Kidney Stone Risk Panel

A kidney stone risk panel is used to help evaluate the likelihood that an individual who has had two or more kidney stones will develop additional ones, indicating a recurrent problem.

Testing is sometimes used to evaluate risk after an initial occurrence of a stone if a person is considered to be at an especially elevated risk for forming more stones or for a person who is likely to develop kidney dysfunction if another kidney stone is formed.

This testing may be used to help guide and monitor the treatment of someone who has had a kidney stone.

Several other laboratory tests may also be used to help evaluate a person who has had a kidney stone, including:

• Individual 24-hour urine tests that may not be part of the kidney stone risk panel, such as cystine, sodium, potassium, chloride, or magnesium
• A urinalysis to evaluate urine constituents (substances, protein, red and white blood cells, pH, and presence of crystals or bacteria)
• Blood tests such as a blood urea nitrogen (BUN) and creatinine to evaluate kidney function, electrolytes (sodium, potassium, chloride, bicarbonate) and calcium to evaluate health status and compare to urine results
• A urine culture If a person shows signs of a urinary tract infection
• Kidney stone analysis is usually performed to evaluate the specific substances present in the stone, if the kidney stone is able to be collected.

A kidney stone risk panel is usually performed several weeks after a kidney stone has been resolved and is frequently run in duplicate on two different 24-hour urine sample collections to determine whether elevated levels of a substance are temporary or persistent.

In most cases, testing will be ordered when a person has had a second kidney stone develop, but it may be ordered after a first stone when a person is considered to be at an increased risk of stone formation or kidney dysfunction. This may include people who:

• Formed stones as a child
• Have a family history of kidney stones
• Had multiple kidney stones at the same time as their "initial" stone
• Have a single functional kidney, including those who have had a kidney transplant

Sometimes testing may be performed when a person has made changes to their lifestyle (such as recommended dietary changes or drinking more water) or medication changes in order to monitor the effectiveness of these changes.

The results of the kidney stone risk panel are evaluated in conjunction with other tests performed in order to help determine a person's likely risk of developing another stone.

In general, if a substance, such as calcium or uric acid, is present in excess in both the blood and urine, then it represents an increased risk for kidney stone formation and a condition that should be further investigated to determine the cause.

Test results cannot predict, however, who will actually develop another kidney stone or when.Some people with mild elevations, or even results within normal ranges, may form stones, while other people with significantly increased results will not.

In a person who has made lifestyle or medication changes, decreasing levels represent a decreased risk of stone formation.

If a person is dehydrated, then the amount of urine produced in 24-hours (urine volume) will be low and the urine will be more concentrated. This can cause an excess of a substance per volume (dissolved in less liquid) and increase the likelihood of stone formation.

Kidney stone formation is also affected by urine pH (acidic/alkaline). Uric acid and cystine crystals can only form in acidic urine, while calcium phosphate and struvite stones form in alkaline urine. Struvite stones consist of magnesium ammonium phosphate and are associated with bacterial infections.

The table below summarizes what some test results may indicate:

Other less common tests are summarized below:

Kidney stones may be as small as a grain of sand, as large as a golf ball, or even larger, with some filling up the entire collecting system of the kidney. These are sometimes called "staghorn" calculi because the shape of the collecting system resembles the antlers of a deer. They can cause problems either because they grow large enough to obstruct urine flow or because they become dislodged or break off and begin to travel from a kidney through the ureter, where they can cause temporary obstruction and stretch, irritate, and/or damage the walls of the ureter. This movement can cause abrupt, extremely severe pain that may be intermittent or continuous.

Many stones will eventually pass out of the body in the urine, but some are too large or have too irregular a shape for the body to expel. With very large stones, which typically cannot pass from the kidney into the ureters, and for smaller stones that get into but do not pass through the ureters, some form of treatment is needed.

Not everyone who drinks too little liquid or who has an excess amount of substances in their urine will form kidney stones. Some stones will form in people for other reasons. Those who have had one kidney stone are at an increased risk for stone recurrence.

Abnormalities in the structure of the kidneys and/or urinary tract may cause the flow of urine to be impeded and crystals to be deposited, leading to formation of stones.

Struvite (magnesium ammonium phosphate) stones are associated with urinary tract infections.