Also Known As
Urinary Stone Analysis
Calculus Analysis
Renal Stone Analysis
Formal Name
Kidney Stone Analysis
This article was last reviewed on
This article waslast modified on 30 September 2018.
At a Glance
Why Get Tested?

Finding out what a kidney stone is made of can help to determine the underlying cause and guide treatment to prevent further stones forming

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

On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

Kidney stone analysis involves testing the stone(s) to determine its composition. This helps to identify the cause of the stone and may help to prevent the formation of more stones.

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 and begin to travel from a kidney along the ureter. They can cause temporary obstruction and stretch, irritate, and damage the walls of the ureters. This movement often causes 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 cannot pass from the kidney into the ureters, and for smaller stones that get stuck in 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 fragments that remain can then pass through the urinary tract.

Stones can develop for many 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 if the urine is concentrated throughout the day because of a low fluid intake. It can also happen when a person produces and excretes an excess amount of the substance. 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 compounds 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 (or mixtures of these) make up about 95% to 99% of kidney stones. About 75% of stones will contain calcium. Less common stones include:

  • Cystine - stones produced because of an inherited condition that results in loss of cystine into the urine
  • Drug-related - stones that are caused by crystallisation of 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.

How is the sample collected for testing?

Most stones are collected during a surgical operation, in which case the hospital staff will send any material for testing.

If an operation is not required, you may be asked to pass urine through a small sieve for a few days to catch any stones that pass naturally. This is necessary because there is no way to determine exactly when a stone will pass out of the body. Bearing in mind that stones may be as small as grains of sand, any particles or obvious stones should be placed into a clean container provided by the doctor and then returned to the laboratory. It is important not to add anything to the stone, such as tissue or tape, as this can make testing more difficult.

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

No test preparation is needed.

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Common Questions
  • How is it used?

    Kidney stone analysis is performed to determine the chemical composition of a stone after it has been filtered out of the urine or removed from the urinary tract. A laboratory will typically note the physical characteristics of a stone – its size, shape, weight, colour and texture. Sometimes, a picture of the stone will be taken to document its size and appearance. The stone may also be broken so that its layers can be seen. One or more tests will then be performed on crushed fragments to determine the stone's composition.

    Blood, urine, and 24-hour urine tests are often requested when a person has a suspected kidney stone. They are performed to detect an underlying cause for stone formation such as excess chemical substances being produced and excreted in the urine. Testing may include:

  • When is it requested?

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

    Signs and symptoms associated with a kidney stone may lead a doctor to search for a stone either in urine or within the body using X-rays or scans. A doctor may suspect the presence of a stone when someone has:

    When a person has recurrent stones, the first stone found is often tested. Subsequent stones would be analysed only if the doctor deems necessary.

    • Severe pain in the side of the back that may move to the groin; pain is the commonest symptom of a kidney stone
    • Abdominal pain
    • Nausea and vomiting
    • Bloody and/or cloudy urine
    • Frequent urge to urinate
    • Fever and chills, when a urinary infection is present

    When a person has recurrent stones, the first stone found is often tested. Subsequent stones would be analysed only if the doctor deems necessary.

  • What does the test result mean?

    The chemical composition of the stone can usually be identified. This tells the doctor what the stone is made of, but may not give the cause of stone formation. A person 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 have concentrated urine indicating that they do not drink enough clear fluids. They may also have acidic or alkaline urine that contributes to the formation of crystals. Preventing kidney stone recurrence depends upon identifying and addressing the cause of stone formation.

    • Calcium oxalate or calcium phosphate stones form when there is excess calcium and/or oxalate (or sometimes too little citrate, which normally binds calcium to prevent stones) in the urine. This may be due to:
      • Diet - eating too much animal protein, sugar, salt or foods rich in oxalate increases the risk of stone formation by altering the chemical balance of the urine. High salt intake can lead to increased excretion of calcium into the urine.
      • An inherited tendency to absorb more than the normal amount of calcium from the diet, causing high urine calcium (hypercalcuria).
      • Factors affecting absorption of nutrients, such as inflammatory bowel disease or intestinal surgery - an imbalance in nutrient absorption may result in excess urinary oxalate.
      • Too much parathyroid hormone (primary hyperparathyroidism), leading to high blood and urine calcium.
      • A variety of metabolic disorders—these may lead to some degree of metabolic acidosis, resulting in high urine calcium excretion.
    • Uric acid stones form when the urine is persistently acidic or when there is excess uric acid such as occurs with gout. People with diabetes are more likely to develop uric acid stones.
    • Struvite stones form when specific types of bacteria infect the urine and produce ammonia.
    • Cystine stones occur in people with a rare inherited disorder in which excess cystine is excreted in the urine.
    • Drug-related stones (very rare) form when certain drugs crystalise in the urinary tract, especially if they are taken for a long time or in very high doses.
  • Is there anything else I should know?

    Not everyone who drinks too little liquid or who has an excess amount of a substance 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 of developing further stones.

    Several other factors 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 disturb the flow of urine so that crystals form; these can grow into stones.
    • Kidney disorders such as polycystic kidney disease, a condition characterised by the presence of numerous cysts in the kidney.
  • 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 know when the stone will pass, it is important to screen all of the urine in order to catch it and send it for analysis.

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

    Blood and urine can give your doctor important information about your condition, but they will not tell the doctor exactly which chemical compounds constitute the stone. The more information your doctor has, the better the chance that he or she can help you prevent more stones forming.

  • How bad is the pain with kidney stones?

    It depends upon the stone and will vary 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 system.

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

    You should work with your doctor to determine the best treatment for you. Eating a diet that is naturally rich in calcium rarely causes kidney stones and protects your bones. About half a pint of milk a day or the equivalent in other dairy products, such as yoghurt or cheese, is about right. In some people, a drastic reduction in calcium in the diet can worsen stone formation as well as weaken bones. Reducing the amount of salt in the diet reduces the risk of stones by its effect on calcium excretion and has the added benefit of lowering blood pressure. It is therefore much more beneficial to avoid salt than calcium. Calcium that is taken in the form of supplements that are prescribed or bought from a pharmacy can increase the risk of producing stones. If you are taking such supplements and have had kidney stones, you should discuss this with your doctor.

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

    The doctor can use imaging tests (X-rays, CT scans, ultrasound scans) 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. In most cases, your stone will be sent to a reference laboratory.

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

    Not every stone can be prevented, but the most helpful actions are to drink a sufficient amount of water to remain well hydrated and to reduce salt and animal proteins in the diet. Other actions will depend upon your specific circumstances.

  • What are some of the specific methods used to analyse kidney stones?

    Common methods of kidney stone analysis include infrared spectroscopy and X-ray diffractometry.

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