This is a urine test to see whether you have a high level of the chemical oxalate in your urine. Oxalate is a natural end product of metabolism in the body and should be expelled through your urine. If your oxalate levels are too high, the excess oxalate can combine with calcium to form kidney stones. These stones are hard masses of chemicals that can get stuck in the urinary tract and commonly cause severe pain. Calcium-oxalate kidney stones are the most common type. Increased levels of oxalate may be a result of eating foods high in oxalate, or absorbing or making too much oxalate.
If you have frequent kidney stones, your doctor might order this test to help him or her make a recommendation on treatment. It may also be used to find out how well restricting your dietary oxalate is working. You might have this test to see whether you have a rare inherited condition known as primary hyperoxaluria and are at risk of developing kidney stones.
Your doctor might also order tests to look for other chemicals in your urine: glycolate and glycerate. He or she may also want a blood sample to test for a genetic form of hyperoxaluria.
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.
The normal level of urine oxalate excretion is less than 45 milligrams per day (mg/day). A higher level of urine oxalate may mean you are at risk of developing kidney stones. Risk of stone formation seems to increase even at levels above 25 mg/day, which is considered within normal limits.
This test requires a urine sample collected over 24 hours. Your doctor will tell you how to collect the sample.
Consuming foods high in vitamin C can affect your test results. In the body, vitamin C is changed into oxalate. Your test results also may be affected by an inflammation of the bowel or if you've had intestinal or colon surgery. Studies don't say for sure whether eating spinach, peanuts, chocolate, and other foods high in oxalate can increase oxalate in your urine.
Avoid eating or drinking any food with vitamin C for 24 hours before you collect your urine sample.