Synovial fluid analysis is also known as joint fluid analysis. It helps diagnose the cause of joint inflammation.

Each of the joints in the human body contains synovial fluid. This fluid is a thick liquid that lubricates the joint and allows for ease of movement. In joint diseases like arthritis, the synovium of the joint is the main place where inflammation occurs.

Limited mobility in the joint, or pain and stiffness with movement, are often the first signs of joint disorders. Joint inflammation is more common as you age.

A synovial fluid analysis is performed when pain, inflammation, or swelling occurs in a joint, or when there’s an accumulation of fluid with an unknown cause. Taking a sample of the fluid can help diagnose the exact problem causing the inflammation. If the cause of the joint swelling is known, a synovial fluid analysis or joint aspiration may not be necessary.

Some potential diagnoses include infection, gout, arthritis, and bleeding. In some cases with excess fluid, simply removing some fluid can help relieve pain in the affected joint.

Sometimes synovial fluid analysis is used to monitor people with known joint disorders.

Your doctor will recommend a synovial fluid analysis if you have signs of joint inflammation, redness, swelling, or injury to help diagnose the condition.

You won’t need to do anything in preparation for the test, but let your doctor know if you’re taking blood thinners. They can affect results.

The synovial sampling process will be done at your doctor’s office. This process doesn’t require any incisions and will only take a couple of minutes. Your doctor will clean the area and prepare it for injections. If you’re getting anesthesia, your doctor will inject it into the site to limit pain and discomfort.

Once the area has been numbed, your doctor will insert a larger needle into the joint and draw fluid into the syringe. This process of removing fluid from a joint is called arthrocentesis.

Your doctor will send the fluid sample to the laboratory for examination. A lab technician will look at the color and thickness of the fluid and assess red and white blood cells under a microscope.

The technician will also look for crystals or signs of bacteria and measure:

  • glucose
  • proteins
  • uric acid
  • lactic dehydrogenase (an enzyme that increases in cases of inflammation and tissue damage)

The fluid sample will also be cultured to test for bacteria.

What to expect

A synovial fluid analysis may be mildly uncomfortable, but the whole process lasts only a few minutes. You might receive a local anesthesia to numb the area. You may feel a prick and burning sensation from the anesthesia at the site of entry.

A larger needle will then be inserted into the joint to withdraw the synovial fluid. If you receive anesthesia, you should feel minimal discomfort. If you don’t receive anesthesia, the needle may cause slight pain and discomfort. You might feel pain if the tip of the needle touches bone or a nerve.

Following the procedure, apply ice to reduce any pain or swelling.

Normal synovial fluid is straw-colored, clear, and slightly sticky or stringy.

Abnormal synovial fluid may be cloudy and thicker or thinner than normal fluid. Cloudiness could mean there are crystals, excess white blood cells, or microorganisms in the fluid.

If you have gout, the fluid will contain crystals. Less stringiness in the fluid could signal inflammation. Excess fluid in the joint could be a predictor of osteoarthritis. Reddish-colored fluid could mean blood is present.

Blood in the fluid could point to a bleeding injury in the joint or a more serious bleeding problem throughout the body, such as hemophilia. Absent or ineffective clotting factors cause hemophilia.

Cloudy fluid, blood in the fluid, or excess fluid are all signs of a problem in or around the joint, such as:

  • gout
  • arthritis
  • infection
  • autoimmune disorders
  • injury to the joint

This procedure is highly effective in diagnosing gout by identifying crystals in the fluid.

A synovial fluid test carries minimal risks. The most common risks are bleeding or infection in the joint. It’s normal to experience soreness or stiffness in the joint. Complications from this procedure are rare.