FY2027
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Excludes1 pair

A51.0 vs N77.1

A51.0 and N77.1 are not coded together. ICD-10-CM declares them mutually exclusive with an Excludes1 note — the two conditions are not expected to occur together, so exactly one of them is normally correct for a given encounter. The Official Guidelines carve out one exception: if the two conditions are clearly unrelated to each other, both may be reported.

The official note, declared on N77.1
vulvovaginitis in early 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 (primary)
  • Chancre › urethra
  • Lesion › primary
  • Syphilis, syphilitic › bubo (primary)
N77.1

Vaginitis, vulvitis and vulvovaginitis in diseases classified elsewhere

Billable
Chapter 14
Diseases of the genitourinary system
Section
N70-N77
Indexed under
  • Vaginitis › in › pinworm infection

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