stone. Tape can change the test results.

The kidney stone you take to the lab will be cleaned of any blood or tissue and then looked at to find what chemicals it is made of.

How It Feels

The most common way a kidney stone is collected for this test is by passing it in urine. Passing a stone may be painless or it may be very painful. The pain can begin suddenly and may come and go. A sand-sized stone may pass with little pain. A larger stone may cause a lot of pain in the lower back, groin, or genitals as it moves down the ureters or the urethra.

A small stone may pass without medical treatment. A large stone may need surgery or another type of procedure to get it out.

Risks

There is no chance for problems with kidney stone analysis. But a kidney stone can:

• Have bacteria that can cause a urinary tract infection (UTI).
• Damage the kidney, especially if the stone is a staghorn (struvite) stone.
• Block the urinary tract. This can happen while the stone is passing through the tract.

Results

Knowing the type of kidney stone helps guide the best treatment choice. Your doctor will talk with you about treatment and prevention measures.

• About 80% of kidney stones are made of calcium oxalate, calcium phosphate, or a combination of both.^{footnote 1}
• About 10% to 15% of kidney stones are made of magnesium ammonium phosphate (struvite).^{footnote 1}
• About 5% to 10% of kidney stones are made of uric acid.^{footnote 1}
• Less than 1% of kidney stones are made of a chemical called cystine.^{footnote 1}