FY2027
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Excludes1 pair

A39.1 vs E27.1

A39.1 and E27.1 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 E27.1
Waterhouse-Friderichsen syndrome (A39.1)
A39.1

Waterhouse-Friderichsen syndrome

Billable
Chapter 1
Certain infectious and parasitic diseases
Section
A30-A49
Use when the record says
  • Meningococcal hemorrhagic adrenalitis
  • Meningococcic adrenal syndrome
Indexed under
  • Friderichsen-Waterhouse syndrome or disease
  • Waterhouse (-Friderichsen) syndrome or disease (meningococcal)
  • Adrenalitis, adrenitis › meningococcal, hemorrhagic
  • Apoplexia, apoplexy, apoplectic › adrenal
  • Disease, diseased › Waterhouse-Friderichsen
E27.1

Primary adrenocortical insufficiency

Billable
Chapter 4
Endocrine, nutritional and metabolic diseases
Section
E20-E35
Use when the record says
  • Addison's disease
  • Autoimmune adrenalitis
Indexed under
  • Addison's › disease or syndrome (bronze)
  • Adrenalitis, adrenitis › autoimmune
  • Disease, diseased › bronze Addison's
  • Hypoadrenalism, hypoadrenia › primary
  • Hypoadrenocorticism › primary

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