A kidney stone is a structure formed when there is an increased concentration of substances, such as calcium, oxalate or uric acid in the urine. These substances initially form crystals initially and gradually increase in size, forming kidney stones. Stone may migrate or move down the urinary tract to be expelled in the urine. It can also become lodged in the urinary tract causing an obstruction to urine flow and usually severe pain. Most kidney stones are formed of calcium-containing material, primarily calcium oxalate. Stones can also be made of other substances, such as uric acid.
Certain diseases and habits can affect a person’s risk for developing kidney stones.
1. History of kidney stones
Patients who have had a calcium stone in the past have the highest risk of future stone formation. After the first episode of stone, 40 % untreated patients have another stone within 5 years and an additional 40 % within the next 25 years.
2. Family history of stones
Persons with a positive family history of kidney stones are at increased risk for developing stones.
3. Structural abnormalities of the kidney or urinary tract
Anatomical abnormalities of kidney or the urinary tract can predispose to stone formation. A disease called polycystic kidney disease is one such condition associated with increased risk of stone formation.
Increased intake of protein and salt increase the risk of stone formation. Interestingly, higher levels of dietary calcium intake appear to protect against rather than cause stone formation. This is probably due to the fact that dietary calcium combines with dietary oxalate, decreasing the absorption of oxalate from the intestine and subsequent excretion in the urine. These changes are reversed and stone formation may be enhanced with a low calcium diet. However, certain individuals who absorb excess calcium from their diet may experience additional stone problems with a high calcium intake. The best recommendation regarding dietary calcium is to avoid excessive intake of calcium, as well as low calcium diets. Drinking large amounts of water or other liquids has been linked to a reduced risk of stone formation. On the other hand drinking large quantities (more than one liter per week) of soft drinks acidified with phosphoric acid (Colas) seems to cause a modest increase in the risk of stone disease.
5.Other medical conditions
Some medical conditions can increase an individual’s risk for stone formation, including conditions that increase the absorption of oxalate from the gastrointestinal tract (like short bowel syndrome, chronic diarrhea, or previous bowel surgery). Urinary tract infections also increase the risk of stone formation. Patients who have a high concentration of uric acid in their urine are also at an increased risk stone formation. Cystinuria (increased levels of cystine in the urine) is caused by an inherited condition and increases the risk of cystine stone formation.
Symptoms are usually produced as a stone passes from the kidney into the ureter (the tube that leads from the kidney to the bladder).
Pain is the most common symptom. It can be mild or severe requiring hospitalization. Typically, the pain increases and decreases in severity. Severe pain is related to movement of the stone in the ureter and the resulting ureteric spasm. An episode of severe pain usually lasts 20 to 60 minutes.
Pain occurs on the side of the stone. The location of the pain depends upon the location of the stone and may change as the stone migrates. A stone causing obstruction in the upper ureter or renal pelvis leads to flank pain (pain in the side, between the ribs and the hip). A stone obstructing the lower portion of the ureter causes pain in the lower abdomen. Pain may also be felt over the region of genitalia (sexual organ) that may radiate to the genitals.
Hematuria, or blood in the urine, occurs in most patients with kidney stones. It may be visible to the naked eye or may be visible only by microscopic examination.
Patients may pass “gravel” or small stones. Uric acid stones, in particular, are more likely to present with gravel, but can also produce acute obstruction.
Other symptoms commonly seen include nausea, vomiting, pain with urination, and an urgent feeling of needing to urinate (also called “urgency”). In some patients, the stone gets stuck in the ureter, leading to blockage of urine flow.
Asymptomatic kidney stones
Many patients with kidney stones have no symptoms. (“Asymptomatic” means the absence of symptoms.) These stones are detected when x-ray studies are performed in those individuals with a prior history of stones, or when a radiologic study of the abdomen is performed for other purposes. Asymptomatic patients can remain symptom-free for years.
Clinical symptoms, laboratory tests, and diagnostic x-ray studies may all be used to diagnose a kidney stone. Hematuria (blood in the urine), flank pain, and a history of acute onset are particularly suggestive of a kidney stone. Analysis of a urine sample should be performed to look for the presence of blood or crystals. In addition, a radiologic test is typically performed to confirm the presence of a stone and to rule out other conditions, especially if the patient has no previous history of stones. A number of radiologic tests have been used, but computed tomography (CT scan) is now the preferred diagnostic test in most patients.
