To help evaluate a person's risk of developing a kidney stone; to help determine the underlying reason for a kidney stone; to help guide and monitor treatment
Kidney Stone Risk Panel
When you have had two or more kidney stones and a health practitioner wants to evaluate your risk of developing additional kidney stones; when you have developed one kidney stone and are a child or have risk factors such as a family history of kidney stones, a single functional kidney, or a transplanted kidney; when the stone is found to be of unusual composition.
The kidney stone risk panel is a group of tests that measure the amounts of substances in urine that are commonly associated with kidney stone formation. In an individual who has already had kidney stones, an increased concentration of one or more of these substances can indicate both an elevated risk for developing additional stones and the likely type of stones that would form.
Kidney stone is a term for solid aggregates of minerals and salts that form in the kidneys. Typical kidney stones are composed of calcium oxalate, calcium phosphate, cystine, or uric acid.
These stones can form for several reasons, but the most common is because there is a high concentration of a particular substance or substances in the urine that precipitate and form crystals. The composition of the stone depends upon the substances present in excess. It may be all one compound or have different compounds in different layers. The majority of stones, about 75%, will contain calcium.
Kidney stone risk panels are intended to evaluate the risk of forming stones by testing for high concentrations of common stone-forming substances or low concentrations of stone-inhibiting substances. The specific tests included in a panel may vary somewhat from laboratory to laboratory but will typically include the following:
- Urine calcium
- Urine oxalate (oxalic acid)
- Urine uric acid (urate)
- Urine creatinine (does not cause stones but is used to tell if all urine was collected and help identify how concentrated the urine is)
- Urine citrate (citric acid; this substance helps to inhibit the formation of stones)
- Urine volume (to assess if someone is drinking enough fluids)
Additional tests that may be part of some kidney stone risk panels and/or requested separately include:
- Urine cystine (or amino acid screen)
- Urine hosphorus (phosphate)
- Urine magnesium (helps to inhibit stone formation)
- Urine sodium (does not directly cause stones but affects the amount of calcium in urine and thus its ability to form stones)
A high concentration of one or more of these substances in the urine can occur when a person produces and excretes an excess amount of the substance. Other contributing factors include chronically not drinking enough fluids, becoming dehydrated to some degree, and having unusually concentrated urine.
For additional details, see the article on Kidney Stone Analysis.
How is the sample collected for testing?
A 24-hour urine collection is required for this test. Frequently, two different 24-hour urine samples are collected and tested to determine whether elevated levels of a substance are temporary or persistent.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
How is it used?
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 a first stone occurrence if a person is considered to be at high 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 (protein, red and white blood cells, pH, and presence of crystals or bacteria)
- Blood tests such as a urea) and creatinine to evaluate kidney function, electrolytes (sodium, potassium, chloride, bicarbonate) and calcium, to evaluate the body’s handling of these substances, especially when compared to urine results.
- A urine culture if a person shows signs of a urinary tract infection
- If a kidney stone is collected during surgery or if it passes on its own, kidney stone analysis is often performed to evaluate the specific substances present in it.
When is it requested?
A kidney stone risk panel is usually performed several weeks after treatment for a kidney stone has finished and is frequently run on two different 24-hour urine sample collections to determine whether elevated concentrations of a substance are temporary or persistent. In most cases, testing will be requested when a person has had at least two episodes of kidney stones, but it may be requested 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 or bilateral 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.
What does the test result mean?
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 either the blood or the urine, 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 changed their lifestyle or medication, decreasing concentrations of stone promoting substances and increasing levels of stone inhibiting substances represent a decreased risk of stone formation.
If a person is dehydrated, the amount of urine produced in 24-hours (urine volume) will be low and the urine will be concentrated. This can result in 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 form more easily 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 summarises what some test results may indicate:
Test Result Indicating Increased Kidney Stone Risk Stone Formation / Comments Creatinine N/A Blood and urine creatinine concentrations reflect kidney function; they may be used for comparing to other substances as the level of creatinine in blood is normally stable and, in urine, it reflects how dilute or concentrated the urine is. Urine calcium High Possibility for calcium oxalate or calcium phosphate stones Urine oxalate High Possibility for calcium oxalate stones Urine uric acid High Uric acid stones may form; many who have increased uric acid also have gout Urine citric acid (citrate) Low Citric acid helps inhibit stone formation by binding calcium
Other less common tests are summarized below:
Test Result Indicating Increased Kidney Stone Risk Stone Formation / Comments Urine cystine High Associated with inherited condition causing excess cystine in urine; additional testing may be performed to further evaluate. Urine phosphorus (phosphate) High Can contribute to calcium compound stone formation Urine magnesium Low Helps inhibit stone formation Urine sodium High Sodium can cause more calcium to be excreted into the urine, increasing the risk of calcium compound stones.
Is there anything else I should know?
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 urinary 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. It is referred to as ‘renal colic’.
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 stuck in 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. Conversely, some people will have normal results for the stone risk panel tests and yet form stones 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.
Should everyone have a kidney stone risk panel performed?
No, the test is not indicated as a general screening test and is not intended for people who have never had a kidney stone.
How can I prevent kidney stones?
One of the easiest things to do is to make sure that you stay hydrated by consistently drinking plenty of water. If you are at an increased risk of stones, your health care provider may recommend additional measures.
If I have had a kidney stone, should I avoid calcium?
You should work with your health care provider to determine the best treatment for you. If you have had a stone with calcium in it, you may be instructed to decrease your intake by a modest amount, but the clinical picture is often not as straight-forward as just consuming less calcium. Some people absorb extra calcium from their food, but some excess calcium in the urine is related to an excess of sodium, so people who have had calcium-containing stones are often told to decrease salt intake rather than reducing calcium intake. A drastic reduction in calcium can worsen stone formation as well as affect bone health.
Do I really need to save all of my urine for 24 hours?
Yes, your health care provider needs to know how much urine you are producing over a 24-hour period (volume) and how much of each of the substances is present. Since the substances may be eliminated in the urine at varying rates during the day and night, the 24-hour urine is a better representation than a single or random urine sample.
Is it necessary to do both blood and urine tests?
That will depend on the information that your health care provider wants to evaluate. It is common to compare some substances in both the blood and the urine.
Can stones form in other parts of the urinary tract besides the kidney?
Yes. For example, stones can form in the bladder; however, the reason for and the mechanism by which they form are different than for kidney stones. Instead of causes related to excreting excess amounts of a particular substance, bladder stones are typically caused by an inability to completely empty the bladder during urination. A bladder stone may be caused by some underlying urinary tract problem such as lack of bladder control, enlarged prostate, or urinary tract infection.
On This Site
Tests: Kidney Stone Analysis, Calcium, Uric Acid, Creatinine, Chloride, Potassium, Sodium, Magnesium, Phosphorus (phosphate), Electrolytes, Urea, Urinalysis, Albumin, Microalbumin, PTH, Cystine
Conditions: Kidney Disease, Urinary Tract Infection
Elsewhere On The Web
British Association of Urological Surgeons advice about kidney stones
Great Ormond Street Hospital: kidney stones in children
Renal Association information about cystinuria
BBC news article about dehydration and risk of stones