ICD-10 Code B27.89 – Other infectious mononucleosis with other complication (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code B27.89 – Other infectious mononucleosis with other complication
What it is
This code identifies infectious mononucleosis with a complication not captured by a more specific code. Use it for documented mononucleosis cases that include an additional clinical problem, but not one of the named complication categories.
Clinical signs
Clinical features vary; refer to documentation. Typical mononucleosis findings may include fever, pharyngitis, lymphadenopathy, fatigue, and splenomegaly, with an additional complication noted in the record.
When to use this code
Use B27.89 when the provider documents infectious mononucleosis and specifies another complication, but the chart does not support a more exact mononucleosis code. You should code from the documented complication, not from symptoms alone. Check documentation if the complication is unclear.
Do not use for
Do not use this code for uncomplicated infectious mononucleosis or when the record names a different, more specific mononucleosis subtype. Also avoid it if the complication is not documented.
Coding tip
Query the provider when mononucleosis is documented with a complication but the type of complication is not specific enough for accurate code selection.