This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
Non blanchable erythema of skin is classified as which stage of decubitus ulcer? 
Select and explain. 
A. Stage I, B. Stage II, C. Stage III, D. Stage IV
A: Stage I
Answer: A: Stage I 
Explanation: The four stages of pressure ulcer formation are as follows: Stage I, nonblanchable erythema of intact skin; Stage II, paial-thickness skin loss involving epidermis or dermis, or both; Stage III, full-thickness skin loss, but not through the fascia; and Stage IV, full-thickness skin loss with extensive involvement of muscle and bone. Ref: Schwaz's principle of surgery 9th edition, chapter 9.