J21 ICD-10-CM Code: Acute bronchiolitis

J21 is the ICD-10-CM diagnosis code for acute bronchiolitis. J21 sits in the ICD-10-CM chapter for diseases of the respiratory system (j00-j99), within the section covering other acute lower respiratory infections (j20-j22).

Header codes like J21 cannot be reported on claims directly, they organize child codes that share clinical context but the actual diagnosis must be coded to the highest level of specificity supported by the documentation. Coders should look at J21's child codes and select the one that matches the patient's documented presentation, since payers reject header codes submitted as the primary diagnosis. For risk adjustment workflows, header codes never contribute to a Medicare Advantage member's RAF score on their own; only billable child codes that happen to map to a payment HCC affect risk-adjusted plan payments.