Kidney stones, also known as renal calculi, nephrolithiasis or urolithiasis, are solid masses made up of minerals and salts that can grow to the size of a golf ball and form inside the kidneys. Kidney stones are the result of a build-up of minerals that generally start in your kidneys; however, they can develop anywhere along the urinary tract such as the ureter, bladder or urethra.
Kidney stones can develop in one or both kidneys and are most common in people aged 30 – 60, affecting around 1 in 10 people. They can be extremely painful and can cause kidney infections or kidney failure if left untreated.
Kidney stones have many causes, depending on the type of stone, from diet and excess body weight to medical conditions and medications. Passing kidney stones can be quite painful; however, the stones generally cause no permanent damage if detected early.
Depending on your circumstances, you may require nothing more than painkillers and plenty of water to pass the stone. In some cases, they can lodge in the urinary tract, where surgery may be required. Your doctor may suggest preventive treatment to minimise your chance of recurrent kidney stones if you are at increased risk of developing them again.
Types of Kidney Stones
Not all kidney stones are formed of the same crystals. There are 4 main types of kidney stones including:
Calcium
Calcium stones are the most common type of kidney stone. They are typically formed when calcium combines with oxalate in the urine. Insufficient calcium and fluid intake, as well as other conditions can cause them to form. Eating less oxalate-rich foods such as peanuts, chocolate and spinach, can minimise your risk of developing this type of stone.
Uric acid
This is a common type of kidney stone more often found in men than in women. High purine foods such as shellfish, meat and fish can lead to a higher chance of developing this them. They can develop in people with gout or those undergoing chemotherapy. They tend to run in families.
Struvite
This type of stone is less common and is commonly found in women with urinary tract infections (UTIs) or a kidney infection. They can be large and cause urinary obstruction. Treating the primary infection can prevent the development of struvite stones.
Cystine
Cystine stones are rare and typically run in families that have the genetic disorder cystinuria. They are caused by a natural bodily acid leaking into the kidneys and urine.
Causes and Risk Factors
Kidney stones often have no primary, single cause. Kidney stones develop when urine contains more crystal-forming matter, such as calcium, uric acid and oxalate, than fluid in your urine can dilute.
There are a number of factors that can increase your risk of your forming kidney stones, including:
Dehydration
Not drinking enough water can increase your risk of developing kidney stones. People who live in warm, dry environments or sweat a lot may also be at higher risk.
Obesity
A large waist size, weight and high body mass index (BMI), have been connected to an increased risk of kidney stones.
Diet
A diet with high levels of protein, sodium (salt) and sugar can increase your risk of developing certain types of kidney stones, particularly with a high sodium diet. Excessive salt in your diet increases the level of calcium your kidneys need to filter and significantly increases the risk of kidney stones.
Personal or family history
If a member of your family has experienced kidney stones, or you have already had them before, it is more likely that you will develop them or experience them again.
Digestive diseases and surgery
Inflammatory bowel disease, gastric bypass surgery, or chronic diarrhoea can trigger changes in the digestive system that escalate your absorption of calcium and water, increasing the amount of stone-forming matter in your urine.
Certain supplements and medications
Dietary supplements, laxatives (when used excessively), vitamin C, calcium based antacids and some medications used to treat depression and migraines can increase your risk of kidney stones.
Symptoms
Kidney stones can cause severe pain; however, symptoms may not appear until the stone moves around the kidney or passes into the ureters. If it lodges in your ureters, it can block the flow of urine, causing the kidney to swell and ureter to spasm, resulting in extreme pain known as renal colic. The pain may be intermittent but can be intense. In men, the pain may radiate to the groin area.
In the majority of cases, kidney stones pass without causing damage. However, passing a kidney stone can result in severe pain. For small stones, pain relievers may be the only treatment necessary. Other stones that cause lasting symptoms, extreme pain or other complications may require further treatment such as surgery.
