D89.4 vs Q82.2
D89.4 and Q82.2 can never be reported together. ICD-10-CM declares them mutually exclusive with an Excludes1 note, meaning the two conditions cannot occur in the same patient — so exactly one of them is correct for any given encounter.
The official note, declared on D89.4
congenital cutaneous mastocytosis (Q82.2)
D89.4
Mast cell activation syndrome and related disorders
Not billable
- Chapter 3
- Diseases of the blood and blood-forming organs and certain disorders involving the immune mechanism
- Section
- D80-D89
Q82.2
Congenital cutaneous mastocytosis
Billable
- Chapter 17
- Congenital malformations, deformations, chromosomal abnormalities, and genetic disorders
- Section
- Q80-Q89
Use when the record says
- Congenital diffuse cutaneous mastocytosis
- Congenital maculopapular cutaneous mastocytosis
- Congenital urticaria pigmentosa
Indexed under
- Mastocytosis › cutaneous › congenital
- Mastocytosis › cutaneous › of neonatal onset
- Mastocytosis › cutaneous › of newborn onset
- Urticaria › pigmentosa › congenital
- Urticaria › pigmentosa › of neonatal onset
These two codes sit in different chapters of the Tabular List, which is usually the clearest signal that they describe different underlying processes rather than different degrees of the same one.
Excludes1 is not always absolute: where two conditions covered by the note are genuinely unrelated, CMS guidance permits reporting both. Document the reasoning rather than assuming it. More on Excludes1 vs Excludes2 · FY2027