Joint fluid gram stainDefinition: Joint fluid gram stain is a laboratory test to identify bacteria in a sample of joint fluid using a special series of stains (colors). The gram stain method is one of the most commonly used methods to rapidly diagnose bacterial infections.
Alternative Names: Gram stain of joint fluid
How the test is performed: A sample of joint fluid is needed. For information on how this procedure is done, see joint fluid aspiration . The fluid sample is sent to a lab where a small drop is placed in a very thin layer onto a microscope slide. This is called a smear. Several different colored stains are applied to the sample. The laboratory personnel will look at the stained smear under a microscope to see if bacteria are present. The color, size, and shape of the cells help identify the bacteria.
How to prepare for the test: For information on how to prepare for the removal of joint fluid, see joint fluid aspiration .
How the test will feel: For information on how it will feel when the joint fluid is removed, see joint fluid aspiration .
Why the test is performed: The test is performed when there is unexplained swelling, joint pain , and inflammation of a joint, or to check for suspected joint infection.
Normal Values: A normal result means no bacteria are present on the gram stain. Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
What abnormal results mean: Abnormal results mean bacteria were seen on the gram stain. This may be a sign of a joint infection (for example, gonococcal arthritis ).
What the risks are: There is no risk to the patient associated with a gram stain. For information regarding risks related to the removal of joint fluid, see joint fluid aspiration .
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