Kidney stones range in size; from a grain of sand to a golf ball. As a rule, the larger the kidney stone, the more obvious the symptoms. Symptoms you may experience include:
- Pain in the side of your abdomen or groin
- A high temperature or fever
- Nausea or vomiting
- Intermittent pain
- Blood in your urine (pink, red or brown urine)
- Foul-smelling, cloudy or discoloured urine
- A frequent need to urinate
If a kidney stone blocks the ureter, it can result in a kidney infection. This occurs due to waste products unable to pass the blockage, resulting in a build-up of bacteria. A kidney infection shows some of the same signs as kidney stones, but may also include:
- Feeling weak and fatigued
- Diarrhoea
- Chills and shivering
- Extreme pain on either side of the lower back
- Constant general pain or stomach ache
- A stinging or burning sensation while urinating
Pain due to a kidney stone may change location or intensity, for instance as the stone moves through your urinary tract.
Seek medical attention if you have any worrying symptoms.
Diagnosis
Your doctor will generally be able to diagnose kidney stones based on your medical history and symptoms, particularly if you have previously had kidney stones. Your doctor may order other tests such as:
- Urine tests to check for infection and fragments of stones
- An assessment of any stones that you pass in your urine
- Blood tests to confirm that your kidneys are functioning normally and to check the levels of substances that can cause kidney stones, such as calcium or uric acid
If you have pain that may be a result of kidney stones, your doctor should refer you to a hospital for a scan as soon as possible. Pregnant women and children younger than 16 should have an ultrasound.
If your doctor expects an obstruction, they may order the following tests:
- Abdominal X-rays
- Intravenous pyelogram (IVP)
- Retrograde pyelogram
- Ultrasound of the kidney (the preferred test)
- MRI scan of the abdomen and kidneys
The contrast dye used in the scan and the IVP can sometimes affect kidney function. However, in people with typical kidney function, this is not a concern.
Treatment
The majority of kidney stones are small enough to pass in your urine and can improve with the use of home treatments.
Home treatment steps include drinking plenty of fluids. It is important to drink enough fluid throughout the day; however, you should avoid fizzy drinks. Your urine should be pale in colour; if it is dark, this signifies you are not drinking enough.
Over the counter medication such as ibuprofen will help with any pain or discomfort whilst you are carrying out home treatments. Alpha-blockers might be recommended to help the stone pass.
If your kidney stones are too big to be passed naturally, they are usually removed by surgery. The leading methods of surgery for removing kidney stones include:
- Shockwave lithotripsy (SWL)
- Ureteroscopy
- Percutaneous nephrolithotomy (PCNL)
The type of surgery performed will depend on the size and location of your stones.
Extracorporeal shock wave lithotripsy (ESWL)
ESWL uses shock waves to locate the kidney stone and break it down into smaller pieces that can be passed through the urinary tract and through your urine. You may require more than one session of ESWL to treat your kidney stones.
Ureteroscopy
Ureteroscopy involves passing a ureteroscope (a long, thin telescope with a camera at the end) through the urethra (the tube urine passes through) and in to your bladder. It is then moved into your ureter (the connection between your bladder and kidney). Your doctor may use a small cage to remove the stone. They may also use a laser to break it into small pieces to naturally pass through your urine. The stone is then sent to the laboratory for analysis.
Percutaneous Nephrolithotomy (PCNL)
PCNL involves passing a nephroscope (a thin telescopic instrument) through a small incision in your back and in to your kidney. The stone is either pulled out or broken into smaller pieces.
Risks and Complications
Possible complications will depend on the method of treatment you have and the size and location of your stones.
Complications include:
- Sepsis, an infection that spreads through the blood, triggering symptoms throughout the whole body
- A blocked ureter caused by stone fragments
- Damage to the ureter
- A urinary tract infection (UTI)
- Pain
- Bleeding or blood clots
Outlook
Treatment is personalised depending on the type of stone and location. The outlook for kidney stones is generally very positive, although there is the risk of recurrence.
In many cases, kidney stones can gradually pass on their own without any treatment.
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