How is frostbite diagnosed?

Once at a medical facility, frostbite injuries are not likely to be classified (by stage and degree) initially as it can be very difficult to determine whether the damage is superficial or deep, as well as the extent of tissue injury during an initial medical evaluation.

The priority will be to rewarm the affected person appropriately (thawing the affected skin / tissues), after which the extent of injured tissue can generally be assessed. A medical team will also assess the patient for any signs of hypothermia upon arrival, which if present, will require immediate assistance before any symptoms of frostbite are directly attended to. Signs of dehydration will also be treated swiftly so as to avoid further adverse or life-threatening complications.

The diagnostic process for frostbite

The process for diagnosing frostbite begins with a physical examination of the affected areas. If a person is conscious and reasonably alert, a doctor will ask specific questions relating to the possible causes of cold exposure which brought on frostbite. He or she will want to determine the type of cold exposure and its duration.

A doctor will look carefully at the skin and check for any obvious signs that may indicate the specific stage of injury progression. Signs and symptoms, however, may not be entirely obvious during the examination until the affected areas are effectively thawed.

While re-warming is taking place, a doctor may recommend some testing procedures to help with determining the severity of injury, as well as noting the affected person’s temperature, blood pressure level, pulse and respiratory rate. Tests may include blood samples for analysis (this can help to check for or determine complications of infection) and image screenings (such as an MRI / magnetic resonance imaging scan, an X-ray, scintigraphy or bone scan) if the treating doctor regards a person’s condition as potentially severe. Imaging tests may be useful for determining the severity of tissue injury, as well as aid in assessing whether deeper structures, such as the muscle and bone, have sustained any damage, as well as identify any signs of possible infection.

X-rays can show soft tissue swelling, but cannot assist a doctor in distinguishing viable from non-viable tissues. Using radiographs from the screening, a doctor is more likely to check for any trauma-related injuries, such as a dislocation or fracture which may have taken place.

A doctor may also perform an angiography which will check for signs of slowing blood flow and may be useful for predicting a pattern of possible ischemia (when the heart muscle does not receive enough oxygenated blood, due to constriction or blockages within the arteries).

Scintigraphy (a radioactive tracer) is potentially useful for assessing the response of damaged tissues in relation to re-warming or thawing treatments. Bone scans may also be recommended in the weeks following initial treatment as part of follow-up monitoring of a person’s condition.

Once controlled re-warming takes place, clear blisters may form within 48 hours, indicating a mild case of frostbite. Blister formations filled with blood or a cloudier fluid around the same time period are usually indicative of deep / severe frostbite (third-stage frostbite).

Using all data collected during a physical evaluation and testing procedures, a doctor will note a diagnosis of either superficial or deep frostbite (and the degree of injury). He or she will also determine a suspected (initial) prognosis (outlook) for a person’s condition. If sensation is intact, the formation of blisters contains clear fluid, and skin is soft and palpable, and returns to its normal colour (or pink when thawed), a prognosis is likely to be reasonably good.

If during thawing, blister formations appear to contain dark, cloudy or bloody fluid, and the skin layers show extensive damage discolouration (dark and hard – skin necrosis or gangrene), the prognosis will generally not be good. Other signs and symptoms that may be noted during re-warming which may indicate deep / severe frostbite and include:

• Joint pain
• A pallor or blue discolouration of the skin
• Excessive sweating
• Hyperaemia (signs of excess blood in blood vessels)

The stage degree of damage may be assessed as follows:

• First-degree (superficial): Lack of physical sensation, cold sensitivity, numb and pale areas surrounded by rings of hyperaemia and mild swelling.
• Second degree (superficial): Clear blister formations (which may also contain the hormone thromboxane and prostaglandin compounds), full-thickness skin freezing and a hardened outer layer of skin (soft, resilient tissue beneath), as well as substantial swelling. Cold sensitivity may also be persistent.
• Third degree (deep / severe): Deeper skin layer freezing (subdermal plexus freezing), haemorrhagic blister formations (often containing blood), blue or grey skin discolouration (cyanosis), severe pain (or burning) once affected tissues are thawed / re-warmed, and thick gangrenous wound (eschar) formations (ulcerations).
• Fourth degree (deep / severe): Signs of damage to the deeper tissues (tendons, nerves, muscle and bone), skin that is frozen and hard, tissues beneath the skin that are also frozen and hard, mottled tissue appearance (which becomes dry, darkened and ‘mummified’), and extensive swelling (oedema).

Further superficial and deep / severe frostbite characteristics will involve:

• Superficial: Injury appears to only affect the outermost skin layers and subcutaneous tissues (just beneath the skin) which are pliable. A patient experiences numbness at the start of rewarming treatment which gives way to stinging and burning sensations once thawing has taken effect. Neurovascular function will also return to normal. Tissue loss (necrosis) is not evident (or is very minimal).
• Deep / severe: Injury appears to affect the skin, subcutaneous tissues, tendons, nerves, muscles and bone structures. Skin layers do not appear to ‘roll over’ bony structures. Rewarming processes do not appear to restore sensation, or improve mottled and pulseless tissues, nor increase the flexibility function or deeper tissues (such as muscles). Tissue loss is prominent.