What is being tested?

Kidney stones are small, hard deposits made of minerals and salts that form within the kidneys, they are one of the most common urinary tract disorders. 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.

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 stone is broken into very small fragments that can pass through the urinary tract.

Stones develop for several reasons. Most often they occur when there is a high concentration of a particular chemical substance in the urine that precipitates and forms crystals. 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 chemicals present in excess. 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 Kidney Health Australia about 4% to 8% of Australians suffer from kidney stones at some time.

How is it used?

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 an underlying cause for stone formation such as excess chemical substances being produced and excreted in the urine.  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 calcium, uric acid, creatinine, 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 such as X-rays or CT scans. 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 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 (hypercalciuria).
• Dietary factors—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.
• 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 serum and urine calcium.
• A variety of metabolic disorders—these may lead to some degree of metabolic acidosis, resulting in an increased high urine calcium excretion.

• 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. Eatiing a diet that is naturally rich i calcium rarel causes kidney stones and protects your bones. 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 a doctor find a stone in my urinary tract?

Your doctor can use imaging tests (X-rays, CT scans, ultrasounds) 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 and 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 thing you can do is to drink a enough water to stay well hydrated. Reduce the amount of salt and animal protein in your diet. Other things you can do will depend on your specific circumstances.