A uric acid blood test, also known as a serum urate measurement, determines the concentration of uric acid circulating in the bloodstream. This test helps healthcare providers evaluate how effectively the body is producing and eliminating this waste product. Results are often used to diagnose or monitor conditions like gout, a form of inflammatory arthritis, or to assess kidney function related to uric acid metabolism. The test also monitors patients undergoing cancer treatments, where rapid cell turnover can temporarily spike uric acid levels.
Do You Need to Fast for the Test?
In most cases, fasting is not required before a uric acid blood test, meaning you can typically eat and drink normally before the blood draw. However, the definitive instruction always comes from the healthcare provider or the laboratory, as requirements can vary. Some providers may recommend a short fast of about four hours for better accuracy. Fasting may also be necessary if the uric acid test is performed alongside other blood work, such as a lipid panel or glucose test, that mandates it.
It is recommended to avoid consuming purine-rich foods, such as organ meats, certain seafood, and alcohol, in the 24 hours leading up to the test. These foods can cause a temporary spike in uric acid levels, potentially skewing the results and presenting a falsely elevated reading. Maintaining normal water intake is encouraged to ensure hydration and aid in the blood draw process.
What the Uric Acid Test Measures
The uric acid test measures a natural waste product created when the body metabolizes purines, compounds found in all human cells and many foods. Purines are fundamental components of DNA and RNA. Uric acid is the end product when these compounds are broken down by the body, a metabolic process that is a continuous part of cell turnover and digestion.
After production, most uric acid dissolves in the blood and is transported to the kidneys. The kidneys filter this dissolved uric acid from the bloodstream and excrete the majority of it through the urine. The blood test evaluates the balance between the amount of uric acid produced and the amount eliminated by the kidneys. If the body produces too much or the kidneys excrete too little, the concentration in the blood rises.
Interpreting High and Low Uric Acid Levels
An elevated level of uric acid in the blood is known as hyperuricemia, which is the main risk factor for developing gout. When concentrations exceed the physiological saturation threshold, typically above 6.0 milligrams per deciliter (mg/dL), the substance can crystallize. These needle-shaped crystals, called monosodium urate, deposit in and around the joints. This commonly affects the big toe, triggering the intense pain and inflammation characteristic of a gout flare.
Hyperuricemia results from two primary causes: the overproduction of uric acid or under-excretion by the kidneys. Conditions like kidney disease, which impairs the filtering process, can lead to high levels. Certain types of cancer treatments that cause rapid cell death and release large amounts of purines also contribute. For individuals diagnosed with gout, a therapeutic target level below 6.0 mg/dL is often set to prevent new crystal formation and allow existing crystals to dissolve.
Low uric acid levels, known as hypouricemia, are much less common and typically less of a direct health concern than high levels. A low result may suggest underlying issues, including certain liver conditions or rare inherited disorders. Specific kidney disorders, like Fanconi syndrome, can also cause low blood levels because the kidneys excrete too much uric acid into the urine.
Medications and Other Factors Affecting Accuracy
Many factors beyond food and drink can temporarily alter uric acid levels, potentially leading to inaccurate test results. Certain prescription drugs interfere with the body’s handling of uric acid. These include diuretics, or “water pills,” which reduce the kidneys’ ability to excrete it. Low-dose aspirin and niacin (Vitamin B-3), often used for cholesterol management, can also elevate serum urate concentrations.
Strenuous exercise just before the blood draw can cause a temporary rise in uric acid levels. Excessive alcohol consumption should be avoided prior to the test, as it increases uric acid production and interferes with its excretion. It is important to disclose all medications, including over-the-counter drugs and supplements, to the healthcare provider, who may advise a temporary pause before the test.