ICD-10 Code B27.09 – Gammaherpesviral mononucleosis with other complications (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code B27.09 – Gammaherpesviral mononucleosis with other complications
What it is
B27.09 identifies mononucleosis caused by a gammaherpesvirus, with complications beyond the uncomplicated illness. Use it when the record specifically documents this diagnosis and an associated complication.
Clinical signs
Clinical features vary; refer to documentation. Typical mononucleosis findings may include fever, sore throat, fatigue, lymphadenopathy, and splenomegaly, but this code also requires a documented complication.
When to use this code
Use this code when the provider documents gammaherpesviral mononucleosis and notes an additional complication, such as a complication of the infection or a related organ involvement. Code it only when the complication is clearly linked in the record. Check documentation if the chart does not specify the virus type or the complication.
Do not use for
Do not use this code for uncomplicated mononucleosis or for mononucleosis due to another organism. If the complication is not documented, choose the unspecified or more appropriate code instead.
Coding tip
Verify both the gammaherpesviral cause and the specific complication in the provider note before assigning B27.09.