Joint Fluid Analysis

Test Overview

Joint fluid analysis is a test to look at joint fluid under a microscope for problems such as infection, gout, pseudogout, inflammation, or bleeding. The test can help find the cause of joint pain or swelling.

Normally, only a small amount of joint fluid is found in a joint. Joint fluid acts as a lubricant for the joint and cushions joint structures. If you have a joint problem, you may have more fluid in your joint and your joint may become swollen, stiff, and painful.

A sample of joint fluid can be taken from any joint in your body. The joint fluid is then analyzed in a lab to look for a bacterial infection, gout, pseudogout, or bleeding.

Why It Is Done

Joint fluid analysis is done to:

• Find infection, gout, or pseudogout.
• Relieve pain caused by the buildup of fluid in your joint.

After removing the joint fluid, your doctor may give you medicine, such as corticosteroids, into the joint to help keep fluid from building back up.

How To Prepare

Tell your doctor if you:

• Have taken aspirin recently.
• Are taking any medications that can delay blood clotting, including nonsteroidal anti-inflammatory drugs (NSAIDs, such as ibuprofen, naproxen, or etodolac) or warfarin (Coumadin).
• Are allergic to any medications, including anesthetics.
• Have any bleeding problems.
• Are or might be pregnant.

Talk to your doctor about any concerns you have about the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).

How It Is Done

Joint fluid analysis takes about 20 minutes and can be done in your doctor's office, clinic, operating room, or emergency room. Depending on which joint will be examined, you may be asked to undress and put on a hospital gown. You will sit or lie down on an examining table.

Your doctor will examine the joint to determine where the needle should be inserted. The skin over the joint area will be cleaned with antiseptic solution. A local anesthetic is often injected into the skin over the joint. For young children, a sedative may also be given.

A long, thin needle is slowly inserted in the joint area. A syringe attached to the needle is used to remove a sample of joint fluid. Samples of the fluid may be put in special tubes or containers and sent to the lab. A cortisone shot may be given into the joint before the needle is removed.

A tight (pressure) bandage will be placed over the site to reduce swelling and bruising. An elastic bandage may also be wrapped around your joint, such as your knee, to reduce swelling.

How It Feels

You will feel a prick or sting when the anesthetic is given. You may feel tingling, pressure, pain, or fullness in your joint as the fluid is removed.

Risks

There is very little chance of having a problem after a joint fluid analysis. Infection, bleeding, or damage to the tendon, nerve, or joint is rare.

Sometimes your doctor may not be able to draw any fluid out. The joint space may be too small, you may have scar tissue in the joint space, or there may not be any fluid in the joint.

The joint may be sore for 1 to 2 days after the procedure. If you have a cortisone shot, you may have some soreness or irritation at the site of the shot for 1 to 2 days. Avoid strenuous use of the joint for 2 to 3 days.

Results

Joint fluid analysis is a test to look at joint fluid under a microscope for problems such as infection, gout, pseudogout, inflammation, or bleeding. The test can help find the cause of joint pain or swelling.

The results of a joint fluid analysis are usually available the same day. The results from a culture are usually available in a few days.

Abnormal values

• Color and clarity. Slightly cloudy fluid may be caused by inflammation, gout, or pseudogout. A deep, dark red color may be caused by bleeding in the joint. Milky white may be caused by infection or inflammation.
• Blood cell count. Large numbers of red blood cells may be caused by bleeding in the joint from injury, inflammation, or abnormal clotting of the blood. Large numbers of white blood cells may be caused by gout, pseudogout, other types of arthritis (such as rheumatoid arthritis), psoriatic arthritis, injury, or infection.
• Presence of crystals. Uric acid crystals in the joint is caused by gout. Calcium pyrophosphate crystals are caused by pseudogout.
• Gram stain and culture. Bacteria seen under a microscope on the Gram stain (a special dye) of the joint fluid may be caused by an infection. Bacteria that grows out of a culture plate in 1 to 2 days confirms the presence of an infection.

What Affects the Test

You may not be able to have this test or the results may not be useful if:

• You do not have enough fluid in the joint space.
• You have an infection in the skin near the joint.

What To Think About

• Your doctor may recommend further treatment with medicine, physical therapy, or surgery after the cause of your joint pain has been found.
• If you have a skin infection near the surface area of the joint, the infection may spread to the joint during the procedure. However, since skin redness in this area may be caused by gout or a joint infection, your doctor may feel that the benefits of a joint fluid analysis outweigh the risks. In this case, you may be given antibiotics to help prevent a joint infection.
• Tissue from the joint lining may be removed during this test (synovial biopsy). The tissue sample is then examined under a microscope.