Defects in the complement system

This code represents a group of rare genetic or acquired disorders characterized by deficiencies or abnormalities in one or more components of the complement system. These defects impair the body's immune response, leading to increased susceptibility to infections, autoimmune diseases, or inflammatory conditions.

Use this code when documentation clearly indicates a diagnosed defect in the complement system, such as C1, C2, C3, C4, C5-C9 deficiencies, or properdin/factor D/H/I deficiencies. This diagnosis is typically supported by laboratory findings demonstrating low complement levels or functional assays.

• Specify the exact complement component defect when known, if a more specific code exists (e.g., hereditary angioedema due to C1 esterase inhibitor deficiency has a more specific code).
• Always review lab results and physician notes confirming the specific complement defect.
• Consider sequencing this code as a primary diagnosis if it is the reason for the encounter, or as a secondary diagnosis if it is a co-morbidity impacting patient care.