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  Back Blood-tests Explained


Uric Acid


At a Glance

Why Get Tested?

To detect high levels of uric acid in the blood, which could be a sign of the condition gout, or to monitor uric acid levels when undergoing chemotherapy or radiation treatment; to detect high levels of uric acid in the urine in order to diagnose the cause of kidney stones and to monitor those with gout who are at risk of developing such stones

When to Get Tested?

When you have joint pain or other symptoms that your doctor suspects may be due to gout; when you have had or are going to have certain chemotherapy or radiation therapies for cancer; when you have recurrent kidney stones; when you have gout or are otherwise at risk for kidney stone formation

Sample Required?

A blood sample drawn from a vein in the arm or a 24-hour urine sample

Test Preparation Needed?

None may be needed; however, some institutions recommend fasting. Follow any instructions you are given.

The Test Sample

What is being tested?

Uric acid is produced by the breakdown of purines. Purines are nitrogen-containing compounds found in the cells of the body, including our DNA. As cells get old and die, they break down, releasing purines into the blood. To a lesser extent, purines may come from the digestion of certain foods, such as liver, anchovies, mackerel, dried beans and peas and certain alcoholic drinks, primarily beer. Most uric acid is removed from the body by the kidneys and is excreted in the urine, with the remainder eliminated in the stool. This test measures the level of uric acid in the blood or urine. 

If too much uric acid is produced or not enough is excreted, it can accumulate in the body, causing increased levels in the blood (hyperuricemia). The presence of excess uric acid can cause gout, a condition characterized by inflammation of the joints due to the formation of uric acid crystals in the joint (synovial) fluid. Excess uric acid can also be deposited in tissues such as the kidney, leading to kidney stones or kidney failure.

The accumulation of too much uric acid is due to either increased production, decreased elimination, or a combination of both. Elevated levels of uric acid can occur when there is an increase in cell death, as seen with some cancer therapies or, rarely, as an inherited tendency to overproduce uric acid. Decreased elimination of uric acid is often a result of impaired kidney function due to kidney disease.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm. A 24-hour urine sample may be collected for the urine uric acid test.

Is any test preparation needed to ensure the quality of the sample?

No test preparation may be needed. Some institutions, however, recommend fasting for 4 or more hours. Follow any instructions provided and be sure to discuss with the health care provider any medications being taken before having this test performed.

The Test

How is it used?

The uric acid blood test is used to detect high levels of this compound in the blood in order to help diagnose gout. The test is also used to monitor uric acid levels in people undergoing chemotherapy or radiation treatment for cancer. Rapid cell turnover from such treatment can result in an increased uric acid level.

The uric acid urine test is used to help diagnose the cause of recurrent kidney stones and to monitor people with gout for stone formation.

When is it ordered?

The uric acid blood test is ordered when a health care provider suspects that someone has a high uric acid level. Some people with high levels of uric acid have a disease called gout, which is a common form of arthritis. People with gout suffer from joint pain, most often in their toes, but in other joints as well. The test is also ordered to monitor cancer patients undergoing chemotherapy or radiation therapy, to ensure that uric acid levels do not get dangerously high.

The urine uric acid test may be ordered when a person suffers from recurrent kidney stones or has gout and needs to be monitored for formation of these stones.

What does the test result mean?

Blood
Higher than normal uric acid levels in the blood is called hyperuricemia and can be caused by the over-production of uric acid in the body or the inability of the kidneys to adequately remove enough uric acid from the body. Further investigation is needed to determine the cause of the overproduction or decreased excretion of uric acid.

There are several genetic inborn errors that effect purine metabolism. Metastatic cancer, multiple myeloma, leukemias, and cancer chemotherapy can cause increased production of uric acid. Chronic renal disease, acidosis, toxemia of pregnancy, and alcoholism can cause decreased excretion.

Increased concentrations of uric acid can cause crystals to form in the joints, which can lead to the joint inflammation and pain characteristic of gout. Uric acid can also form crystals or kidney stones that can damage the kidneys.

The American College of Rheumatology published guidelines on the management of gout in 2012 that recommend that target serum urate (uric acid) levels should be below 6 mg/dL for people diagnosed with the condition.

Low levels of uric acid in the blood are seen much less commonly than high levels and are seldom considered cause for concern. Although low values can be associated with some kinds of liver or kidney diseases, Fanconi syndrome, exposure to toxic compounds, and rarely as the result of an inherited metabolic defect (Wilson disease), these conditions are typically identified by other tests and symptoms and not by an isolated low uric acid result.

Urine
High uric acid levels in the urine are seen with gout, multiple myeloma, metastatic cancer, leukemia, and a diet high in purines. Those at risk of kidney stones who have high uric acid levels in their urine may be given medication to prevent stone formation.

Low urine uric acid levels may be seen with kidney disease, chronic alcohol use, and lead poisoning.

Is there anything else I should know?

Many drugs can increase or decrease the level of uric acid. In particular, diuretic drugs like thiazide drugs can cause uric acid levels to go up.

Aspirin and other salicylates have varying effects on uric acid. At low aspirin levels (as may occur in persons taking aspirin only occasionally), aspirin can increase blood uric acid. On the other hand, in high doses (as may be used to treat rheumatoid arthritis), aspirin actually lowers the concentration of uric acid.

For people who have uric acid kidney stones or gout, foods that are high in purine content should be avoided, including organ meats (like liver and kidneys), sardines and anchovies. Alcohol also should be avoided, because it slows down the removal of uric acid from the body. Fasting, rapid weight loss, stress, and strenuous exercise all raise uric acid levels.

Although the uric acid test cannot definitively diagnose gout, a test for monosodium urate in synovial fluid (joint fluid) can.

Some people may have a high level of uric acid in the blood without having associated signs or symptoms (asymptomatic hyperuricemia). However, general screening to detect this condition is not recommended, nor is treatment considered appropriate.



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