ICD-10 Code A42.0 – Pulmonary actinomycosis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code A42.0 – Pulmonary actinomycosis
What it is
Pulmonary actinomycosis is a chronic bacterial infection of the lungs caused by Actinomyces species. It often develops slowly and may involve lung tissue, the pleura, or nearby chest structures.
Clinical signs
Clinical features vary; refer to documentation. Common findings include chronic cough, chest pain, fever, weight loss, and imaging abnormalities that can resemble pneumonia or a lung mass.
When to use this code
Use A42.0 when the record specifically documents pulmonary actinomycosis or actinomycotic infection of the lung. Code it when the provider identifies the lung as the primary site, even if symptoms are nonspecific.
Assign this code based on confirmed clinical documentation, pathology, or specialist assessment. If the note only says suspected infection or an unspecified pulmonary abscess, check documentation before coding.
Do not use for
Do not use A42.0 for actinomycosis limited to other sites, such as cervicofacial or abdominal disease. Do not use it for routine bacterial pneumonia or an undifferentiated lung lesion without documentation.
Coding tip
Verify the anatomic site in the final diagnosis; actinomycosis codes are site-specific, so pulmonary involvement must be clearly stated.