FY2027
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Excludes1 pair

B58- vs P37.1

B58 and P37.1 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 B58
congenital toxoplasmosis (P37.1)
B58

Toxoplasmosis

Not billable
Chapter 1
Certain infectious and parasitic diseases
Section
B50-B64
Use when the record says
  • infection due to Toxoplasma gondii
P37.1

Congenital toxoplasmosis

Billable
Chapter 16
Certain conditions originating in the perinatal period
Section
P35-P39
Use when the record says
  • Hydrocephalus due to congenital toxoplasmosis
Indexed under
  • Hydrocephalus › due to toxoplasmosis (congenital)
  • Microcephalus, microcephalic, microcephaly › due to toxoplasmosis (congenital)
  • Microphthalmos, microphthalmia › due to toxoplasmosis
  • Toxoplasma, toxoplasmosis › congenital (acute) (subacute) (chronic)
  • Toxoplasma, toxoplasmosis › maternal, manifest toxoplasmosis in infant (acute) (subacute) (chronic)

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