What are kidney stones?
Kidney stones, or renal calculi, are solid masses made of crystals. Kidney stones usually originate in your kidneys. However, they can develop anywhere along your urinary tract, which consists of these parts:
Kidney stones are one of the most painful medical conditions. The causes of kidney stones vary according to the type of stone.
Types of kidney stones
Not all kidney stones are made up of the same crystals. The different types of kidney stones include:
Calcium stones are the most common. They’re often made of calcium oxalate (though they can consist of calcium phosphate or maleate). Eating fewer oxalate-rich foods can reduce your risk of developing this type of stone. High-oxalate foods include:
However, even though some kidney stones are made of calcium, getting enough calcium in your diet can prevent stones from forming.
This type of kidney stone is more common in men than in women. They can occur in people with gout or those going through chemotherapy. This type of stone develops when urine is too acidic. A diet rich in purines can increase urine’s acidic level. Purine is a colorless substance in animal proteins, such as fish, shellfish, and meats.
This type of stone is found mostly in women with urinary tract infections (UTIs). These stones can be large and cause urinary obstruction. They result from a kidney infection. Treating an underlying infection can prevent the development of struvite stones.
Cystine stones are rare. They occur in both men and women who have the genetic disorder cystinuria. With this type of stone, cystine — an acid that occurs naturally in the body — leaks from the kidneys into the urine.
A kidney stone may not cause symptoms until it moves around within your kidney or passes into your ureter — the tube connecting the kidney and bladder. At that point, you may experience these signs and symptoms:
Severe pain in the side and back, below the ribs
Pain that radiates to the lower abdomen and groin
Pain that comes in waves and fluctuates in intensity
Pain on urination
Pink, red or brown urine
Cloudy or foul-smelling urine
Nausea and vomiting
Persistent need to urinate
Urinating more often than usual
Fever and chills if an infection is present
Urinating small amounts
Pain caused by a kidney stone may change — for instance, shifting to a different location or increasing in intensity — as the stone moves through your urinary tract.
When to see a doctor
Make an appointment with your doctor if you have any signs and symptoms that worry you.
Seek immediate medical attention if you experience:
Pain so severe that you can't sit still or find a comfortable position
Pain accompanied by nausea and vomiting
Pain accompanied by fever and chills
Blood in your urine
Difficulty passing urine
Kidney stones often have no definite, single cause, although several factors may increase your risk. Kidney stones form when your urine contains more crystal-forming substances — such as calcium, oxalate and uric acid — than the fluid in your urine can dilute. At the same time, your urine may lack substances that prevent crystals from sticking together, creating an ideal environment for kidney stones to form.
Risk factors for kidney stones
The greatest risk factor for kidney stones is making less than one liter of urine per day. This is why kidney stones are common in premature infants who have kidney problems. However, kidney stones are most likely to occur in people between the ages of 20 and 50.
Different factors can increase your risk of developing a stone. Typically, Caucasians are more likely to have kidney stones than those of African descent.
Sex also plays a role. More men than women develop kidney stones, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).
A history of kidney stones can increase your risk. So does a family history of kidney stones.
Other risk factors include:
a diet with high levels of protein, salt, or glucose
gastric bypass surgery
inflammatory bowel diseases that increase calcium absorption
taking medications such as diuretics, antiseizure drugs, and calcium-based antacids
The best way of preventing kidney stones is to make sure you drink plenty of water each day to avoid becoming dehydrated.
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 darker your urine is, the more concentrated it is.
Your urine is usually a dark yellow colour in the morning because it contains a build-up of waste products that your body has produced overnight.
Drinks such as tea, coffee and fruit juice can count towards your fluid intake, but water is the healthiest option and is best for preventing kidney stones developing.
You should also make sure you drink more when it's hot or when you're exercising, to replenish fluids lost through sweating.
Read more about preventing dehydration.
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:
almonds, peanuts and cashew nuts
grains, such as oatmeal, wheat germ and wholewheat
Don't reduce the amount of calcium in your diet unless your GP advises you to. This is because calcium is very important for maintaining healthy bones and teeth.
To avoid developing a uric acid stone, you should reduce the amount of meat, poultry and fish in your diet. You may also be prescribed medication to change the levels of acid or alkaline in your urine.
If you have a kidney stone, medication will usually be prescribed for pain relief or to prevent infections developing.
However, some medication may need to be reviewed by your GP if it's thought to be causing your kidney stone. The type of medication your GP prescribes will depend on the type of kidney stone you have.
For example, if you have:
calcium stones – you may be prescribed a diuretic medication if they are caused by hypercalcuria (an inherited condition)
struvite stones – you may be prescribed antibiotics to help prevent a urinary tract infection or kidney infection, which are the main causes of struvite stones
uric acid stones – you may be prescribed allopurinol (a medication used to lower uric acid levels) and medication to help alkalise your urine
cystine stones – you may be prescribed medication to lower levels of cystine in your urine.