ICD-10 Code B27.00 – Gammaherpesviral mononucleosis without complication (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code B27.00 – Gammaherpesviral mononucleosis without complication
What it is
B27.00 identifies mononucleosis caused by a gammaherpesvirus, most commonly Epstein-Barr virus, without documented complications. Use it when the record supports uncomplicated infectious mononucleosis.
Clinical signs
Typical findings include fever, sore throat, fatigue, and lymphadenopathy. Clinical features vary; refer to documentation, especially when the chart confirms mononucleosis but does not describe complications.
When to use this code
Use B27.00 when the clinician documents gammaherpesviral or Epstein-Barr–related mononucleosis and there is no mention of rupture, hepatitis, or other complication. It also fits uncomplicated cases evaluated for classic mononucleosis symptoms.
If the note only says “mono” without a viral cause, check documentation before assigning this code. Make sure the encounter is for the infection itself, not for a residual symptom or unrelated condition.
Do not use for
Do not use this code for mononucleosis with documented complications or for non-gammaherpesviral causes. Check documentation when the diagnosis is uncertain or when the provider describes a different infectious process.
Coding tip
Confirm the organism and the absence of complications in the assessment before coding B27.00.