Diagnosis of Gangrene
Tests used to help make a diagnosis of gangrene include:

Blood tests. An abnormally elevated white blood cell count often indicates the presence of an infection. Your doctor might also perform blood tests to look for the presence of certain bacteria or other germs.

Imaging tests. An X-ray, a computerized tomography (CT) scan or a magnetic resonance imaging (MRI) scan can be used to view interior body structures, such as your internal organs, blood vessels or bones, and assess the extent to which gangrene has spread. These types of tests can also help your doctor see any gas that is present under your skin.

An arteriogram is an imaging test used to visualize your arteries. During this test, dye is injected into your bloodstream and X-ray pictures are taken to determine how well blood is flowing through your arteries. An arteriogram can help your doctor find out whether any of your arteries are blocked.

Surgery. Surgery may be performed to determine the extent to which gangrene has spread within your body.

Fluid or tissue culture. A culture of the fluid from a blister on your skin may be examined for the bacterium Clostridium perfringens, a common cause of gas gangrene, or your doctor may look at a tissue sample under a microscope for signs of cell death.