The Test Sample
What is being tested?
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 level of one 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
- 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 inhibit the formation of stones)
Additional tests that may be part of some kidney stone risk panels and/or ordered separately include:
- Urine cystine
- Urine phosphorus
- Urine magnesium (helps 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 drinking an inadequate amount of 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.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.