Urinary Stones (Kidney Stones)

Urinary Stones (Kidney Stones) - What it is

urinary stones conditions and treatments

The function of the kidneys is to filter waste chemical compounds from the body into the urine. Under certain conditions, the chemicals in the urine may form crystals, which combine to form urinary stones.

Urinary 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.

What is a Kidney Stone?

Kidney 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.

Urinary 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. It is also important to note that symptoms might not be related to

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

Urinary Stones (Kidney Stones) - How to prevent?

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

Drinking 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.

Urinary Stones (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

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).

When to see a doctor

It is pertinent to seek medical attention when complications of kidney stones arise, and these can include:

Severe pain, not responding to painkillers
High fever, with temperature >38°C. Infections that occur when urine is obstructed in the urinary system can be severe and life-threatening, and immediate medical attention is crucial.
Visible haematuria (blood in the urine)
Symptoms of renal failure: Severe shortness of breath, swelling of both legs

Urinary Stones (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: 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.

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.

Urinary Stones (Kidney Stones) - Treatments

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

Small stones - Conservative

Most small stones do not require surgical treatment. Conservative treatment include:

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.

Large stones – Surgical Management

Stones that are too large to pass on their own or cause bleeding, persistent severe pain that cannot be controlled, renal impairment and infection of the urinary tract may require invasive treatment. These are the option:

Extracorporeal shockwave therapy (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. You will be given painkillers to make you more comfortable.

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.
Ureteroscopy: 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 will 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 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. You may wake up with a tube behind your back to help drain the urine and stone fragments. This will be removed in 1-2 days before you are discharged home.

Potential complications of PCNL include bleeding, urinary tract infection, injury to adjacent organs and retained stones.

Urinary Stones (Kidney Stones) - Preparing for surgery

Urinary Stones (Kidney Stones) - Post-surgery care

Urinary Stones (Kidney Stones) - Other Information

Overview

Article contributed by Urology, Singapore General Hospital

The information provided is not intended as medical advice. Terms of use. Information provided by SingHealth

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