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Joint fluid culture

Definition

Joint fluid culture is a laboratory test to detect infection-causing germs in a sample of fluid surrounding a joint.

How the Test is Performed

A sample of joint fluid is needed. This may be done in a doctor'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 laboratory. There, it is placed in a special dish and watched to see if bacteria or fungi grow. This is called a culture.

If these germs are detected, other tests may be done to further identify the infection-causing substance and its sensitivities or resistance to different antibiotics and determine the best treatment.

How to Prepare for the Test

Your health care 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.

How the Test will Feel

Sometimes, the provider will first inject numbing medicine into the skin with a small needle, which will 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.

Why the Test is Performed

Your provider may order this test if you have unexplained pain and inflammation of a joint or a suspected joint infection.

Normal Results

The test result is considered normal if no organisms (bacteria or fungi) grow in the laboratory dish.

What Abnormal Results Mean

Abnormal results are a sign of infection in the joint. Infections may include:

• Bacterial arthritis

• Fungal arthritis

• Gonococcal arthritis

• Tuberculous arthritis

Risks

Risks of this test include:

• Infection of the joint -- unusual, but more common with repeated aspirations

• Bleeding into the joint space

References

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, synovial, serous body fluids, and alternative specimens. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 30.

Review Date: 12/4/2022

Reviewed By: Jatin M. Vyas, MD, PhD, Associate Professor in Medicine, Harvard Medical School; Associate in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.