Modifier P1 indicates an ASA Physical Status I — a normal healthy patient — and is appended to anesthesia CPT codes (00100–01999) based on the anesthesiologist’s clinical assessment. It documents the patient’s pre‑anesthesia health status but carries zero modifying units. For Medicare and many plans that do not recognize physician physical status in the anesthesia payment formula, P1 does not change reimbursement. When private payers recognize physical status modifiers, many contracts accept P1 but it still adds 0 modifying units and therefore does not increase payment.

Use P1 only when the patient truly meets ASA I criteria (healthy, non‑smoker, minimal alcohol use, no systemic disease). Append it to the appropriate anesthesia CPT code to support documentation of risk level; it is principally a documentation tool rather than a mechanism to obtain additional payment. Always verify individual payer policy because recognition of physical status modifiers varies between Medicare, Medicare Advantage, and private insurers.

Practical billing examples illustrate that P1 contributes 0 modifying units. For a private payer that recognizes physical status modifiers, total anesthesia units would include base units and time units plus 0 units for P1. Under Medicare (and many Medicare Advantage plans), physical status modifiers are not recognized for payment, so appending P1 does not affect the allowed amount.