A kidney stone is a solid mass made up of tiny crystals that form within the kidney or urinary tract. Over time, the crystals may build up to form a hard stone-like lump. The stone can range in size from just a speck to as large as a golf ball.
Kidney stones can cause severe pain and a range of other symptoms, depending on the size of the stones. Small kidney stones can cause pain as they pass through the urinary tract. Large kidney stones can become stuck in the kidney, ureter or bladder, causing pain and blockage of urine flow. This can lead to infection and kidney damage.
Kidney stones are one of the most common disorders affecting the urinary tract worldwide. According to the National Institute of Health (NIH), over 10 million people are found to have kidney stones yearly. Once you have one stone, you are more likely to have another, unless measures are taken to prevent stone formation. Kidney stones are more common in men than in women. And, while they can occur at any age, kidney stones are more likely to occur in people aged over 30 and continues to rise until age 70.
Types of Kidney Stones
Depending on the main cause of formation, kidney stones can be categorized into four different types:
- Calcium stones
These are the most common type of kidney stones. They are composed of calcium in combination with either oxalate or phosphate. These occur when there are excess levels of calcium in the urine.
- Uric acid stones
These kidney stones occur when excess amounts of uric acid are present in the urine. Approximately 50 percent of people with this type of kidney stones also develop gout – a painful form of arthritis caused by solid deposits of uric acid in the joints.
- Struvite stones
These kidney stones are often composed of magnesium ammonium phosphate and tend to occur in women who have recurrent urinary tract infections. This type of kidney stone can grow very large and can block the kidney, ureter, or bladder.
- Cystine stones
These kidney stones form in people with a hereditary disorder that causes the kidneys to excrete too much of the amino acid, called cystine. This type of kidney stone is rare and is caused by a relatively rare metabolic condition.
Causes of Kidney Stones
Kidney stones form when your urine contains high levels of substances such as calcium, oxalate, or uric acid. This is more likely to happen if you don’t drink enough fluids or if you have certain medical conditions and metabolic imbalances that raise the levels of certain substances in your urine.
Other factors that can increase the risk of developing kidney stones include:
- Family history of kidney stones.
- Taking some medications, such as diuretics and corticosteroids.
- Excess vitamin D intake.
- Having certain medical conditions and metabolic problems such as hyperparathyroidism, urinary tract infections, Crohn’s disease, sarcoidosis and some cancers.
Symptoms of Kidney Stones
If you have kidney stones that are very small, they are unlikely to cause symptoms and are passed painlessly in your urine. These stones are referred to as “silent stones”. Symptoms usually occur if the kidney stone starts to travel down the ureter (tube that connects the kidney to the bladder). At that point, you may experience these signs and symptoms:
- Intense pain in the lower back or side of your abdomen.
- Persistent need to urinate.
- Burning sensation when passing urine.
- Nausea and vomiting.
- Cloudy or smelly urine.
- Fever and chills (if there is an infection).
- Blood in urine (hematuria) – this may be caused by the stone scratching the kidney or ureter.
Diagnosis of Kidney Stones
To diagnose kidney stones, a doctor will do a physical exam and ask about your medical history. The doctor may ask if you have a family history of kidney stones and about your diet. The doctor may perform urine, blood, and imaging tests to complete the diagnosis.
Once a diagnosis of kidney stones has been made, referral to a specialist urologist for further assessment may be recommended. Occasionally, the specialist may request to perform a CT scan or a special X-ray using contrast dye (an intravenous urogram) to accurately identify the size and location of the kidney stones.
Treatments for Kidney Stones
The treatment for kidney stones usually depends on the size and location of the stones. In the majority of cases, smaller kidney stones will pass by themselves. In these cases, the only treatment required is drink plenty of fluids and rest. Medications may be given to relax the ureter, allowing the kidney stones to pass more quickly and with less pain.
If you have a large kidney stone or if the stone is not passed on its own, the urologist may use the following treatments to break up, remove, or bypass kidney stones.
Shock Wave Lithotripsy (SWL). The urologist may use a shock wave machine to crush the kidney stone. The shock waves go from the machine to your body. The smaller pieces of the stone then pass through your urinary tract.
Ureteroscopy. The urologist uses a long, tube-like tool with an eyepiece, called an ureteroscope, to find the stone. The tool is fed into the urethra and through the bladder to the ureter. Once the stone is found, the urologist can remove it or can break it into smaller pieces with laser energy.
Percutaneous nephrolithotomy. The urologist uses a wire-thin viewing tool, called a nephroscope, to locate and remove the stone. The tool is fed directly into the kidney through a small cut made in your back. For larger stones, shock waves may also be used to break the stone into smaller pieces.
How to Prevent Kidney Stones
Since the risk of having a kidney stone is increased if you have previously had one, prevention is very important. The best way to prevent kidney stones is to drink plenty of water each day to avoid becoming dehydrated. Normally, a person should drink at least six to eight glasses of water a day, but people who have had a kidney stone before are encouraged to increase their fluid intake to 2-3 three liters a day.
Drinks such as coffee, tea, and fruit juice can count towards your fluid intake, but water is the healthiest option for preventing kidney stones from developing.
Keeping your urine diluted helps to stop waste products getting too concentrated and forming stones. You can tell how diluted your urine is by looking at its colour. The clear your urine is, the less concentrated it is.
You should also make sure you drink more when you’re exercising to replenish fluids lost through sweating.
Depending on the type of stone involved, your doctor may advise you to eat less of certain kinds of foods. For example, if your kidney stone is caused by too much calcium, you may be advised to reduce the amount of oxalates in your diet. Oxalates prevent calcium being absorbed by your body, and can accumulate in your kidney to form a stone.
Foods that contain oxalates include:
- Coffee or tea
- Soy products
To avoid developing a uric acid stone, you should reduce the amount of protein and sodium in your diet.
Doctors may also prescribe medicines to prevent kidney stones to form. The type of medication prescribed will depend on the type of stone the person has previously experienced.