Overview & Description

A culture of joint fluid, or aspirate, can identify bacteria or organisms in joint fluid that may be causing an infection in a particular joint. The test is normally done when a joint is swollen, painful, or appears to be infected.

Who is a candidate for the test?

This test is normally performed to help diagnose arthritis, or an infection or tumor in a joint.

How is the test performed?

First, a sample of fluid is taken from the swollen joint. A sterile needle is inserted through the skin into the joint. A small amount of fluid is withdrawn from the joint. This sample is then taken to the laboratory for testing. Usually, the fluid is then placed on special culture media to see if bacteria or other microorganisms will grow.

Preparation & Expectations

What is involved in preparation for the test?

A person should request specific instructions from his or her health care provider.

Results and Values

What do the test results mean?

Fluid in a joint is usually sterile. This means that no microorganisms are present. If the joint fluid contains microorganisms, such as bacteria or fungi, they will grow in culture in the laboratory. This allows a microbiologist to identify the microorganisms and design a course of therapy to treat the infection. For example, a bacterial infection may be treated with antibiotics.