Many types of kidney stones can be seen on standard abdominal x-ray. However, certain stones, such as uric acid stones and small stones, may not be seen. As a result, other tests including a CT scan may be required if the history is suggestive and the plain x-ray is negative.
Ultrasonography (the use of sound waves to visualize body structures) can detect most stones, although small stones might be missed. It is the procedure of choice for patients who should avoid radiation, including pregnant women and possibly women of child bearing age.
Intravenous pyelogram (IVP)
In an IVP, a radiopaque dye (one that is detectable by x-ray) is injected into the bloodstream. The dye collects in, and is excreted by, the kidneys. As the dye passes through the kidney and into the bladder, the urinary tract and any kidney stones are visible on x-ray.
Computed tomography (CT) scan
A CT scan is a radiologic test that creates a three dimensional image of bodily structures. A particular type of CT scan (called noncontrast spiral CT) without contrast can visualize almost all kidney stones, including those that may not be seen by other tests, as well as the presence of urinary tract obstruction. This test has become the gold standard (the ideal test) for the initial radiologic diagnosis of stone disease. All stone compositions, including uric acid stones, can be visualized with a CT scan.
During the acute phase, many patients require only painkillers and fluids until the stone is passed. Painkillers may be prescribed for pain and can be given intravenously or orally. Fluids are given to increase urine flow and facilitate passage of the stone.
Stones smaller than 5 mm, and even those up to 7 mm, often pass spontaneously. Larger stones, however, usually do not come out and require some type of intervention. Several procedures are available for the treatment of these kidney stones.
Extracorporeal Shockwave lithotripsy (SWL)
In SWL, high-energy shock wave is directed toward the stone, passing through the skin and bodily tissues and causing a release of energy at the stone surface. This energy causes the stone to break into fragments that can be more easily passed. This is the treatment of choice in many patients who need help passing a stone, and is particularly good for stones in the renal pelvis and upper ureter. Stones that are large, hard, or complex cannot be treated by ESWL, x-rays or ultrasound are used to pinpoint the location of the stone. A.
Percutaneous Nephrolithotomy (PNL)
Extremely large or complex stones, or stones resistant to ESWL may be removed by this method. In this approach, small telescopic instruments are passed through the skin and into the urinary tract to access the stone directly.
CAN KIDNEY STONES BE PREVENTED? – A number of steps can be taken to decrease the chance that another stone will develop.
Prevention after the first stone
After a patient has had a kidney stone, blood and urine tests are often performed to identify factors that may contribute to stone formation. In addition, if the stone has passed and been saved, its composition should be analyzed.
1.Patients who have history of stone disease should increase their fluid intake to three liters per day, including drinking at night. The increased fluid intake will increase the urine flow rate and lower the concentrations of substances within the urine that promote stone formation.
2.To reduce the intake of protein of animal origin (Meat, Fish, Cheese etc.) to less than 1.5 gm/ Kg of body weight per day.
3.Salt intake intake to be restricted to 2 grams daily.
4.Among patients with calcium stones, limiting calcium intake is not recommended. As mentioned above, a low calcium diet may increase the risk of calcium stones in some individuals.
5.Reduce the intake of oxalate containing food. Green leafy vegetable nuts and tea are rich in oxalate.
An abdominal x-ray or ultrasound may be performed one year after the first stone to screen for new stone formation. If no new stones are found, screening may be repeated every three to five years thereafter.
Prevention in patients with recurrent stones
A more extensive work-up is generally recommended for a patient who has had previous stones or who is at higher risk for developing recurrent stones. Special tests are performed to analyze the patient’s urine and blood and determine whether underlying conditions may be contributing to stone formation. Examples include too much calcium or uric acid in the urine, which can be treated with specific medications to reduce the incidence of new stone formation.
Dr Abi Abraham M recognized nationally as well as internationally as an expert in the field of nephrology and kidney transplantation. He has more than 23 years of experience both as a clinician and academician. He has a wide range of experience in renal transplantation, critical care nephrology, vasculitis, lupus and electrolyte disorders. He has been awarded three prestigious fellowships, has widely cited publications in peer-reviewed journals, memberships in many renal societies and held administrative positions in organizations..