Uric acid crystals make up about 10-15% of all kidney stones. They form when your urine is too acidic, which happens more often in people with diabetes or metabolic syndrome (1, 2, 3).
The good news is that uric acid crystals are the only type that can dissolve with medication. In this article, we’ll explore what causes these crystals, their symptoms, how doctors treat them, and what you can do to prevent them.
Table of Contents
What Are Uric Acid Stones?
Uric acid stones are one of four main types of kidney stones. They form when uric acid crystals build up in your kidneys or urinary tract.
These crystals develop when your urine is too acidic. Normal urine has a pH between 5.9 and 6.8, but uric acid crystals form when pH stays below 5.5 (4, 2).
How They’re Different from Other Stones
Unlike calcium stones, uric acid crystals can’t be seen on regular X-rays. Doctors call them “radiolucent” stones because X-rays pass right through them.
The biggest advantage is that uric acid crystals in urine are the only kidney stones that can dissolve with medication. Other stone types usually need procedures to break them up or remove them.
Who Gets Them
Certain people have higher risk for uric acid crystals. This includes people with diabetes, obesity, gout, or metabolic syndrome.
Men develop uric acid crystals more often than women. Family history also plays a role, as some people inherit a tendency to produce acidic urine.
What Are the Symptoms?
Uric acid crystals cause similar symptoms to other kidney stones. The main problem is pain from the crystals blocking or irritating your urinary system.
Pain Locations
You might feel pain in your lower back, sides, abdomen, or groin area. The pain can be severe and may come in waves.
Small crystals might pass with minimal discomfort. Larger stones cause more intense pain as they move through your system.
Other Common Symptoms
Besides pain, you may notice blood in your urine. Your urine might also look cloudy or smell bad.
Some people experience nausea, vomiting, fever, or chills. These symptoms need immediate medical attention.
What Causes Uric Acid Crystals in Urine
Uric acid crystals form when your urine stays too acidic. Several factors contribute to this problem.
Low Urine pH
The main cause of uric acid crystals is persistently acidic urine. Your urine pH needs to stay below 5.5 for these crystals to form (5).
People who form uric acid crystals have different patterns of acid in their urine. Their pH stays lower all day long compared to people without stones.
Metabolic Conditions
Type 2 diabetes significantly increases your risk for uric acid crystals. People with diabetes have lower urine pH even when other factors are controlled (6, 7).
Metabolic syndrome as a whole increases stone formation risk by about 22%. People with three or more metabolic syndrome traits have much higher rates of kidney stones (8, 9).
Obesity also increases crystal risk. The risk is 35% higher in obese individuals, with stronger effects in North America than Asia (10, 11).
Dietary Factors
What you eat affects your crystal risk. Animal protein from beef, chicken, and fish all increase uric acid in your blood and urine (12).
Foods particularly high in purines include organ meats like liver and kidneys, shellfish, sardines, and anchovies. Red meat and meat-based gravies also contain high levels.
Fructose from table sugar and high fructose corn syrup also raises your crystal risk. It increases uric acid levels and makes urine more acidic (13).
How Do Doctors Diagnose Uric Acid Stones?
Doctors use several tests to identify uric acid crystals. Each test provides different information about your stones.
Imaging Tests
CT scans are the best way to see kidney stones. Uric acid crystals appear less dense than calcium stones on these scans.
Regular X-rays often can’t see uric acid crystals. Ultrasound can detect them but may miss smaller stones.
Urine Tests
A 24-hour urine collection tells doctors a lot about your crystal risk. They check your urine pH, uric acid levels, and other important markers.
Most people with uric acid crystals have a urine pH below 5.5. The test also shows if you’re making too much uric acid.
Treatment Options
Uric acid stones respond well to treatment. Many people can avoid surgery with the right medical therapy.
Dissolution Therapy
Medications can dissolve existing uric acid crystals. A systematic review of over 1,000 patients found that 80.5% achieved complete or partial stone dissolution (1).
About 61.7% of patients achieve complete crystal dissolution. Another 19.8% get partial dissolution, and only 15.7% need surgery.
Alkali Therapy
Potassium citrate is the most common treatment. It makes your urine less acidic, which helps dissolve crystals and prevent new ones.
Calcium carbonate tablets also work to raise urine pH. Both medications are safe for long-term use when monitored by your doctor.
Studies show citrate works as well as sodium bicarbonate for raising urine pH. However, citrate causes fewer side effects and gout flares (14).
Some research suggests adding theobromine (found in chocolate) to citrate might work even better. One study found the combination slightly reduced crystal risk more than citrate alone (2).
