Final answer:
The Physical Status modifier for patients of extreme age is -P4, used in anesthesia coding.
Step-by-step explanation:
The Physical Status modifier that refers to patients of extreme age is -P4. This modifier is typically used in anesthesia coding to indicate that the patient is at a higher risk due to age-related factors. In anesthesia billing, the Physical Status modifiers are used to communicate the complexity of the service provided, based on the patient's condition at the time anesthesia is administered. Modifier -P4 is specifically used for patients who are considered to be at an extreme age, typically very young (neonates) or elderly patients, which may contribute to the complexity of their anesthesia care.