T78.49XA (Other allergy, initial encounter) compared with T78.49XD (Other allergy, subsequent encounter), from the official CMS tabular data. T78.49XA and T78.49XD 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. T78.49XA and T78.49XD 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.
| T78.49XAOther allergy, initial encounter | T78.49XDOther allergy, subsequent encounter | |
|---|---|---|
| Billing status | Billable | Billable |
| Classification | S00-T88 — Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88) | S00-T88 — Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88) |
| Definition | Other allergy, initial encounter is a billable ICD-10-CM diagnosis code (T78.49A). | Other allergy, subsequent encounter is a billable ICD-10-CM diagnosis code (T78.49D). |
| 7th character | The appropriate 7th character is to be added to each code from category T78 | The appropriate 7th character is to be added to each code from category T78 |
Derived from the official CMS ICD-10-CM tabular data (FY2026). Not billing advice; verify sequencing rules for the encounter. All data sources