S00.421A (Blister (nonthermal) of right ear, initial encounter) compared with S00.421S (Blister (nonthermal) of right ear, sequela), from the official CMS tabular data. S00.421A and S00.421S code the same injury at a different phase of treatment. MedCoder-derived
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. S00.421A and S00.421S 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.
| S00.421ABlister (nonthermal) of right ear, initial encounter | S00.421SBlister (nonthermal) of right ear, 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 | Blister (nonthermal) of right ear, initial encounter is a billable ICD-10-CM diagnosis code (S00.421A). | Blister (nonthermal) of right ear, sequela is a billable ICD-10-CM diagnosis code (S00.421S). |
| 7th character | The appropriate 7th character is to be added to each code from category S00 | The appropriate 7th character is to be added to each code from category S00 |
| Includes | injuries of ear injuries of eye injuries of face [any part] injuries of gum | injuries of ear injuries of eye injuries of face [any part] injuries of gum |
Derived from the official CMS ICD-10-CM tabular data (FY2026). Not billing advice; verify sequencing rules for the encounter. All data sources