health

Diagnosis is usually made in the field on the basis of the appearance
of the frostbitten parts of the body. Some doctors use a four-degree
classification of injuries:

• First-degree: The epidermis (outermost layer of the skin) is reddened,
  swollen, and may look waxy. There is also a loss of sensation in
  the affected skin.
  
• Second-degree: The skin is reddened, swollen, and has formed blisters filled
  with a clear or milky fluid.
• Third-degree: The blisters are filled with blood and the skin begins
  to turn black.
  
• Fourth-degree: The epidermis, dermis, and underlying muscles,
  tendons, and bones are damaged.

A technique that can be used to diagnose the extent of soft-tissue
injury after frostbite is technetium scintigraphy. This is a technique in
which radioactive technetium is administered intravenously. The radioactive
element is taken up differently by healthy and damaged tissue, and
the pattern of “hot spots” and “cold spots” as traced by a scanner allows
the doctor to tell whether and where deep tissues have been damaged by
frostbite. Scintigraphy can also be used to monitor the recovery of the
injured tissues following emergency treatment.
X rays and other imaging studies will not help in diagnosing frostbite
but may be used to evaluate the injured person for broken or fractured
bones.