ICD-10 Code D84.1 – Defects in the complement system (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code D84.1 – Defects in the complement system
What it is
D84.1 identifies inherited or acquired problems in the complement system, a part of immune defense. Use it when documentation states a complement deficiency or defect affecting immune function.
Clinical signs
Clinical features vary; refer to documentation. Commonly reported findings include recurrent infections, especially with encapsulated organisms, or immune-related complications tied to complement pathway dysfunction.
When to use this code
Use D84.1 when the provider documents a defect, deficiency, or abnormality of complement proteins or pathways. It may apply after laboratory workup or specialist evaluation confirms a complement system disorder. Code the documented condition, not a nonspecific infection alone.
Do not use for
Do not use this code for general immunodeficiency without a documented complement defect. Check documentation if the record only mentions infection, allergy, or another immune disorder.
Coding tip
Link the code to the specific complement abnormality documented, and query the provider if the record is vague.