L23 (Allergic contact dermatitis) compared with T78.40XA (Allergy, unspecified, initial encounter), from the official CMS tabular data. Do not report these codes together: the official tabular list marks them Excludes1.
Not coded here — these two are mutually exclusive.
“allergy NOS (T78.40)”
An Excludes1 note means the two conditions cannot occur together, so the pair should not be reported for the same encounter. The sole exception is when the conditions are documented as unrelated to each other.
Source: CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a
No — do not report together. L23 carries an Excludes1 note covering T78.40XA: “allergy NOS (T78.40)”
Sole exception: when the two conditions are documented as unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).
| L23Allergic contact dermatitis | T78.40XAAllergy, unspecified, initial encounter | |
|---|---|---|
| Billing status | Non-billable header | Billable |
| Classification | L00-L99 — Diseases of the Skin and Subcutaneous Tissue (L00-L99) | S00-T88 — Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88) |
| Definition | Allergic contact dermatitis is a non-billable ICD-10-CM category code (L23). | Allergy, unspecified, initial encounter is a billable ICD-10-CM diagnosis code (T78.40A). |
| 7th character | — | The appropriate 7th character is to be added to each code from category T78 |
| Includes | — | Allergic reaction NOS Hypersensitivity NOS |
Derived from the official CMS ICD-10-CM tabular data (FY2026). Not billing advice; verify sequencing rules for the encounter. All data sources