Diagnosis

The following tests typically help diagnose septic arthritis:

• Joint fluid analysis. Infections can alter the color, consistency, volume and makeup of the fluid within your joints. A sample of this fluid can be withdrawn from your affected joint with a needle. Laboratory tests can determine what organism is causing your infection, so your doctor will know which medications to prescribe.
• Blood tests. These can determine if there are signs of infection in your blood. A sample of your blood is removed from a vein with a needle.

• Imaging tests. X-rays and other imaging tests of the affected joint can assess damage to the joint or loosening of an artificial joint.

  A specialized scan that involves swallowing or injecting a small amount of a radioactive chemical may be used if your doctor suspects you have a prosthetic joint infection and it's been more than a year since you've had surgery.