Classifying or Staging Pressure Ulcers

The skin comprises two separate layers, the epidermis and the dermis. The epidermis is the thin, tough outside layer of the skin.  The epidermis is avascular (contains no blood vessels) and regenerates itself about every month. The dermis is the thick, inside layer of skin that attaches to the underlying tissue and gives the skin strength and flexibility. The dermis contains hair follicles. The main functions of the skin, including the hair follicles, are to maintain fluid and electrolyte balance, to act as a protective barrier from infection, to maintain temperature of the body, and to provide sensation. 

When pressure ulcers develop, they are graded based on the degree of damage to the tissue. The European Pressure Ulcer Advisory Panel and the National Pressure Ulcer Advisory Panel (EPUAP/NPUAP, 2009; NPUAP, 2007) classifies pressure ulcers based on the depth of the wound.

Category/Stage I:
In people with lighter skin tones, the area appears red area and, when pressed, does not turn white. In people with darker skin tones, the area may appear red, blue, or purple. The area may be painful and warmer or cooler than the skin around it.


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Category/Stage II:
There is partial thickness loss of dermis. The outer layer of skin blisters or forms a shallow, open sore with a red pink wound bed without slough. It may look like a blister.


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Category/Stage III:
There is full-thickness tissue loss. The tissue below the skin is damaged and the sore looks like a shallow crater. Subcutaneous fat might be visible, but bone, tendon, and muscle are not.


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Category/Stage IV:
There is full-thickness tissue loss. The crater becomes deep enough to see bone, tendon, or muscle. You may also see slough and eschar.


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Unstageable/Unclassified:
There is full thickness tissue loss and the base of the ulcer is covered by slough (yellow, tan, gray, green, or brown) and/or eschar (tan, brown, or black).  Until the slough or eschar is removed, the stage of the pressure ulcer cannot be determined.


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Suspected Deep Tissue Injury: 
Purple or maroon localized area of discolored intact skin, or blood-filled blister due to damage of underlying soft tissue from pressure and/or shear.


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Illustrations presented with permission from the NPUAP.

Pressure ulcers show 'redness' differently based on the patient's skin tone. A Category/Stage I pressure ulcer in patients with light skin may look red, but in patients with darker skin may look red, blue, or purple. Therefore, special attention should be given to patients with dark skin as pressure ulcers may be more difficult to detect. A natural or halogen source of light should be used to assess pressure ulcers.

Pressure ulcers do not heal from a Category/Stage IV to a Category/Stage I, so staging cannot be reversed.

For more information, please visit the NPUAP's website