A09 — Infectious gastroenteritis and colitis, unspecified
A09 is a billable, specific ICD-10-CM code for infectious gastroenteritis and colitis, unspecified. It is valid for submission on a claim.
Excludes1 — never code together
These conditions cannot occur together. Billing both on the same encounter is a denial.
Inclusion terms
Alternative wordings a physician may use in the chart for this same code.
- Infectious colitis NOS
- Infectious enteritis NOS
- Infectious gastroenteritis NOS
Other codes that can never be billed with A09
These codes carry an Excludes1 note pointing at A09. The conflict binds both ways, but ICD-10-CM only writes it down on one side — so you would not find this by reading A09 alone.
- K52.9Noninfective gastroenteritis and colitis, unspecified
Risk adjustment
A09 does not map to an HCC and does not risk-adjust under CMS-HCC V28. That is normal — most ICD-10 codes do not. It still needs to be coded correctly; it just will not move a RAF score.
Medicare coverage
A09 is named in 10 Medicare coverage policies — 10 listing it as supporting medical necessity. Which of them applies to you depends on your Medicare contractor, and coverage genuinely differs by state.
- A55937Billing and Coding: Diagnostic Colonoscopy
- A56394Billing and Coding: Colonoscopy and Sigmoidoscopy-Diagnostic
- A56456Billing and Coding: Colonoscopy/Sigmoidoscopy/Proctosigmoidoscopy
- A56632Billing and Coding: Colonoscopy/Sigmoidoscopy/Proctosigmoidoscopy
How A09 is indexed
Coders do not find codes by browsing the tabular list — they look them up in the alphabetic index, under the word the physician wrote. These are the index entries that lead here, so you can see which chart wordings map to A09.
- Dysentery, dysenteric(catarrhal) (diarrhea) (epidemic) (hemorrhagic) (infectious) (sporadic) (tropical)
- Diarrhea, diarrheal›dysenteric
- Diarrhea, diarrheal›endemic
- Diarrhea, diarrheal›epidemic
- Diarrhea, diarrheal›infectious
- Disease, diseased›diarrheal, infectious NEC
- Dysentery, dysenteric›arthritis
- Enteritis›epidemic(infectious)
- Enteritis›infectious NOS
- Enteritis›septic
- Enterocolitis›infectious NEC
- Gastroenteritis›epidemic(infectious)
Questions about A09
- Is A09 a billable ICD-10-CM code?
- Yes. A09 is a billable, specific ICD-10-CM code and is valid for submission on a claim.
- Where does A09 sit in the tabular list?
- Certain infectious and parasitic diseases (A00-B99), in the block Intestinal infectious diseases (A00-A09).
- What cannot be coded together with A09?
- A09 carries an Excludes1 note, which means the conditions it lists can never be coded together with it on the same encounter.