At a glance

Also known as

Urinary Stone Analysis; Calculus Analysis

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?

When a stone has passed through or been removed from your urinary tract

Sample required?

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

Test preparation needed?

None

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.

Normal urinary tract

                         Normal Urinary Tract
Source: National Institute of Diabetes and Digestive and Kidney Diseases

Kidney stones are one of the most common urinary tract disorders. The 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 in other parts of the urinary tract. They 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 abrupt, extremely severe pain that may be intermittent or continuous.

urinary tract stones

        Stones in the urinary tract 

Source: National Institute of Diabetes and Digestive and Kidney Diseases

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 pulverises the stone in place using targeted shock waves. The smaller particles and fragments that remain can then pass through the urinary tract.

Stones develop for several reasons. Most often they occur when there is a high concentration of crystal-forming substances in the urine such as calcium and uric acid. This can happen when someone produces and excretes an excess amount of the substance. It can also occur when someone does not drink enough over a period of time and has more concentrated urine because there is less water in it. Depending on how much and what type of substance 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 on the substances in the urine causing it. It may be made of just 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 sulfa drugs

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., about half a million people go to the emergency room each year with kidney stones and about three million visit their doctor.

How is the sample collected for testing?

Small stones can be passed in the urine and it's possible to collect them at home. Your doctor or pathology collection centre will provide you with a clean container and a straining device that has a fine mesh. You will need to filter all of your urine because there is no way to determine exactly when a stone will pass out of the body. You will be asked to examine 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 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 filter 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 to a laboratory for analysis.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

How is it used?

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, colour and texture. Often, a picture of the stone will be taken to document its size and appearance. The stone may also be cut into pieces in the laboratory so that its layers can be observed. One or more tests will then be performed to determine the stone's composition.

Blood, urine, and 24-hour urine tests are often ordered when someone has a suspected kidney stone. They are performed to detect excess chemicals that are being produced and excreted in the urine and to evaluate the person's health status. 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:

  • Blood and 24-hour urine tests for calciumuric acidcreatinine, and sometimes oxalate, citrate, phosphate, and/or cystine
  • Urinalysis - to detect red and white blood cells, crystals, signs of infection, and to measure urine pH
  • Full Blood Count (FBC) - to evaluate white blood cells for signs of infection

When is it requested?

Kidney stone analysis is ordered when someone has passed a kidney stone and it has been filtered out of the urine or when a stone has been surgically removed from the urinary tract.

Signs and symptoms associated with a kidney stone may lead a doctor to search for a stone either in voided urine or within the body using imaging tests. A doctor 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
  • Abdominal pain
  • Nausea and vomiting
  • Bloody and/or cloudy urine
  • Frequent urge to urinate
  • Fever and chills, when an infection is present

When someone has recurrent stones, not every stone may be tested. The first stone found will be tested and subsequent stones analysed as the doctor deems necessary.

What does the test result mean?

The chemical composition of the stone can usually be identified. This shows what the stone is made of, but it does not give the reason why the stone formed.

Someone may have an underlying disease or condition that causes them to produce and/or excrete an excess of a specific chemical into the urine. They may be inadequately hydrated and/or have acidic or alkaline urine that contributes to the crystallization process. Preventing kidney stone recurrence 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 they are 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—increased calcium or oxalate intake may result in increased excretion into 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.
    • Too much parathyroid hormone (primary hyperparathyroidism), leading to high serum and urine calcium.
    • A variety of metabolic disorders—these may lead to some degree of metabolic acidosis, resulting in an increased amount of calcium excreted in the urine.
  • Uric acid stone, then it is likely that they are producing and excreting excess uric acid due to conditions such as gout or disorders of uric acid metabolism.
  • Struvite stone, the person likely has a specific type of bacterial infection that leads to the production of excess ammonia.
  • Cystine stone, then the person is likely producing and excreting excess cystine as the result of a rare hereditary disorder.
  • Drug-related stone, then the person is forming stones because of a medication that they are taking.
  • Other stone, a variety of stones may be formed when an excess chemical is present and/or when the urine is very concentrated, such as may occur with dehydration.

Is there anything else I should know?

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 for other reasons. Those who have one kidney stone are at an increased risk for stone recurrence.

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:

  • A family history of kidney stones
  • Presence of a urinary tract infection
  • Abnormalities in the structure of the kidneys and/or urinary tract; this may cause the flow of urine to be impeded and crystals to be deposited, leading to formation of stones.
  • Kidney disorders such as polycystic kidney disease, a condition characterised by the presence of numerous cysts in the kidney.

Common Questions

Do I really have to filter all of my urine for this test?

Yes, as long as you have a suspected stone and are instructed to do so by your doctor. Since it is impossible to determine when the stone will pass, it is important to screen all of the urine in order to find and send it for analysis.

Can I just test my blood or urine instead of the stone?

Blood and urine tests provide important information about your condition but they will not show exactly which chemical compounds constitute the stone. The more information your doctor has, the better the chance they can help you prevent stone recurrence.

How bad is the pain with kidney stones?

It depends on the stone and varies from person to person but it is often severe and must sometimes be treated with strong prescription pain medications. For most people, the pain is most intense when the stone is moving through the urinary tract system.

If I have had a kidney stone, should I avoid calcium?

You will need to work with your doctor to determine the best treatment for you. If you had a stone with calcium in it, you may be advised to decrease your intake by a modest amount but the clinical picture is often less black and white and it's not simply a matter of taking more or less. Some people absorb extra calcium from their food, but sometimes excess calcium in the urine is linked to an excess of sodium, so people who have had calcium-containing stones are often told to decrease salt intake rather than reducing calcium intake. Sometimes drastic reductions in calcium can worsen stone formation as well as affect bone health.

How does a doctor find a stone in my urinary tract?

Your doctor can use imaging tests to locate and evaluate a kidney stone. These tests can help determine whether a stone is likely to pass out of the body without medical intervention.

Who performs a kidney stone analysis?

This testing requires specialised equipment and expertise. It is not offered by every laboratory.

What can I do to prevent a kidney stone and prevent recurrence?

Not every stone can be prevented but the most helpful thing you can do is to drink a enough water to stay well hydrated. Other things you can do will depend on your specific circumstances.


Last Review Date: February 7, 2016