Kidney Stone Analysis

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

At a Glance

Why Get Tested?

To evaluate the composition of a kidney stone, to help determine the cause of its formation and to guide treatment

When to Get Tested?

A stone can be analysed either after a surgeon has removed it from your urinary tract or if you catch a stone that has come out of your urinary tract when passing urine

Sample Required?

A stone filtered from your urine or surgically removed from your urinary tract by a doctor

Test Preparation Needed?

None

The Test Sample

What is being tested?

Kidney stone analysis uses one or more test methods to examine and determine the composition of a stone from the urinary tract. 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 tract

The urinary tract consists of two kidneys, two ureters, the bladder, and the urethra. The kidneys filter the blood to remove waste substances, which are excreted from the body in the urine. Urine is transported from the kidneys to the bladder through tube-like ureters and eliminated from the bladder through the urethra. This is a continual process of waste filtration, urine production, and elimination.

Kidney stones, also known as renal stones, urinary tract stones or calculi, can form in the kidneys and in other parts of the urinary tract. Kidney stones 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. They can cause temporary obstruction and stretch, irritate, and/or damage the walls of the ureters. This movement can cause sudden, extremely severe pain that may be intermittent or continuous (‘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 into but do not pass all the way 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 (cystoscope or ureteroscope). With some stones, it is possible to use extracorporeal shock wave lithotripsy. A beam of ultrasound shock waves from outside the body is focussed onto the stone, which breaks into smaller pieces. 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 substance in the urine that precipitates and forms crystals. This can happen when a person produces and excretes an excess amount of the substance. Crystals can also form if the urine is concentrated throughout the day because the person is not drinking much fluid. Depending on how much and what type of material crystallises 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.

Common types of kidney stones include:

  • Calcium oxalate
  • Calcium phosphate
  • Uric acid
  • Struvite (magnesium ammonium phosphate) - stones associated with a bacterial infection
  • These four types make up about 95% to 99% of kidney stones. About 75% of stones will contain calcium. Less common stones include:

  • Cystine - stones associated with an inherited excess of cystine excretion
  • Drug-related - stones that are associated with drugs such as guaifenesin, indinavir, triamterene, atazanavir, and sulfonamides.
  • In the UK, about one in ten people will have a urinary stone sometime in their lives. Men are more likely to have stones than women. People who have had a stone in the past are more likely to develop stones in the future.

    Kidney stone analysis uses one or more test methods to examine and determine the composition of a stone from the urinary tract. This is done in order to help identify the cause of the stone and, where possible, to prevent the formation of more stones.

    How is the sample collected for testing?

    The doctor or laboratory typically provides a person who has kidney stone symptoms with a clean container and a straining device that has a fine mesh (a small kitchen sieve is suitable). The person filters all of their urine through the sieve. 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 sieve for any particles, keeping in mind that stones may be 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 doctor 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 check the urine. With a kidney stone that is too large to pass, the doctor 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.

    The Test

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    NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.