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Kidney stones

Dr Karen Martin
Reviewed by Dr Karen MartinReviewed on 19.10.2023 | 5 minutes read
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Kidney stones are crystals formed from the naturally occurring salts in urine that bulk together to form a solid lump. Waste products in the blood can occasionally form crystals that collect inside the kidneys. Stones can develop in one or both kidneys. The medical name for stones in the kidneys is nephrolithiasis, and if the stones cause severe pain, this is known as renal colic. About 2% of adults have a kidney stone at any one time and it usually affects people aged 30–60 years of age. Renal colic affects about 10–20% of men and 3–5% of women. There is often no obvious reason why stones occur.

Symptoms vary widely and people often have kidney stones without realizing it, suffering no symptoms. Stones may cause pain when they are stationary in the kidney itself, but the real problems occur if they move out from the kidney and into the pipe connecting the kidney and bladder (the ureter). If this happens, along with causing severe pain, they can block the pipe, leading to potential infection and difficulty passing urine. This may prevent the kidneys from working effectively, with immediate or long term consequences. Pain may be felt in the side of the abdomen and down into the groin area, severe enough to cause vomiting, sweating and profound agitation. There may be blood in the urine and a need to urinate frequently, and symptoms can last from minutes to days. The size of the stone passed need not match the symptoms felt since a tiny stone the size of a grain of sand can be enough to trigger severe pain.

If you have classical-sounding pain, along with blood in your urine, your doctor may arrange a scan to see whether there is any evidence of kidney stones.

What causes the stones?

Kidney stones form because there is an imbalance in certain chemicals produced in your urine, such as calcium. This can be due to a medical problem or certain regular medications.

Stones are more likely if you are dehydrated or don’t drink enough fluids, as this dilutes the stone-forming chemicals, to be passed out in the urine. Medical textbooks sometimes describe a typical kidney stone patient being a middle-aged chef who works in a hot environment and doesn’t drink enough water during a busy evening of work. The moral of that story is to carry your water bottle and stay hydrated.

When should I see a doctor?

If you think you have a kidney stone, you will need to see or speak to your doctor. You may be looking for some pain relief, and if it is the first time you have had a suspected kidney stone, then you will need some sort of imaging to confirm the diagnosis. Scans can include X-rays, ultrasound, and CT scans.

If you have had kidney stones before and have spoken to your doctor about managing them at home if the pain is controlled, you should know when you may need to escalate things.

If you get a fever, you should immediately go to the emergency department, as this can indicate a blocked and infected kidney due to the stone. If you are unable to pass urine for several hours, you should go to the emergency department urgently.

If you don’t notice the stone pass, you will need to see your doctor to arrange some imaging to check that the stone has passed and is not stuck and potentially causing long-term kidney damage by blocking the tube connecting the kidney and bladder.

Your doctor will, of course, consider other causes of tummy pain, including a urine or kidney infection, appendicitis, pelvic inflammatory disease in women or prostatitis in men, or simple severe lower back pain.

How is it treated?

In many cases, no treatment is needed to pass kidney stones. Even stone sizes up to around half a centimeter in diameter can pass out by themselves. They can be painful, so pain relief may be the only thing required to help get through it. You can take acetaminophen or ibuprofen (if just for short-term relief). Any stronger pain relief can be prescribed by your doctor.

If the stone is large, or there are other complications such as infection or damage to the kidney and its filtering effects, then other treatments may be required.

These include shock wave therapy to break up stones that are still in the kidney. Operations can include collecting and removing stones from the kidney or ureter.

In emergency situations, when stones get stuck and completely block the ureter, a stent can be placed to keep the person safe in the short term. A stent is a tube that is passed from the bladder to the kidney to ensure no blockage or complications occur due to the stone, and urine can pass freely down the ureter and around the stone due to the presence of the stent.

How can I prevent kidney stones?

Over half of all people who have had one stone go on to develop another within 10 years so it is very important for people who have a tendency to form these to drink lots of fluid each day, with the aim of keeping the urine as dilute as possible. This should be of the order of at least 100 ounces (3 liters) of water a day, and if it is hot this will need to be increased further. You can tell how diluted your urine is by looking at its color. The darker your urine is, the more concentrated it is. In the less common cases where there is an underlying cause for stones forming, dietary advice or medication may help along with specialist assessment in rarer conditions.

If your kidney stone is caused by an excess of calcium, you may be advised to reduce the amount of oxalates in your diet. Oxalates prevent calcium from being absorbed by your body, and can accumulate in your kidney to form a stone. Foods that contain oxalates include beetroot, asparagus, rhubarb, chocolate, berries, leeks, parsley, celery, almonds, peanuts and cashew nuts, soy products and grains, such as oatmeal and wheat germ.

If you take regular medications, you can speak to your doctor to check that none of the medications could be linked to kidney stone formation. You should also avoid drinking excessive amounts of tea, coffee, salt, fizzy drinks and beer which can predispose to certain types of stone formation.

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This article has been written by UK-based doctors and pharmacists, so some advice may not apply to US users and some suggested treatments may not be available. For more information, please see our T&Cs.
Dr Karen Martin
Reviewed by Dr Karen Martin
Reviewed on 19.10.2023
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