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Kidney Stone Analysis

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Also known as: Urinary Stone Analysis; Renal Calculus Analysis
Formal name: Kidney Stone Analysis
Related tests: Urinalysis, Kidney Stone Risk Panel, Uric Acid, Calcium, Phosphorus, Creatinine, Oxalate, Citrate, Cystine

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The Test Sample

What is being tested?

Kidney stones are small, hard masses that form within the kidneys. Kidney stone analysis uses one or more test methods to examine and determine the composition of a stone. This is done in order to help identify the cause of the stone and, where possible, to prevent the formation of more stones.

Thumbnail diagram showing kidney stones in urinary tractThumbnail diagram of normal urinary tractThe kidneys are part of the urinary tract, which also consists of two ureters, the bladder, and the urethra. The kidneys filter waste out of the blood and produce urine, which is transported from the kidneys to the bladder through tube-like ureters. Urine is eliminated from the bladder through the urethra. This is a continual process of waste filtration, urine production, and elimination.

Commonly called kidney stones, calculi can form in the kidneys and 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; they can cause temporary obstruction and stretch, irritate, and/or damage the walls of the ureters. 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. The stone may need to be surgically removed, often using devices that pass through the urethra and bladder to the site of the stone. With some stones, it is possible to use extracorporeal shock wave lithotripsy. This treatment pulverizes the stone in place using targeted shock waves. The smaller particles and fragments that remain can then pass through the urinary tract.

Stones can develop for several reasons, but the most common is because there is a high concentration of a particular chemical in the urine that precipitates and forms crystals. This can happen when a person produces and excretes an excess amount of the chemical. It can also occur when a person chronically takes in little liquid and has more concentrated urine because there is less water in it. Depending on how much and what type of material crystallizes and where it forms, a kidney stone may be round, sharp and pointy or irregular with branches (called a staghorn). It can range in size from a grain of sand to bigger than a golf ball. The composition of the stone depends upon the chemicals present in excess. It may be all one chemical compound or have different chemicals in different layers.

According to the National Institute of Diabetes and Digestive and Kidney Diseases, kidney stones are one of the most common urinary tract disorders. In the U.S., more than 300,000 people go to the emergency room each year with kidney stones and about a million visit their healthcare provider.

How is the sample collected for testing?

The health practitioner or laboratory typically provides a person who has kidney stone symptoms with a clean container and a straining device that has a fine mesh. The person filters all of their urine through the fine mesh. This is necessary because there is no way to determine exactly when a stone will pass out of the body. The person then examines the mesh for any particulates, keeping in mind that stones may be easily visible or as small as grains of sand. If a stone is found, it is placed into the clean container, allowed to dry, and returned to the laboratory or healthcare provider as instructed. It is important not to add anything to the stone, such as tissue or tape, as this can make testing more difficult.

If a person is in a hospital, then medical personnel will filter the urine. With a kidney stone that is too large to pass, a health practitioner may perform a surgical procedure to remove it and then send the stone for analysis.

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.