A31.9 — Mycobacterial infection, unspecified
Is A31.9 billable?
Yes, but A31.9 is an unspecified code. A31.9 is a valid, billable ICD-10-CM code for encounters from October 1, 2026 through September 30, 2027. However, A31.9 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 A31.9 — the more specific alternatives are listed below.
A31.9 at a glance
| Code | A31.9 |
|---|---|
| Description | Mycobacterial infection, unspecified |
| Billable | Yes |
| Code set | ICD-10-CM FY2027 |
| Valid for encounters | October 1, 2026 – September 30, 2027 |
Which MS-DRGs does A31.9 group to?
A31.9 sits in MDC 18 and helps define the logic of 3 MS-DRGs (version 44, FY2027). Which one a stay actually groups to also depends on procedures and secondary diagnoses.
- 867Other Infectious and Parasitic Diseases Diagnoses with MCCmedical
- 868Other Infectious and Parasitic Diseases Diagnoses with CCmedical
- 869Other Infectious and Parasitic Diseases Diagnoses without CC/MCCmedical
As a secondary diagnosis, A31.9 is a complication or comorbidity (CC), which can move a stay into a higher-paying DRG.
How is A31.9 listed in the Alphabetic Index?
These are the routes through the Alphabetic Index that lead to A31.9. They show the wording a clinician may have documented, which often differs from the Tabular description.
- Mycobacterium, mycobacterial (infection)
- Mycobacterium, mycobacterial › anonymous (infection)
- Mycobacterium, mycobacterial › atypical (infection)
- Disease, diseased › photochromogenic › nonpulmonary
Inclusion terms
Alternative wording in documentation that is classified to A31.9.
- Atypical mycobacterial infection NOS
- Mycobacteriosis NOS
Use additional code — inherited from Chapter 1
Report an additional code alongside A31.9 to fully describe the condition. A31.9 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 A31.9, but a patient may have both at the same time. When documentation supports it, A31.9 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)
Excludes2 — not included here — inherited from A31
The conditions below are not part of A31.9, but a patient may have both at the same time. When documentation supports it, A31.9 and the excluded code may both be reported.
How long has A31.9 existed?
A31.9 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.