ICD-10 Code A42 – Actinomycosis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code A42 – Actinomycosis
What it is
A42 identifies actinomycosis, a chronic bacterial infection caused by Actinomyces species. It often produces slowly progressive, localized disease with abscesses and draining sinuses.
Clinical signs
Clinical features vary; refer to documentation. Typical findings include firm swelling, pain, abscess formation, and sinus tracts that may drain thick material. Infection can involve the cervicofacial, thoracic, abdominal, or pelvic region.
When to use this code
Use A42 when the provider documents actinomycosis or actinomycotic infection. Code it when the diagnosis is confirmed and the record supports the site or extent of disease. If the documentation is vague, check documentation for the exact organism and location.
Do not use for
Do not use A42 for nonspecific abscesses, cellulitis, or other bacterial infections without documented actinomycosis. If the chart does not clearly identify Actinomyces infection, choose a more accurate code.
Coding tip
Look for the anatomic site and any documented complications, because actinomycosis coding may need additional specificity.