Joint fluid Gram stain

A sample of joint fluid is needed. This may be done in a health care provider's office using a needle, or during an operating room procedure. Removing the sample is called joint fluid aspiration . The fluid sample is sent to a lab where a drop of fluid is spread in a very thin layer onto a microscope slide. This is…

Your provider will tell you how to prepare for the procedure. No special preparation is needed. But, tell your provider if you're taking a blood thinner, such as aspirin, warfarin (Coumadin) or clopidogrel (Plavix). These medicines can affect test results or your ability to take the test.

Sometimes, the provider will first inject numbing medicine into the skin with a small needle, which may sting. A larger needle is then used to draw out the synovial fluid. This test may also cause some discomfort if the tip of the needle touches bone. The procedure usually lasts less than 1 to 2 minutes.

The test is performed when there is unexplained swelling, joint pain , and inflammation of a joint, or to check for suspected joint infection.

A normal result means no bacteria are present on the Gram stain.

Abnormal results mean bacteria were seen on the Gram stain. This may be a sign of a joint infection, for example, gonococcal arthritis due to bacteria called Neisseria gonorrhoeae or arthritis due to bacteria called Staphylococcus aureus .

Risks of this test include: Infection of the joint -- unusual, but more common with repeated aspirations Bleeding into the joint space

El-Gabalawy HS, Tanner S. Synovial fluid analyses, synovial biopsy, and synovial pathology. In: Firestein GS, Budd RC, Gabriel SE, Koretzky GA, McInnes IB, O'Dell JR, eds. Firestein & Kelly's Textbook of Rheumatology . 11th ed. Philadelphia, PA: Elsevier; 2021:chap 56. Karcher DS, McPherson RA. Cerebrospinal,…