A09 — Infectious gastroenteritis and colitis, unspecified
Is A09 billable?
Yes, but A09 is an unspecified code. A09 is a valid, billable ICD-10-CM code for encounters from October 1, 2026 through September 30, 2027. However, A09 is an unspecified or catch-all code. Payers apply additional scrutiny to unspecified codes and many deny them when the medical record supports a more specific option, so check the documentation before selecting A09.
A09 at a glance
| Code | A09 |
|---|---|
| Description | Infectious gastroenteritis and colitis, unspecified |
| Billable | Yes |
| Code set | ICD-10-CM FY2027 |
| Valid for encounters | October 1, 2026 – September 30, 2027 |
Which MS-DRGs does A09 group to?
A09 sits in MDC 06 and helps define the logic of 2 MS-DRGs (version 44, FY2027). Which one a stay actually groups to also depends on procedures and secondary diagnoses.
- 391Esophagitis, Gastroenteritis and Miscellaneous Digestive Disorders with MCCmedical
- 392Esophagitis, Gastroenteritis and Miscellaneous Digestive Disorders without MCCmedical
As a secondary diagnosis, A09 is a complication or comorbidity (CC), which can move a stay into a higher-paying DRG.
How is A09 listed in the Alphabetic Index?
These are the routes through the Alphabetic Index that lead to A09. They show the wording a clinician may have documented, which often differs from the Tabular description.
- Dysentery, dysenteric (catarrhal) (diarrhea) (epidemic) (hemorrhagic) (infectious) (sporadic) (tropical)
- Diarrhea, diarrheal › dysenteric (disease) (infantile) (inflammatory)
- Diarrhea, diarrheal › endemic (disease) (infantile) (inflammatory)
- Diarrhea, diarrheal › epidemic (disease) (infantile) (inflammatory)
- Diarrhea, diarrheal › infectious (disease) (infantile) (inflammatory)
- Disease, diseased › diarrheal, infectious NEC
- Dysentery, dysenteric › arthritis (catarrhal) (diarrhea) (epidemic) (hemorrhagic) (infectious) (sporadic) (tropical)
- Enteritis › epidemic (acute) (diarrheal) (hemorrhagic) (noninfective)
- Enteritis › infectious NOS (acute) (diarrheal) (hemorrhagic) (noninfective)
- Enteritis › septic (acute) (diarrheal) (hemorrhagic) (noninfective)
- Enterocolitis › infectious NEC
- Gastroenteritis › epidemic (acute) (chronic) (noninfectious)
Excludes1 — never code together
The conditions below can never be reported together with A09 on the same claim. An Excludes1 note means the two conditions cannot occur in the same patient, so reporting both is a coding error.
Inclusion terms
Alternative wording in documentation that is classified to A09.
- Infectious colitis NOS
- Infectious enteritis NOS
- Infectious gastroenteritis NOS
Use additional code — inherited from Chapter 1
Report an additional code alongside A09 to fully describe the condition. A09 is sequenced first.
- code to identify resistance to antimicrobial drugs (Z16.-)
Excludes2 — not included here — inherited from Chapter 1
The conditions below are not part of A09, but a patient may have both at the same time. When documentation supports it, A09 and the excluded code may both be reported.
- carrier or suspected carrier of infectious disease (Z22.-)
- certain localized infections - see body system-related chapters
- infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)
- infectious and parasitic diseases specific to the perinatal period (P35-P39)
- influenza and other acute respiratory infections (J00-J22)
How long has A09 existed?
A09 has been in ICD-10-CM since at least FY2016, the earliest fiscal year on record here.
Derived from the official order files for FY2016–FY2026. FY2017 and FY2020 publish no order file, so those years are not covered.
Which codes are confused with A09?
ICD-10-CM declares these codes mutually exclusive with A09 — exactly one of each pair can be correct for a given encounter.