A kidney stone analysis is performed to determine the chemical composition of a stone when it is filtered out of the urine or removed from the urinary tract. A laboratory will typically document the physical characteristics of a stone – its size, shape, weight, color and texture. Often, a picture of the stone will be taken to document its size and appearance. The stone may also be fractured so that its layers can be observed. One or more tests will then be performed to determine the stone's composition.
In addition to the stone analysis, blood, urine, and 24-hour urine tests are often ordered to determine whether the individual produces excess chemicals that may contribute to the formation of kidney stones and to evaluate the person's overall health. The test results can help distinguish between a probable stone and other conditions that may have similar symptoms but require different treatment. Testing may include:
Kidney stone analysis is ordered when a person has passed a kidney stone and it has been filtered out of the urine or when a stone has been removed from some part of the urinary tract.
Signs and symptoms associated with a kidney stone may lead a health practitioner to search for a stone either in voided urine or within the body using imaging tests. A health practitioner may suspect the presence of a stone when someone has:
Severe pain in the side of the back that may move to the groin (pain is the primary symptom of a kidney stone)
Nausea and vomiting
Bloody and/or cloudy urine
Frequent urge to urinate
Fever and chills, when an infection is present
When a person has recurrent stones, the first stone found would be tested. Subsequent stones would be analyzed as the health practitioner deems necessary.
A kidney stone analysis identifies the chemical composition of the stone. Common types of kidney stones include:
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 sulfa drugs
However, stone analysis does not give the reason that the stone formed.
A person with an underlying disease or condition may produce and/or excrete an excess of a specific chemical into the urine. Not drinking enough fluids and/or having urine with a high or low pH can contribute to a person's risk of forming stones. Preventing kidney stones from developing again depends upon identifying and addressing the cause of stone formation.
In general, if a person has a:
Calcium oxalate or calcium phosphate stone, then it is likely that the person is excreting excess calcium and/or oxalate (or sometimes too little citrate, which normally binds calcium but does not form stones) into the urine. This may be due to:
An inherited tendency to absorb more than the normal amount of calcium from the diet, causing high urine calcium (hypercalcuria).
Dietary factors—consuming food or drink high in calcium or oxalate may result in increased amounts of these substances in the urine.
Factors affecting absorption of nutrients, such as inflammatory bowel disease or intestinal surgery—an imbalance in nutrient absorption may result in excess urinary calcium.
Not everyone who drinks too little liquid or who has an excess amount of chemical in their urine will form kidney stones. Some stones will form in people for other reasons. Those who have had one kidney stone are at an increased risk for developing additional stones.
Several factors other than an excess of certain chemicals in the urine can contribute to the formation or increased risk of kidney stones. Some of these include:
This article was last reviewed on March 31, 2015. | This article was last modified on March 31, 2015.
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