Kidney stones | Kōwhatu tākihi

Kidney stones are solid crystals formed from the salts in your pee. They can be as small as a grain of sand or as big as a golf ball. They form in your kidney or in the tube that leads from your kidney to your bladder, known as the ureter.

Kidney stones can block the flow of pee and cause infection, kidney damage or even kidney failure. They can vary in size, location (where in the kidneys they are placed), types and colours. You can develop one kidney stone or several at the same time. How they are treated depends on what type of stone you have.

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(NHS, UK, 2021)

Dehydration (not making enough pee)

This is the most common cause of kidney stones. It often results from loss of body fluids from not drinking enough, especially when doing hard exercise, or working or living in a hot place. When pee volume is low, it is concentrated and dark in colour. Concentrated pee means there is less fluid to keep salts dissolved.

Increasing fluid intake dilutes salts in your pee. If you do this, you will reduce your risk of further stones. Adults who form kidney stones should drink enough fluid to make at least 2.5 litres of pee every day. This usually means drinking about 3 litres. Water is best to drink, but what matters most is getting enough fluid.

Diet

What you eat can also affect your chance of forming a kidney stone. Work with your healthcare provider to find out whether your diet is a factor. You may be eating foods that increase your risk of forming a stone or not eating enough of the foods that help prevent further stones.

Bowel conditions

Some bowel conditions that cause runny poos (such as Crohn’s disease or ulcerative colitis) or surgeries (such as gastric bypass surgery) can raise your risk of forming calcium oxalate stones.

This is because runny poos may cause you to lose large amounts of fluid from your body, reducing the amount you pee. Your body may also absorb excessive oxalate from your intestine, resulting in more oxalate in your pee. Both low pee volume and high levels of urine oxalate can cause calcium oxalate kidney stone formation.

Other factors

• Obesity may change the acid levels in your pee, leading to stone formation.
• Calcium and vitamin C supplements may increase your risk of forming stones.
• Medications used for treating some medical conditions, such as kidney disease, cancer or HIV, can also increase your risk of developing kidney stones.
• Having a close relative who has had a kidney stone increases your risk of getting kidney stones.

In many cases, stones can be present without causing any symptoms at all.

Pain is usually the first sign of a kidney stone. Stones that stay in your kidney can cause mild to moderate pain just below your ribs on the side. You usually have the most severe pain (known as renal colic) when the stone moves from your kidney into your ureter. 

Renal colic is usually sudden, may come and go, and can be extremely painful (excruciating). The pain usually starts in your back and spreads to your groin. If you also develop fevers or cold chills with shakes (rigors), this can be a serious infection and you must see a doctor or after hours clinic straight away.

Other symptoms are:

• blood in your pee
• cloudy or smelly pee
• peeing frequently
• pain when peeing
• difficulty peeing
• severe back or side pain (this can include belly or groin pain)
• nausea and vomiting
• fever or chills (if an infection is present).

Some kidney stones, called ‘silent’ kidney stones, cause no symptoms and are often found in an x-ray during a health check. Other people have their stones diagnosed when they get sudden pain while the stone is passing, and need medical attention.

If a stone passes out of your body, collect it and take it to your doctor. This can help them decide on your treatment. Urine and blood tests can also help to find the cause of your stone.

If you have blood in your pee or sudden abdominal or side pain, tests like an ultrasound or a CT scan may diagnose a stone. These imaging tests tell the healthcare provider how big the stone is and where it is located. A CT scan is often used in the emergency department when a stone is suspected. It is used because it can make a quick and exact diagnosis.

Most stones will pass out in your pee within 3–6 weeks without needing any treatment. During this time, you may experience renal colic (a gripping pain in your back) that will generally be treated with pain relief medicines from your GP or emergency clinic.

If the pain is controlled and your stone is known to be small, generally the best course of treatment is to wait for several days or weeks for the stone to pass into your bladder.

If, however, the stone is too large to pass or doesn’t pass with time, you will need treatment. The choice of which type of treatment is best for you will be made by your urologist, depending on many factors such as the size and position of the stone.

The treatment can be in one of the following forms:

• Ureteroscopy – a small, narrow ‘telescope’ is passed up through your bladder to the stone so that the stone can be removed or broken (sometimes with a laser).
• Lithotripsy– a special machine is used that sends ‘shock waves’ through your body to break up the stone into tiny pieces that will later pass in your pee.
• Percutaneous surgery – a telescope is passed through your skin on your back (and into your kidney) to see and remove the stone. This is reserved for stones that are large and still in a kidney.
• Open surgery – nowadays it is very rare to require a ‘cutting’ operation to remove a stone but it is sometimes the best option.

If you have had a kidney stone, you have an increased chance of getting a second stone. About 30–50% of people with a first kidney stone will get a second one within 5 years and then the risk reduces. However, some people keep getting stones their whole lives. Here are some things you can do to reduce your risk of getting kidney stones.

Drink plenty of water

The most important thing you can do to prevent further kidney stones forming is to drink lots of fluid. Drink at least 2–2.5 litres of fluid each day. Drink throughout the day and night if possible. The best fluid is water. You will know if you are drinking enough by the colour of your urine, which should be pale yellow to clear.

Cut down on salt

Reduce salt (sodium) intake by keeping salt in cooking to a minimum and not adding it to meals. Reducing salt lowers your risk of calcium-containing stones. Choose low- or no-salt processed foods.

Check with your doctor whether to cut back your calcium intake

Only reduce your intake of calcium-containing foods, including milk, yoghurt and cheese, if your doctor tells you to. Reducing calcium in your diet might increase your risk of weak bones and osteoporosis. For adults the recommended daily allowance is approximately 800 milligrams. You can meet this by eating 3–4 small to moderate servings of milk and dairy foods a day (eg, one serve = a pottle of yoghurt or a glass of milk).

Ask your doctor about any other restrictions

You will be informed by your health professional if further dietary restrictions such as limiting oxalate-containing foods are required.

Ask your pharmacist or doctor about your medicines

Some medicines may increase your risk of kidney stones. However, don’t stop your medications without talking to your doctor. If you are taking any prescription medicines or herbal, vitamin or dietary supplements, check with your doctor or pharmacist whether these medicines increase your risk of forming stones.