ICD-10 Code B27.0 – Gammaherpesviral mononucleosis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code B27.0 – Gammaherpesviral mononucleosis
What it is
B27.0 identifies mononucleosis caused by gammaherpesviruses, most commonly Epstein-Barr virus. Use it for documented gammaherpesviral infectious mononucleosis, not for nonspecific viral illness.
Clinical signs
Typical findings include fever, sore throat, swollen lymph nodes, and fatigue. Clinical features vary; refer to documentation for the confirmed viral cause and supporting exam findings.
When to use this code
Use B27.0 when the provider documents gammaherpesviral mononucleosis or Epstein-Barr virus mononucleosis. It fits encounters where the diagnosis is established, even if the note focuses on supportive care or follow-up.
If the record only says “mono” or “viral syndrome,” check documentation before assigning this code. Code the confirmed condition rather than a suspected or unspecified infection.
Do not use for
Do not use B27.0 for mononucleosis from another cause, such as cytomegalovirus, or for unspecified infectious mononucleosis. Check documentation if the viral agent is not clearly identified.
Coding tip
Assign B27.0 only when the chart links mononucleosis to a gammaherpesvirus, especially Epstein-Barr virus, or the provider states that diagnosis explicitly.