A person with necrotizing fasciitis usually is very sick by the time he or she sees a doctor. The person is likely to need immediate treatment-for shock or organ failure-before any test results are available.

Tests used to evaluate a person with possible necrotizing fasciitis may include:

• Routine blood tests, such as complete blood count (CBC), blood chemistry, creatine phosphokinase (CPK), and C-reactive protein. Test results can help show whether an infection is present or if muscles deep in the body have been damaged.
• Skin and wound cultures, which are often obtained during surgery, to determine what kind of bacteria are causing the infection. Fluid and material from the wound can be stained with special chemicals or dyes to quickly identify the type of bacteria.
• Chest X-rays, to look for signs of lung damage (respiratory distress syndrome).
• Other X-rays, to check for gas or fluid buildup at the site of the infection.

A CT scan or magnetic resonance imaging (MRI) is sometimes done when the diagnosis is uncertain or to help determine the depth of the infection.

If necrotizing fasciitis is suspected, surgical removal of the infected tissue is usually necessary both to confirm the diagnosis and to stop the spread of infection.

The person may need other tests, depending on the part of the body affected by the infection and what problems it is causing.