A serum filled blister represents which stage of pressure ulcer?

A serum-filled blister is characteristic of a Stage 2 pressure ulcer. In this stage, there is partial thickness loss of skin, which can manifest as a blister, abrasion, or a shallow open sore. The presence of the serum-filled blister indicates that the skin has been compromised and there is damage that extends into the epidermis, though not through the entire dermis. Stage 2 ulcers specifically involve the disruption of the skin's integrity, resulting in these types of fluid-filled blisters.

On the other hand, Stage 1 ulcers are characterized by non-blanchable erythema of intact skin, indicating there is still skin intact without open wounds. Stage 3 ulcers involve full thickness skin loss, where there may be visible fat, and sometimes can present with necrosis, but they do not typically involve blister formation. If a pressure ulcer is not classified within the existing stages, it would be referred to as not classified rather than indicating the presence of a blister. Thus, the correct classification of a serum-filled blister is Stage 2.