To help determine the underlying reason for developing a kidney stone; to help guide and monitor treatment; to determine the risk of developing more stones.
Kidney Stone Risk Panel
When you have had two or more kidney stones and a healthcare professional wants to evaluate your risk of developing additional kidney stones; when you have developed one kidney stone and have a high risk of developing more stones; 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, uric acid or mixtures of these. Cystine stones are less common.
Kidney stones can form for several reasons, but the most common is because the person does not drink enough water and the urine is very concentrated. Often 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 phosphorus (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/or excretes an excess amount of the substance. Also, urine will be generally concentrated if the person is chronically dehydrated (not drinking enough fluids).
For additional details, see the article on Kidney Stone Analysis.
How is it used?
A kidney stone risk panel is used to identify biochemical risk factors for the development of more stones in someone who has already had at least one stone in their urinary tract. Testing is particularly important for people already at high risk for forming more stones or for people who are likely to develop kidney damage with further stones.
This testing can be used to help guide and monitor treatment to prevent the formation of further kidney stones.
Several other laboratory tests may also be used to help evaluate a person who has had a kidney stone, including:
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 separate 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 high risk of further stone formation or kidney damage. This may include people who:
- Formed stones as a child or young adult
- Have a family history of kidney stones
- Had multiple or bilateral kidney stones when they were first diagnosed
- Have a single functional kidney, including those who have had a kidney transplant
Sometimes testing is performed to monitor treatment, including when a person has made changes to their lifestyle (such as recommended dietary changes or drinking more water) or been given medication.
What does the test result mean?
The results of the kidney stone risk panel are evaluated along with other risk factors to determine a person's 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 may need further investigation to determine the cause.
Test results, however, cannot predict who will actually develop another kidney stone or when. Some people with mild elevations (or even results within normal ranges) will 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 (often mixed with calcium) and are associated with bacterial urinary tract 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 Likely to form calcium oxalate or calcium phosphate stones Urine oxalate High Likely to form calcium oxalate stones Urine uric acid High Likely to form uric acid stones; some people who have increased uric acid also have gout Urine citric acid (citrate) Low Citric acid helps prevent 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 Likely to be an inherited condition (cystinuria) causing cystine stones Urine phosphorus (phosphate) High Can contribute to calcium compound stone formation Urine magnesium Low Magnesium is thought to 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. Stones can cause problems either because they grow large enough to obstruct urine flow in a kidney or because they become dislodged or break off and begin to travel from a kidney through the ureter. They can stretch, irritate and damage the walls of the ureter and can cause temporary obstruction. Movement of a stone often causes 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 water 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 increased risk of forming another.
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.
Should everyone have a kidney stone risk panel performed?
How can I prevent kidney stones?
If I have had a kidney stone, should I avoid calcium?
You should work with your healthcare professional unless you have an unusual diet, avoiding calcium-containing foods does not help to prevent further stones and can actually increase stone formation and also cause bone problems. Some people absorb too much calcium from their food, but excess calcium in the urine is more often related to an excess of sodium, so people who have had calcium-containing stones are usually advised to decrease salt intake rather than reduce calcium intake.
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?
Can stones form in other parts of the urinary tract besides the kidney?
Yes. For example, stones can form in the bladder and are typically caused by an inability to completely empty the bladder during urination. This is often due to an underlying urinary tract problem such as lack of bladder control, enlarged prostate, or urinary tract infection. Bladder stones are less often caused by excess amounts of particular substances in the urine compared with kidney stones.
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