ICD-10 A09
Billable / Specific CCInfectious gastroenteritis and colitis, unspecified
About ICD-10-CM A09
ICD-10-CM code A09 represents Infectious gastroenteritis and colitis, unspecified. This is a billable/specific code in the Infectious and Parasitic Diseases chapter (block A09). The 2026 edition of ICD-10-CM A09 became effective on October 1, 2025.
Coding Tips for A09
Specialist guidance from the PayerReady Medical Coding Team. Specificity warnings, HCC capture rules, sequencing notes.
A09 is designated CC for MS-DRG grouping. On inpatient claims, this code can shift the DRG to the with-CC variant when documented as a present-on-admission secondary diagnosis. Hospital CDI programs flag CC opportunities during chart review. Failure to capture this code may leave 30 to 80 percent of the inpatient stay revenue unrealized.
Inclusion Terms / Approximate Synonyms
Clinical terms and conditions classified under A09. Per CMS ICD-10-CM Tabular 2026.
- Infectious colitis NOS
- Infectious enteritis NOS
- Infectious gastroenteritis NOS
Type 1 Excludes
Pure excludes, these codes can never be coded together with A09. The conditions are mutually exclusive (e.g., congenital vs acquired forms).
- colitis NOS (K52.9)
- diarrhea NOS (R19.7)
- enteritis NOS (K52.9)
- gastroenteritis NOS (K52.9)
- noninfective gastroenteritis and colitis, unspecified (K52.9)
Inpatient DRG Impact, CC
codes Infectious gastroenteritis and colitis, unspecified. As a Complication/Comorbidity (CC), this contributes to DRG severity adjustment when documented alongside the principal diagnosis.
Medicare LCD Coverage for A09
Local Coverage Determinations (LCDs) from CMS MACs that list A09 as a covered diagnosis.
Showing top 10 of 731 total . Click a CPT for full coverage scope.
Commercial Payer Coverage
Coverage policies from major commercial payers referencing A09.
3 Cigna
5 Medicare
CPT Codes Commonly Billed with A09
Procedures frequently paired with this diagnosis based on PayerReady's Dx↔Px linkage data.
- 44408 CMS LCD: Billing and Coding: Diagnostic Colonoscopy CMS LCD
- 45379 CMS LCD: Billing and Coding: Diagnostic Colonoscopy CMS LCD
- 44406 CMS LCD: Billing and Coding: Diagnostic Colonoscopy CMS LCD
- 45390 CMS LCD: Billing and Coding: Diagnostic Colonoscopy CMS LCD
- 45392 CMS LCD: Billing and Coding: Diagnostic Colonoscopy CMS LCD
- 44394 CMS LCD: Billing and Coding: Diagnostic Colonoscopy CMS LCD
- 44402 CMS LCD: Billing and Coding: Diagnostic Colonoscopy CMS LCD
- 44390 CMS LCD: Billing and Coding: Diagnostic Colonoscopy CMS LCD
- 44405 CMS LCD: Billing and Coding: Diagnostic Colonoscopy CMS LCD
- 44388 CMS LCD: Billing and Coding: Diagnostic Colonoscopy CMS LCD
Convert A09 to ICD-9-CM
Per CMS General Equivalence Mappings (GEMs), useful for legacy data review and historical claim analysis.
| ICD-10 | ICD-9 | Mapping Flags |
|---|---|---|
| A09 | 0090 | 10000 |
Flags format (5 digits): Approximate · No Map · Combination · Scenario · Choice List. Source: CMS 2017 GEMs (final version).
Codes Adjacent To A09
Other codes in section A00-A09 (Intestinal infectious diseases).
ICD-10 A09, Billing FAQ
Is ICD-10 code A09 billable? +
Yes, A09 is a billable ICD-10-CM code that can appear as a primary or secondary diagnosis on claims.
What other names or terms map to A09? +
ICD-10 A09 includes: Infectious colitis NOS; Infectious enteritis NOS; Infectious gastroenteritis NOS.
What codes are Type 1 Excludes for A09? +
Type 1 Excludes (never code together with A09): colitis NOS (K52.9); diarrhea NOS (R19.7); enteritis NOS (K52.9)
Is A09 a CC or MCC for inpatient DRG? +
Yes, this code is designated as CC. Documenting as a secondary diagnosis on inpatient claims can shift the DRG to a higher-weighted category.
What CPT codes are commonly billed with A09? +
Procedures frequently paired with A09 include: 44408, 45379, 44406, 45390, 45392.
What ICD-9 codes does A09 map to? +
Per CMS GEMs, A09 maps to ICD-9 codes: 0090. Useful for legacy data review and historical claim analysis.
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Reviewed by the PayerReady Medical Coding Team
Verified against the CMS 2026 code set on June 1, 2026.
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