Kidney Stones

Kidney Stones - What it is

urinary stones conditions and treatments

The kidneys are two bean-shaped organs located below your chest, one on each side of the spine. Their function is to filter waste chemical compounds from the body into the urine. They remove extra water and wastes from the blood, producing urine. Additionally, the kidneys produce hormones and maintain a stable balance of salts in the blood.

Under certain conditions, the chemicals in the urine may form crystals, which combine to form urinary stones. These stones may block the flow of urine and cause severe pain, infection, and affect the function of the kidney. Urinary stones are usually found either in the kidney, the ureters (tubes that direct urine from the kidneys to the bladder), or in the bladder and the urethra.

A kidney stone is composed of crystals formed by chemicals that separate from the urine and build up in the kidney. The most common type of stone contains calcium oxalate or calcium phosphate. A less common type of stone, caused by infection in the urinary tract, is called a struvite stone. Other rarer stones include uric acid stones and cystine stones.

Narrow tubes called ureters carry urine from the kidneys to the bladder, an oval-shaped reservoir for urine in the abdomen.

What is a Kidney Stone?

Kidney stones or urinary stones (also known as urolithiasis or renal calculi) are solid deposits that occur within the urinary system. They occur when urine becomes too concentrated with minerals, which then precipitates into multiple small mineral crystals that can eventually accumulate to form stones. These stones can lead to complications especially if they cause obstruction within the urinary tract. This might then lead to severe back pain, blood in the urine, or even severe urinary tract infections.

Types of Kidney Stones

There are several types of kidney stones, but the four most predominant include:

Calcium stones

The most common, accounting for >80% of all stones.
Most are in the form of calcium oxalate. Oxalate is found naturally in many foods, and foods with high oxalate content include peanuts, beans, leafy vegetables and chocolate.
Another major group are calcium phosphate stones, which are usually associated with metabolic diseases, including hyperparathyroidism and renal tubular acidosis.

Uric acid stones

Accounts for ~10% of stones. These form when there are high concentrations of uric acid within the urine, which is commonly associated with gout, and can also occur when the urine is too acidic, or with a diet high in purines (red meat, organs, and seafood).

Struvite stones

These stones usually occur as a result of urinary tract infections with bacteria that break up urea, resulting in an alkaline urine that leads to precipitation of magnesium, ammonium and phosphate, the stone’s constituent salts.

Cysteine stones

Less common, and occurs in patients with cystinuria, a genetic condition that causes the kidney to excrete excessive amounts of certain amino acids that eventually crystallise into stones.

Kidney Stones - Symptoms

Kidney stones usually cause symptoms when they pass into one of the ureters. This causes obstruction to the flow of urine and swelling of the kidney, as well as spasms of the ureter. The following symptoms can occur:

Loin pain: A sudden and severe pain of the back and sides below the ribs, which can radiate downwards towards the groin (also known as renal colic).
Haematuria: Blood in the urine
Frequency and urgency in urination
Nausea and vomiting
Fever and chills: If there is superimposed infection

Many people may not feel any symptoms. The first symptom of a kidney stone is severe pain, which begins suddenly when a stone moves in the urinary tract and blocks the flow of urine. Typically, you will feel a sharp, cramping pain in your back and side, and around the area of the kidney. The pain may shift to the lower abdomen later on. Sometimes, you may also experience nausea and vomiting. As the stone moves and the body tries to push it out, blood may appear in your urine making the urine pink. As the stone moves down the ureter closer to the bladder, you may feel the need to urinate more often or a burning sensation during urination. If fever and chills accompany any of these symptoms, an infection may be present.

Kidney Stones - How to prevent?

You may reduce your risk of developing kidney stones if you:

Drink water. You should drink enough water to produce light and clear urine.
Reduce intake of oxalate-rich foods. These include spinach, sweet potatoes, nuts, tea, chocolate, and soy products.
Reduce salt and protein in your diet.
Continue eating calcium-rich foods, but use caution with calcium supplements. You may reduce the risk of stone formation by taking supplements with meals. Diets low in calcium can also increase kidney stone formation in some people. If in doubt, please consult your doctor or a dietician.

You are likely to form another if you have had more than one kidney stone. Therefore, prevention is important. Adequate water intake is crucial. If you tend to form kidney stones, try to drink enough liquid throughout the day to produce at least two litres of clear urine. Calcium intake is also important. Recent studies have shown that foods high in calcium, including dairy products, may help prevent calcium stones. Older women taking calcium supplements to prevent bone loss should continue to do so. Oxalate intake should be monitored, especially for those prone to forming calcium oxalate stones. Vitamin D intake and meat intake may also need to be regulated based on the type of stones formed.

Kidney Stones - Causes and Risk Factors

Why do Kidney Stones Occur?

Kidney stones occur when certain salts and minerals are present in excessive concentrations in the urine, and these eventually precipitate into small crystals that accumulate into stones. There is no single definite cause for the formation of stones, but is more likely due to several contributing factors that increase the risk of stone formation.