Uric Acid-Lowering Medications
Allopurinol reduces how much uric acid your body makes. It’s especially helpful for people with gout or very high uric acid levels.
Newer medications like febuxostat and benzbromarone also lower uric acid effectively. Both drugs work well even in people with kidney disease (15).
These medications can even shrink existing crystals. Some patients in studies had their stones completely disappear with treatment.
Medications for Metabolic Syndrome
For people with diabetes or metabolic syndrome, certain diabetes medications can help. Pioglitazone increases urine pH from 5.37 to 5.59 after 24 weeks of treatment (16).
SGLT2 inhibitors like canagliflozin and empagliflozin also help. They reduce uric acid levels and crystal formation risk in people with diabetes. Canagliflozin helps in people with diabetes (17), while empagliflozin has shown benefits even in non-diabetic patients (18).
Medications to Help Stones Pass
Alpha-blockers like tamsulosin can help ureteral crystals pass faster. These medications relax the muscles in your ureter.
Studies show tamsulosin increases stone passage rates to 88.9% compared to 51.1% without treatment. It also shortens passage time and reduces pain episodes (19).
Alpha-blockers work better for larger stones. They increase passage rates by 45% for stones over 5mm but show little benefit for stones under 5mm (20).
When Is Surgery Needed?
Most people avoid surgery with medical treatment. However, about 16% of patients still need surgical intervention.
Surgery becomes necessary when stones are very large (over 2cm), block urine flow, or cause infection. Stones that don’t pass after 4-6 weeks of medical treatment may also need removal (3).
Surgical Options
Extracorporeal shock wave lithotripsy (ESWL) uses sound waves to break crystals into smaller pieces. It works best for stones under 2cm and doesn’t require any incisions.
Ureteroscopy involves inserting a thin scope through your urethra to remove or break up crystals. Doctors use this for larger stones or when ESWL doesn’t work.
Percutaneous nephrolithotomy (PCNL) is reserved for very large stones. The surgeon makes a small incision in your back to access and remove the stone directly.
Small crystals under 7 millimeters often pass on their own within 3 weeks. Drinking plenty of water and taking alpha-blockers helps them pass more easily.
When to Seek Emergency Care
Most kidney stones can be managed at home with medications. However, some situations require immediate medical attention.
Warning Signs of Infection
Sepsis is a rare but serious complication of kidney stones. Women and people with high white blood cells in their urine have higher risk (21).
Seek emergency care if you have severe pain with fever over 101.5°F. This combination often signals a serious infection needing urgent treatment.
Other Emergency Symptoms
Go to the emergency room if you experience persistent vomiting that prevents drinking fluids. Dehydration makes crystals worse and harder to pass.
Visible blood in your urine with severe pain also needs immediate evaluation. These symptoms together may indicate the stone is causing damage.
What Lifestyle Changes Help?
Diet and lifestyle changes play a big role in preventing uric acid crystals. Small changes can make a big difference.
Dietary Modifications
Limit animal protein to reduce your crystal risk. Keep portions to 4-6 ounces per day.
Foods to limit or avoid include:
- Organ meats: Liver, kidneys, and sweetbreads
- Certain seafood: Sardines, anchovies, and shellfish
- Red meat: Beef and pork
- Meat gravies: High in concentrated purines
Cut back on fructose from sugary drinks and sweets. High fructose intake makes your urine more acidic and increases crystal risk.
Weight loss also helps if you’re overweight. One study found that diet with meal replacement improved uric acid levels more than diet alone (22).
Hydration
Drink plenty of water throughout the day. Aim for enough fluid to produce 2.5 liters of urine daily.
This usually means drinking about 3 liters of fluid per day. You need more in hot weather or during exercise (23).
Space your water intake evenly. Don’t try to drink it all at once.
Can uric acid crystals dissolve on their own?
How long does it take to pass a uric acid stone?
Are uric acid crystals visible on X-ray?
What foods should I avoid with uric acid stones?
What urine pH prevents uric acid crystals?
The Bottom Line
Uric acid crystals are highly treatable kidney stones that respond well to medical therapy. About 80% of people can avoid surgery with proper treatment, though these crystals have high recurrence rates without prevention.
The key is raising your urine pH with alkali therapy and managing any underlying conditions like diabetes or gout. Diet changes, weight loss, and good hydration also make a big difference.
Alpha-blockers can help stones pass faster if they’re in your ureter. With the right treatment plan, most people can dissolve existing crystals and prevent new ones from forming. Talk with your doctor about which approach works best for your situation.