ICD-10 Code B27.90 – Infectious mononucleosis, unspecified without complication (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code B27.90 – Infectious mononucleosis, unspecified without complication
What it is
B27.90 identifies infectious mononucleosis when the provider does not specify the causative agent and no complication is documented. Use it for the uncomplicated form of this viral syndrome.
Clinical signs
Typical findings include fever, sore throat, fatigue, and swollen lymph nodes, often with enlarged tonsils or spleen. Clinical features vary; refer to documentation.
When to use this code
Use B27.90 when the record states infectious mononucleosis, mononucleosis, or mono without naming the virus and without documenting complications. It also fits cases described as uncomplicated or not otherwise specified. If the note identifies a specific organism or complication, code that instead.
Do not use for
Do not use this code if the chart documents a specific cause, such as cytomegaloviral mononucleosis, or if complications are present. Check documentation for alternative codes.
Coding tip
Confirm both “unspecified” and “without complication” in the provider note before assigning B27.90.