Risk factors include:

Age: Usually more common in older individuals ~40 – 60 years of age.
Obesity: Has been associated with >50% higher risk of stone formation.
Genetic: A history of kidney stones within the family is associated with a higher risk.
Dehydration: A lack of fluid intake leads to concentration of salts in the urine, increasing risk of stone formation.
Diet: Certain diets high in oxalate (nuts, long beans, chocolate), high in purines (red meat, organs, seafood).
Previous kidney stones: An individual with a diagnosed kidney stone has a 50% risk of developing another stone within the next 10 years.
Certain medical conditions: Diabetes, metabolic syndrome, hyperparathyroidism, renal tubular acidosis, gastrointestinal diseases (including inflammatory bowel disease, malabsorption, bariatric surgery, previous intestinal resections). Known conditions associated with urinary tract obstruction can also increase the risk of stone formation.
Use of certain medications: HIV medications (indinavir).

Kidney Stones - Diagnosis

Several tests will be performed when you seek a urologic specialist.

Imaging:

The gold standard investigation is a computerised tomography (CT) scan, which is highly sensitive and able to detect even small stones.

X-Rays of Kidneys and Bladder: These are commonly performed as a quick screening test especially in the emergency department but might miss small kidney stones.
Ultrasound: A simple non-invasive test that can also be performed quickly to evaluate for kidney stones or obstruction in the urinary system.
Intravenous urogram (IVU) or computerised tomography (CT) scan: These imaging techniques used to detect kidney stones by visualizing the urinary tract and identifying the presence and location of stones within the kidneys and urinary system.

Additional urine and blood tests may be needed to exclude infection and impairment of kidney function.

You may be asked to collect urine for 24 hours to measure urine volume and the levels of chemicals in the urine. Your doctor will also ask about your medical history, occupation, and eating habits.

Urine tests:

Urinalysis: Red blood cells in the urine might be caused by presence of a stone. Urinary nitrites might also suggest presence of infection. The pH of urine might suggest the underlying stone that is present (acidic urine for uric acid stones, alkaline urine for struvite stones).

Urine cultures: Urine is taken and cultured over a period of time to determine presence of bacteria in the urine.

Blood tests:

Metabolic workup: To evaluate if certain salts and minerals are raised within the blood, including calcium, phosphate and uric acid.

Creatinine: To evaluate renal function which can be compromised by presence of a kidney stone.

Kidney Stones - Treatments

Once diagnosed, the size and location of the stone are important in guiding the options for treatment.

Small Stones (Conservative)

Conservative treatment includes:

Drinking water: Drink as much 2-3 litres of water a day to keep your urine diluted and clear unless your doctor tells you otherwise.
Pain relief: You may be prescribed pain medications to minimise discomfort during stone passage.
Medical therapy: An alpha blocker, such as tamsulosin, may be prescribed to relax to muscles in your ureter, facilitating passage of stone with less pain.

Medical Therapy for Kidney Stones

Certain medications may help prevent calcium and uric acid stones by controlling the amount of acid or alkali in the urine which are key factors in crystal formation. The medicine allopurinol may also be useful in some cases of hyperuricosuria where the chemical uric acid is secreted in large amounts in the urine.

Surgical Treatment for Kidney Stones

There are three ways to treat kidney stones using surgery. This includes :

ESWL as a treatment for kidney stones

Extracorporeal shock wave lithotripsy (ESWL): ESWL uses sound waves delivered by an external device that resembles an X-ray machine that break stones into smaller pieces that can be passed out in your urine. ESWL may cause blood in urine, pain or bruising of your back or abdomen, bleeding around the kidney. Sometimes you may require more than one session to completely fragment the stones. Very rarely, the small fragments may be stuck in the ureter and cause obstruction of urine flow, which will require surgical management.

Complications may occur with ESWL. Bruising and minor discomfort in the back or abdomen from the shock waves can occur. To reduce the risk of complications, patients are normally told to avoid aspirin and other medicines that affect blood clotting for several weeks before treatment. Sometimes, the shattered stone particles cause a minor blockage of the urinary tract which requires the placement of a stent into the ureter to help the fragments pass. If the kidney stone is not completely shattered with one treatment, additional treatments may be needed.

Percutaneous nephrolithotomy (PCNL): This procedure involves a small incision over your back and inserting a telescope and instruments into the kidney to break the stones into smaller pieces. This procedure requires general anaesthesia. Potential complications of PCNL include bleeding, urinary tract infection, injury to adjacent organs and retained stones.

Ureteroscopic stone removal: A small telescope can be passed through your urethra and bladder to your ureter. Tools can be used to break stones into pieces that will be removed with a small basket or pass out in your urine. You may require general anaesthesia during this procedure. Your doctor may then place a stent (small plastic tube) in the ureter to prevent swelling and obstruction of the ureter and to promote healing. You may require more than one procedure to completely remove larger stones. If your ureter is too tight to pass the ureteroscope or instruments through, your doctor may choose to insert a stent in your ureter to allow muscles in your ureter to relax and you will come back another day (~1-2 weeks) to complete the procedure.

percutaneous nephrostomy as a treatment for kidney stones ureteroscopic stone removal as a treatment for kidney stones