Wound staging is a standardized system healthcare professionals use to classify the severity and extent of tissue damage, most commonly applied to pressure injuries. This classification provides a common language for documenting the injury and tracking its progression. Assigning a stage assesses how deeply the injury has penetrated the layers of the skin and underlying tissues. The stage guides the selection of appropriate treatments and helps predict the potential healing timeframe.
Essential Criteria for Wound Assessment
Before a stage can be accurately assigned, a precise assessment of the wound’s characteristics must be completed. Initial evaluation requires measuring the size of the wound, including its length, width, and depth, typically recorded in centimeters. For irregularly shaped wounds, a consistent clock-face method is used to ensure measurements are taken from the longest points and to note any tunneling or undermining beneath the skin’s surface.
The type of tissue visible within the wound bed offers insight into the healing process and is categorized as either viable or non-viable. Viable tissue includes bright, red granulation tissue, which signals healthy new growth, or pink epithelial tissue forming at the edges. Non-viable tissue consists of yellow or tan slough (soft, dead tissue) or black, leathery eschar (hard, necrotic tissue).
Observing the wound’s drainage, known as exudate, involves noting its amount, color, and consistency. Exudate can range from clear, watery serous fluid to thicker, pus-like purulent discharge, which suggests a potential infection. Signs of a local infection, such as increased warmth, redness, swelling, or a foul odor, must also be documented as they influence the treatment approach.
The Four Stages of Wound Severity
The traditional staging system describes a progression of tissue damage, primarily used to classify pressure injuries. A Stage 1 injury involves intact skin with an area of localized, non-blanchable redness. This means the color remains red or darker even when pressure is applied. This initial stage may also present with changes in skin temperature, firmness, or sensation, but there is no break in the skin’s surface.
A Stage 2 injury represents partial-thickness skin loss, damaging the epidermis and potentially part of the dermis layer. This open wound appears as a shallow ulcer with a pink or red wound bed, but it does not expose deeper fat or tissue. The injury may also present as an intact or ruptured serum-filled blister. Stage 2 wounds do not contain slough, eschar, or granulation tissue, distinguishing them from deeper injuries.
The damage progresses to a Stage 3 injury when there is full-thickness skin loss, extending through the dermis and into the underlying subcutaneous fat layer. Fat tissue may be visible in the base of this deeper, crater-like ulcer. Slough or eschar may be present, but it does not obscure the full extent of the tissue loss. Neither muscle, bone, nor tendon is exposed, which separates it from the most severe category.
The final classification is a Stage 4 injury, which involves full-thickness tissue loss with exposed bone, tendon, ligament, or muscle. Slough or eschar may be visible. The wound often includes undermining (tissue loss parallel to the skin surface) or tunneling (a narrow channel extending from the wound). This deep tissue damage can involve structures like the joint capsule, making complications such as bone infection a serious concern.
Special Classifications for Complex Wounds
Some wounds cannot be categorized using the sequential Stage 1 through 4 system, requiring special classifications to convey their severity. Unstageable wounds are full-thickness injuries where the actual depth of tissue loss is unknown because the wound base is entirely obscured by non-viable material. This material is typically a layer of slough (yellow, tan, or green) or an area of black or brown eschar.
The severity of an unstageable wound is high, as removing the non-viable covering will almost certainly reveal a Stage 3 or Stage 4 injury underneath. A specific stage cannot be assigned until a healthcare provider removes enough of the slough or eschar to visualize the true depth. An exception is stable, dry eschar on an ischemic limb or the heel, which is often left intact to serve as a natural biological cover.
Another category is the Deep Tissue Injury (DTI), which involves significant damage to the underlying soft tissue beneath intact or discolored skin. A DTI appears as a localized area of purple or maroon discoloration, or as a blood-filled blister. It results from prolonged pressure or shear forces at the bone-muscle interface. The visible surface damage is minimal compared to the deep tissue destruction, which may rapidly progress to expose further layers of tissue.
For acute wounds not caused by pressure, such as lacerations or abrasions, severity is often described using the general depth descriptors of “partial thickness” or “full thickness.” Partial thickness refers to injuries that penetrate only the epidermis and part of the dermis. Full thickness indicates the damage extends through all layers of the skin. This non-numerical method provides a straightforward description for injuries that do not fit the pressure injury staging criteria.