What is a synovial fluid analysis?

Synovial fluid, also known as joint fluid, is a thick liquid located between your joints. The fluid cushions the ends of bones and reduces friction when you move your joints. Synovial fluid analysis is a group of tests that checks for disorders that affect the joints. The tests usually include the following:

• An exam of physical qualities of the fluid, such as its color and thickness
• Chemical tests to check for changes in the fluid's chemicals
• Microscopic analysis to look for crystals, bacteria, and other substances

Other names: joint fluid analysis

What is it used for?

Synovial fluid analysis is used to help diagnose the cause of joint pain and inflammation. Inflammation is the body's response to injury or infection. It can cause pain, swelling, redness, and loss of function in the affected area. Causes of joint problems include:

• Osteoarthritis, the most common form of arthritis. It is a chronic, progressive disease that causes joint cartilage to break down. It can be painful and lead to loss of mobility and function.
• Gout, a type of arthritis that causes inflammation in one or more joints, usually in the big toe
• Rheumatoid arthritis, a condition in which the body's immune system attacks healthy cells in your joints
• Joint effusion, a condition that happens when too much fluid builds up around a joint. It often affects the knee. When it affects the knee, it may be referred to as knee effusion or fluid on the knee.
• Infection in a joint
• Bleeding disorder, such as hemophilia. Hemophilia is an inherited disorder that can cause excessive bleeding. Sometimes the excess blood ends up in the synovial fluid.

Why do I need a synovial fluid analysis?

You may need this test if you have symptoms of a joint disorder. These include:

• Joint pain
• Joint swelling
• Redness at a joint
• Joint that feels warm to the touch

What happens during a synovial fluid analysis?

Your synovial fluid will be collected in a procedure called arthrocentesis, also known as joint aspiration. During the procedure:

• A health care provider will clean the skin on and around the affected joint.
• The provider will inject an anesthetic and/or apply a numbing cream to the skin, so you won't feel any pain during the procedure. If your child is getting the procedure, he or she may also be given a sedative. Sedatives are medicines that have a calming effect and help reduce anxiety.
• Once the needle is in place, your provider will withdraw a sample of synovial fluid and collect it in the syringe of the needle.
• Your provider will put a small bandage on the spot where the needle was inserted.
• The procedure usually takes less than two minutes.

Will I need to do anything to prepare for the test?

You may need to fast (not eat or drink) for several hours before the test. Your health care provider will let you know if you need to fast and if there are any special instructions to follow.

Are there any risks to the test?

Your joint may be sore for a couple of days after the procedure. Serious complications, such as infection and bleeding may happen, but are uncommon.