A51.0 vs N77.0
A51.0 and N77.0 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 N77.0
ulceration of vulva in syphilis (A51.0)
A51.0
Primary genital syphilis
Billable
- Chapter 1
- Certain infectious and parasitic diseases
- Section
- A50-A64
Use when the record says
- Syphilitic chancre NOS
Indexed under
- Chancre (any genital site) (hard) (hunterian) (mixed) (primary) (seronegative) (seropositive) (syphilitic)
- Bubo › syphilitic
- Chancre › urethra (any genital site) (hard) (hunterian) (mixed) (primary) (seronegative) (seropositive) (syphilitic)
- Lesion › primary (s) (nontraumatic)
- Syphilis, syphilitic › bubo (acquired)
N77.0
Ulceration of vulva in diseases classified elsewhere
Billable
- Chapter 14
- Diseases of the genitourinary system
- Section
- N70-N77
Indexed under
- Ulcer, ulcerated, ulcerating, ulceration, ulcerative › vagina › in Behçet's disease
- Ulcer, ulcerated, ulcerating, ulceration, ulcerative › vulva › in › Behçet's disease
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