Uric Acid (Synovial Fluid)

Synovial fluid analysis 

The synovial fluid uric acid test measures levels of uric acid that can collect in joint fluid. Uric acid is a normal body waste product. It forms when chemicals called purines break down. Purines are natural substances found in the body. They are also found in many foods, such as liver, shellfish, and alcohol. They can also be formed in the body when DNA is broken down. 

When purines break down into uric acid in the blood, the body gets rid of the acid when you urinate or have a bowel movement. But if your body makes too much uric acid, or if your kidneys aren't working well, uric acid can build up in the blood. Uric acid levels can also increase when you eat too many high-purine foods or take medicines such as diuretics, aspirin, or niacin. Then crystals of uric acid can form and collect in the joints. This causes painful inflammation. This condition is called gout. Uric acid can also lead to kidney stones.

If you have gout, you may have crystals of uric acid in your synovial fluid, the substance that surrounds joints. This fluid helps your joints move smoothly. 

You may need this test if you have symptoms of gout, such as:

• Joint pain or soreness

• Swelling and pain in a joint, such as the big toe, ankle, or knee

• Red skin around a joint

• Joints that are hot to the touch

• Swelling and pain that affects only 1 joint in the body

• Skin that looks shiny and is red or purple

You may also need this test if you have symptoms of kidney stones. Symptoms include:

• Severe pain along your lower back. This may repeatedly get worse and then get better. The pain may also travel to your genitals.

• Nausea

• Vomiting

• Urgent need to urinate

• Blood in your urine 

You may also have blood and urine tests to measure uric acid levels. Higher than normal levels of uric acid in the blood or urine can suggest gout. But the only way your healthcare provider can diagnose gout for sure is by measuring the levels of uric acid in your synovial fluid.

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your healthcare provider what your test results mean for you.

If your synovial fluid sample shows uric acid crystals, you may have gout. But even if your sample doesn't show uric acid crystals, you still may have gout. Crystals don't always form in the synovial fluid during a gout attack. 

This test needs a sample of synovial fluid. It's collected during a process called joint aspiration. To collect the fluid, your healthcare provider inserts a needle into the skin near an inflamed joint and withdraws some of the fluid into a vial or tube.

Joint aspiration has some minor risks. You may have bleeding in the area around the joint. Although rare, an infection can develop in the joint from the test. 

Some medicines may affect your test results. They include:

• Aspirin and other medicines that contain salicylate

• Cyclosporine, a medicine sometimes used for autoimmune diseases

• Levodopa, a medicine used to treat Parkinson disease

• Some diuretic medicines, such as hydrochlorothiazide

• Vitamin B-3 (niacin)

Other things that may affect your test results include:

• Vigorous exercise

• Chemotherapy or radiation therapy to treat cancer

• Foods high in purines, such as organ meats, mushrooms, some types of fish and seafood, and dried peas and beans 

Ask your healthcare provider about what to do before having this test. You may need to not eat or drink anything or not take certain medicines on the day of the test. Be sure your provider knows about all the medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illegal drugs you may use.