Physiological Systems (4A) ICD-10-PCS
The 4A body system covers Measurement and Monitoring procedures on physiological systems, with 418 ICD-10-PCS codes across 2 root operations, 416 of them billable in fiscal year 2027. Each root operation defines a distinct procedural objective, and the info icons show the official definition with a preview of the codes inside.
Root Operations in This Body System 2 operations · 418 codes
| Chars 1–3 | Root Operation | Codes | Billable |
|---|---|---|---|
| 4A0 | MeasurementDetermining the level of a physiological or physical function at a point in time | 223 | 222 |
| 4A1 | MonitoringDetermining the level of a physiological or physical function repetitively over a period of time | 195 | 194 |
The info icon shows the official root operation definition and previews the codes in that range.
About the 4A Body System
These codes describe checking physiological or physical functions in body systems such as cardiac, respiratory, urinary, and nervous. The fourth character identifies the system, separating central from peripheral nervous and arterial from venous.
Measurement determines a function’s level at a point in time. Monitoring checks its level repeatedly over time.
FY 2027 changes: The FY 2027 ICD-10-PCS update, effective October 1, 2026, added 1 code in this body system. Table with changes: 4A0 Measurement.
Questions About This Page
How many codes are in the 4A body system?
The 4A body system contains 418 ICD-10-PCS codes in FY 2027, organized into 2 root operations. 416 of them are billable on inpatient claims.
What is a root operation?
The root operation is the third character of every ICD-10-PCS code and names the objective of the procedure. Drainage takes fluid out, Excision cuts out a portion of a body part, and Resection removes all of one. Picking the right root operation is the central skill of PCS coding, so each one above carries its official CMS definition.
Related References
Source: CMS FY 2027 ICD-10-PCS order file and code tables, effective October 1, 2026 through September 30, 2027.
