Kidney Stones
The kidneys are bean-shaped, fist-sized organs located under the ribs, in the middle of the back. The kidneys filter waste materials and excess fluid from the blood and also produce hormones that are important for blood formation, blood pressure, and bone formation.
The kidneys are part of the urinary system which includes; the bladder, ureters (tubes from the kidney to the bladder) and urethra (tube from the bladder to the outside of the body).
Kidney stones (also called renal calculi) occur when substances within the urine precipitate and form solid material. 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. There may be a single stone or many stones.
Kidney stones can cause severe pain. 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.
Approximately 5 to 10% of the population in New Zealand are affected by kidney stones. They are more common in men than in women and occur more commonly in older people than in younger people.
There are several different types of kidney stones, classified by the substances that form them. The different types include:
Calcium stones
Approximately 80% of all kidney stones are calcium stones. They are composed of calcium in combination with either phosphate or oxalate. These occur when there are excess levels of calcium circulating in the blood.
Uric acid stones
Approximately 10% of all kidney stones are uric acid stones. These occur when excess amounts of uric acid are present in the blood. Approximately 50% of 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
Approximately 5% of all kidney stones are struvite stones. They are composed of magnesium ammonium phosphate and tend to occur in people who have repeated urinary tract infections.
Cystine stones
Approximately 2% of all kidney stones are cystine stones. Cystine is a type of amino acid. People with cystine stones usually have an abnormality with the way their body processes amino acids in the diet.
What Causes Kidney Stones
The build up of the substances that form kidney stones may be as a result of a number of factors including urinary tract infections, dehydration, certain medical conditions and metabolic imbalances. However, in the majority of cases the cause is unknown.
Factors that can increase the risk of developing kidney stones include:
- Family history of kidney stones
- Poor fluid intake or dehydration
- Structural problems that cause pooling of urine and infection in the kidney
- Having had previous kidney stones.
Medical conditions and metabolic problems that can cause the development of kidney stones include:
- Hypercalciuria – where there are excess levels of calcium in the blood leading to the development of calcium stones. 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.
- Urinary tract infections - these can increase the pH level of the urine causing it to become more alkaline. This is a common cause of struvite stones.
- Hyperuricosuria - a problem with uric acid metabolism, leading to the development of uric acid stones.
- Cystinuria - a rare disorder leading to the excess production of cystine, leading to the development of cystine stones.
- Hyperoxaluria - where there are excess levels of oxalate in the blood.
- Excess vitamin D intake.
The most common symptom of kidney stones is intense pain in the loin – the area of the back between the bottom of the ribs and the hip bone. The pain can radiate down to the groin region. The pain is referred to as renal colic and can last for several hours before subsiding. Renal colic is caused by the ureter trying to expel the stone towards the bladder though 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
- Repeated urinary infections.
If kidney stones are suspected, it is important that a doctor is consulted promptly for diagnosis and treatment.
Often a diagnosis of kidney stones can be made based on the presenting symptoms and the presence of blood in the urine. An ultrasound scan and a plain abdominal X-ray are usually performed to confirm 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 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 for kidney stones aims at relieving pain. This may include strong narcotic based pain relief such as 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.
In cases where the stones are too large to pass, the pain is excessive, there is evidence of kidney damage or infection, further treatment to remove the stones may be necessary.
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.
Surgery
The different surgical techniques used to remove kidney stones include:
- Ureteric stone removal – Where a tube is passed via the urethra and bladder into the ureter, where the kidney stones are located and removed
- Percutaneous nephrolithotomy – Where a thin tube (nephrostomy tube) is inserted directly into the kidney through 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.
Lithotripsy (extracorporeal shock wave lithotripsy – ESWL)
Lithotripsy is a non-invasive alternative to surgery that 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.
Once there has been a kidney stone, there is an increased likelihood of recurrence. It is estimated that 30 – 50% of people will develop a further kidney stone within five years of developing the first kidney stone.
Steps that can be taken to prevent the development or recurrence of kidney stones include:
- Drinking plenty of fluid - up to 2 litres per day is recommended
- Adequately treating underlying medical conditions
- Avoiding food with a high oxalate or salt content
- Eating meat in moderation.
A referral to a dietitian may be recommended to manage dietary changes.
Further Information and Support
For further information contact your doctor or practice nurse or contact:
Kidney Health New Zealand
POBOX 139
Christchurch
E-mail: info@kidneys.co.nz
Website: www.kidneys.co.nz
Phone: (03) 353 1242
Fax: (03) 374 2176
Freephone: 0800 KIDNEY (0800 543 639)
Carson-De Witt, R. (2006) Kidney Stones. The Gale Encyclopaedia of Medicine. In, Health and Wellness Resource Centre. Thompson Gale. Farmington Mills, MI.
Davidson, A.M, Cumming, A.D., Swainson, C.P. &.Turner, N. (1999) Diseases of the kidney and urinary system. In C.R.W. Edwards, I.A.D. Bouchier, C.Haslett & E.R. Chilvers (eds.) Davidson’s principles and practice of medicine (18th ed.) (pp 417-470). Edinburgh: Churchill Livingstone
New Zealand Kidney Foundation (2003) Kidney stones. Pamphlet. New Zealand Kidney Foundation. Christchurch
Last Reviewed – 7/02/07