ICD-10 Code I48.91 – Unspecified atrial fibrillation (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code I48.91 – Unspecified atrial fibrillation
What it is
I48.91 identifies atrial fibrillation when the record confirms AF but does not specify the type. Use it for an irregular atrial rhythm documented without a more detailed classification.
Clinical signs
Common findings include an irregularly irregular pulse, palpitations, shortness of breath, fatigue, or incidental ECG evidence of atrial fibrillation. Clinical features vary; refer to documentation.
When to use this code
Use this code when the provider documents atrial fibrillation and does not state paroxysmal, persistent, chronic, or permanent AF. It also fits when the chart only says “atrial fibrillation” or “AF” without further detail. Check documentation if another arrhythmia is described.
Do not use for
Do not use I48.91 if the record specifies a different AF type, such as paroxysmal or persistent atrial fibrillation. Do not assign it for atrial flutter or for a history of AF without current diagnosis.
Coding tip
Review the assessment and ECG report together; if the type is not stated, I48.91 is usually the correct choice.