J21.9Acute bronchiolitis, unspecified

J21.9 is the ICD-10-CM diagnosis code for acute bronchiolitis, unspecified. It belongs to category J21 (acute bronchiolitis), block J20-J22 (other acute lower respiratory infections) and chapter 10 (diseases of the respiratory system). It is billable, so it can be reported on its own for dates of service from October 1, 2026 through September 30, 2027.

Within J21, choose J21.9 (unspecified) only when documentation doesn't support a more specific option: due to respiratory syncytial virus (J21.0), due to human metapneumovirus (J21.1) and due to other specified organisms (J21.8).

Don't report J21.9 together with the conditions in its Excludes1 note: chronic bronchiolitis (J44.89).

As a secondary diagnosis it is a CC (complication or comorbidity), which can move an inpatient stay into the "with CC" MS-DRG of its family, unless the principal diagnosis excludes it.

In MS-DRG v44.0, it is part of the grouping logic for DRG 202 (Bronchitis and Asthma with CC/MCC, relative weight 0.9474) and DRG 203 (Bronchitis and Asthma without CC/MCC, relative weight 0.6512), in MDC 04 (Diseases and Disorders of the Respiratory System), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.

Before ICD-10, this condition was coded in ICD-9-CM as 466.19 (acute bronchiolitis due to other infectious organisms).