ICD-10 Code B27.1 – Cytomegaloviral Mononucleosis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code B27.1 – Cytomegaloviral mononucleosis
What it is
B27.1 identifies mononucleosis caused by cytomegalovirus (CMV). Use it when the record documents CMV as the cause of the mono-like illness, rather than Epstein-Barr virus.
Clinical signs
Typical findings include fever, fatigue, sore throat, and enlarged lymph nodes. Clinical features vary; refer to documentation, especially when the note distinguishes CMV infection from other causes of mononucleosis.
When to use this code
Use B27.1 when the clinician documents cytomegaloviral mononucleosis, CMV mononucleosis, or a mono-like syndrome attributed to CMV. Code it from the documented diagnosis, not from a positive CMV test alone. If the record is unclear about the cause, check documentation before assigning this code.
Do not use for
Do not use B27.1 for infectious mononucleosis due to Epstein-Barr virus or for unspecified mononucleosis. Also avoid it when CMV is documented without mononucleosis; use the code that matches the stated condition.
Coding tip
Confirm that CMV is named as the cause in the assessment or discharge diagnosis before you assign B27.1.