T25.421A (Corrosion of unspecified degree of right foot, initial encounter) compared with T25.421S (Corrosion of unspecified degree of right foot, sequela), from the official CMS tabular data. T25.421A and T25.421S code the same injury at a different phase of treatment.
Same underlying diagnosis, different encounter phase.
The 7th character records the phase of care for the encounter being coded, so a single encounter takes one of these characters, not several. Review whether both phases belong on the same episode of care.
Source: ICD-10-CM Official Guidelines, Section I.C.19.a
Same injury, other encounter phase. T25.421A and T25.421S code the same injury at a different phase of treatment, set by the 7th character.
The 7th character records the type of care given at the encounter being coded (ICD-10-CM Official Guidelines, Section I.C.19.a), so one encounter takes one of these, not both.
| T25.421ACorrosion of unspecified degree of right foot, initial encounter | T25.421SCorrosion of unspecified degree of right foot, sequela | |
|---|---|---|
| Billing status | Billable | Billable |
| Classification | S00-T88 — Injury, poisoning and certain other consequences of external causes | S00-T88 — Injury, poisoning and certain other consequences of external causes |
| Definition | Corrosion of unspecified degree of right foot, initial encounter is a billable ICD-10-CM diagnosis code (T25.421A). | Corrosion of unspecified degree of right foot, sequela is a billable ICD-10-CM diagnosis code (T25.421S). |
| 7th character | The appropriate 7th character is to be added to each code from category T25 | The appropriate 7th character is to be added to each code from category T25 |
| Includes | burns and corrosions of first degree [erythema] burns and corrosions of second degree [blisters][epidermal loss] burns and corrosions of third degree [deep necrosis of underlying tissue] [full- thickness skin loss] | burns and corrosions of first degree [erythema] burns and corrosions of second degree [blisters][epidermal loss] burns and corrosions of third degree [deep necrosis of underlying tissue] [full- thickness skin loss] |
| Use additional code | external cause code to identify place (Y92) code from category T31 or T32 to identify extent of body surface involved | external cause code to identify place (Y92) code from category T31 or T32 to identify extent of body surface involved |
| Code first | (T51-T65) to identify chemical and intent | (T51-T65) to identify chemical and intent |
Derived from the official CMS ICD-10-CM tabular data (FY2026). Not billing advice; verify sequencing rules for the encounter. All data sources