Kidneys and kidney stones
Kidney stones (also called renal calculi, renal lithiasis, and nephrolithiasis) occur when chemicals and minerals, in the urine combine to form solid material inside the kidneys.
Kidney stones can vary in size from a grain of sand to bigger than a golf ball. They can be smooth or they can have jagged edges. Small kidney stones can cause pain as they pass through the urinary tract. Large 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.
A person can have a single stone or many of them.
What causes kidney stones?
There are several types of kidney stones, each the result of different causes or processes in the body.
- Calcium stones: These are the most common type of kidney stone. They are composed of calcium in combination with other chemicals. These occur when there are excess levels of calcium circulating in the blood. This may be due to medical conditions such as hyperthyroidism and sarcoidosis, or as the result of a diet high in meat, fish, and poultry
- Uric acid stones: These kidney stones occur when excess amounts of uric acid are present in the blood. They tend to occur in people who do not drink sufficient fluids or lose a lot of fluid, and in people who eat a high protein diet. Many people with this type of kidney stone also develop gout — a painful form of arthritis caused by solid deposits of uric acid in the joints.
- Struvite stones: These kidney stones are composed of magnesium, ammonia, and phosphate. They tend to occur in people who have repeated urinary tract infections
- Cystine stones: These kidney stones are relatively rare and associated with a disorder that a person may inherit from their parents in how their body processes cystine, which is a substance produced when the body digests protein. Cystine stones may first appear when a person is in their teens, 20s or 30s.
General factors that can increase the risk of developing kidney stones include:
- Family history of kidney stones
- Poor fluid intake or dehydration
- Diets high in salt, protein, sugar and vitamin D
- Structural problems that cause pooling of urine and infection in the kidney
- Having had previous kidney stones
- Excess body weight
- Some dietary supplements
- Some medications taken for other conditions, such as diuretics and corticosteroids.
Signs and symptoms
The pain is referred to as renal colic and may last for a brief time or for several hours before subsiding. Renal colic is caused by the ureter trying to expel the stone towards the bladder using a wave-like motion (peristalsis). Other symptoms that may be experienced include:
- Nausea and vomiting
- Blood in the urine — as the result of damage to the lining of the ureter or the presence of infection
- Fever or chills
- Urge to urinate, urinating more often than usual, and/or urinating in small amounts
- Repeated urinary infections.
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 that a CT scan or a special x-ray using contrast dye (an intravenous urogram) be performed to accurately identify the size and location of the kidney stones.
Initial treatment aims to relieve pain. This may include giving non-steroidal anti-inflammatory (NSAID) medications (eg: ibuprofen) and/or strong narcotic-based pain relief (eg: morphine). If pain and other symptoms are severe, admission to hospital may be necessary so that pain relief and fluids can be given via a drip into a vein (intravenously).
If infection is suspected or shown to be present, antibiotic medications may be given.
Underlying medical conditions that have led to the development of the kidney stones will need to be identified and treated in order to prevent recurrence of the kidney stones.
In the majority of cases the kidney stones will pass by themselves. In these cases, the only treatment required is adequate pain relief and plenty of fluids and rest. Medications may be given to relax the muscles in the ureter, helping the kidney stone to pass more quickly and with less pain. In the case of uric acid stones, medications may be given to help dissolve the stones.
In cases where the stones are too large to pass, the pain is excessive, or there is evidence of kidney damage or infection, further treatment to remove the stones may be necessary.
Kidney stones are generally removed in two main ways — surgery or lithotripsy. The method used to remove the kidney stones will depend on a variety of factors such as age, medical history and condition of the person, and size, type, and location of the stones.
The different surgical techniques used to remove kidney stones include:
- Ureteric stone removal (ureteroscopy) — where a long, thin tube with an eyepiece at its tip (ureteroscope) is passed via the urethra and bladder into the ureter to locate the stone. A tiny wire basket, which is passed into the ureter via the bladder, is used to grab and pull the stone free.
- Percutaneous nephrolithotomy (PCNL) — where a thin tube with a small video camera at its tip (a nephroscope) is inserted directly into the kidney through a small cut (incision) in the skin. The stone is located and removed via the tube or shattered by ultrasonic waves
- Open surgery — this may be necessary if the stones are large, are lodged in the kidney, and other techniques to remove the stones are unsuitable.
It uses high-energy shock waves to shatter the stones. Once the stones are disintegrated, the sand-like fragments that remain pass out of the body in the urine. Large stones may require more than one lithotripsy treatment.
For more about this treatment link to our Lithotripsy for Kidney Stones page.
Once a person has had a kidney stone, there is an increased likelihood they will have more. Steps that can be taken to prevent the development or recurrence of kidney stones include:
- Drinking plenty of fluid ¬ 2 litres per day is generally recommended
- Adequately treating underlying medical conditions
- Avoiding food with a high oxalate or salt content
- Eating meat in moderation.
In some cases, medications may be used to help prevent kidney stones reforming by controlling the amount of minerals and acid in the urine. The type of medication prescribed will depend on the kind of kidney stone the person has previously experienced, eg: thiazide diuretics for calcium stones and allopurinol for uric acid stones.
A referral to a dietitian may be recommended to manage dietary changes.
Further information and support
Healthpoint (2020). Kidney Stones (Patient Information). Auckland: Auckland Regional Urology Service (ADHB). https://www.healthpoint.co.nz/public/urology/auckland-regional-urology-service/kidney-stones/ [Accessed: 11/06/20]
Mayo Clinic (2020). Kidney stones (Web Page). Rochester, NY: Mayo Foundation for Medical Research. http://www.mayoclinic.org/diseases-conditions/kidney-stones/home/ovc-20319559 [Accessed: 11/06/20]
NHS Choices (2019). Kidney stones (Web Page). Redditch: National Health Service (NHS) England. http://www.nhs.uk/Conditions/Kidney-stones/Pages/Introduction.aspx [Accessed: 11/06/20]