Uric Acid Stones
What are uric acid stones?
A uric acid stone is a type of kidney stone, which is a hard object that is made from chemicals in the urine. After formation, the stone may stay in the kidney or travel down the urinary tract into the ureter. Stones that don't move may cause significant pain, urinary outflow obstruction, infection, or other health problems.
What are the symptoms of uric acid stones?
A stone that is small enough can pass through with no symptoms. However, a stone that is too large to pass through may cause significant pain, back-up of urine, infection and other health problems. Speak with a healthcare professional if you feel any of these symptoms:
- Severe pain on either side of your lower back
- Vague flank pain or stomach ache that doesn’t go away
- Blood in the urine
- Nausea or vomiting
- Fever and chills
- Urine that smells bad or looks cloudy
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What causes uric acid stones?
Foods such as beef, poultry, pork, fish, and particularly organ meats such as liver, have high amounts of a natural chemical compound known as purines. Uric acid can result from a diet high in purines. High purine intake leads to a higher production of monosodium urate, which, under the right conditions, may form uric acid stones in the kidneys. Uric acid stones form when the levels of uric acid in the urine are too high, and/or the urine is too acidic on a regular basis.
The formation of these types of stones can run in families. Inherited problems in how the body processes uric acid or protein in the diet can increase the acid in urine. This can be seen in conditions such as gout, a condition where people can have high levels of uric acid in the blood and painful deposits of crystals in the joints. There is also an increased risk of uric acid stones in people with diabetes. Patients receiving chemotherapy are also at risk of having uric acid stones.
How can uric acid stones be prevented?
Drinking enough water each day is important in maintaining overall health and will help keep your urine less concentrated with waste products. Darker urine is more concentrated, so your urine should appear light yellow to clear if you are well hydrated. Drinking enough fluids to make at least two liters of urine per day may be recommended. Fluid restrictions might apply if you have advanced kidney disease, so speak with a healthcare professional about the right amount of water for you.
Maintaining a healthy weight is also important for managing overall health and in preventing kidney stones. Being overweight increases your risk of kidney stones. Managing blood pressure and controlling salt intake is also important. A dietitian can help you plan meals to help you lose weight.
To help prevent uric acid stones, cut down on high-purine foods such as red meat, organ meats, beer/alcoholic beverages, meat-based gravies, sardines, anchovies and shellfish. Follow a healthy diet plan that has mostly vegetables and fruits, whole grains, and low-fat dairy products. Limit sugar-sweetened foods and drinks, especially those that have high fructose corn syrup. Limit alcohol because it can increase uric acid levels in the blood and avoid short term diets for the same reason. Decreasing animal-based protein and eating more fruits and vegetables will help decrease urine acidity and this may help reduce the chance for uric acid stone formation.
Citrate might be prescribed to help prevent certain stones, such as uric acid stones, if urine citrate is low and urine pH levels are too low (or too acidic). Citrus juices do contain citrate (citric acid), but large amounts might be needed. Also, be careful of sugar. Lemon juice concentrate (4 oz per day) mixed with water can be considered. Alkali citrate can be prescribed (such as potassium citrate) and is available over-the-counter. Alkali citrate can be given with a mineral(s), such as sodium, potassium or magnesium to help prevent stone formation. The aim is to increase urine citrate (for prevention of calcium stones) and increase urine pH (or make urine less acidic or more alkaline, for prevention of uric acid and cystine stones). The goal is to keep pH in balance. Speak with a doctor or other healthcare professional about which treatment options are right for you, including over-the-counter products and home remedies. This may not apply to all types of stones, so speaking with a healthcare professional is important. People with kidney disease may need to watch their intake of sodium, potassium or other minerals, depending on the stage of kidney disease or other factors.
How is a uric stone diagnosed?
Diagnosis of a kidney stone starts with a medical history, physical examination, imaging tests, urine and blood testing, and stone analysis. Blood and urine can be tested for abnormal levels of certain chemicals. You may be asked to collect your urine for 24 hours to test for uric acid or other factors that may increase the risk for stone formation.
Imaging tests can be used to locate stones in the body. Ultrasound uses a device to bounce safe, painless sound waves off organs and create an image of their structure. Many healthcare professionals feel that this is the best screening test to find stones. Computerized tomography (CT) scans uses a beam of X-rays and computers to create images and look for stones inside the kidneys.
A stone that comes out of the body will be analyzed in order to find the type of stone and its cause. Knowing the type of stone can also help with a plan for prevention.
What is the treatment for uric acid stones?
At first, drinking more water may be recommended. Medications can also be used either for pain or to help the stone pass.
Medications can include can include allopurinol to reduce uric acid levels in the blood. Other medicines can include citrate to make urine less acidic (or more alkaline). Other medications can include thiazide diuretics (water pills) or tamsulosin (to relax the ureter and help the stone pass).
If these treatments do not work, or if the stone is too large to pass through, then surgical procedures may be needed to break down larger stones or remove them. A ureteroscopy uses a small scope to remove the stone. Shock wave lithotripsy (SWL) uses high-energy acoustic pulses to break up the stone into smaller pieces for passing. Percutaneous nephrolithotomy (PCNL) removes the stone surgically through the back.