ICD-11 Codes
for 4A00.1 - Defects in the complement system

Teodor Jurukovski January 1, 1970

Fact checked by: Teodor Jurukovski

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Understanding Defects in the Complement System (ICD-11 Code 4A00.1)

Defects in the complement system, identified by the ICD-11 code 4A00.1, represent a group of inherited disorders that impair the function of the complement system, a critical part of the innate immune system. This system comprises a cascade of proteins that help the body fight infections and clear cellular debris. When these components are deficient or dysfunctional, individuals become more susceptible to various health issues, particularly infections and autoimmune conditions.

Causes and Risk Factors for Complement System Defects

The primary cause of defects in the complement system is genetic. Most complement deficiencies are inherited in an autosomal recessive pattern, meaning an individual must inherit a faulty gene from both parents to be affected. However, some conditions, such as C1 inhibitor deficiency, follow an autosomal dominant inheritance pattern. These genetic mutations can lead to a lack of specific complement proteins, including early components like C1q, C1r, C1s, C2, C4, or later components such as C3, factor D, factor H, factor I, properdin, mannan-binding lectin (MBL), or mannose-binding lectin serine protease 2 (MASP-2). In some instances, these defects can also be acquired rather than inherited.

Common Symptoms and Presentation

Individuals with defects in the complement system often experience recurrent infections. A hallmark symptom is an increased susceptibility to infections caused by Neisseria bacteria, such as Neisseria meningitidis and Neisseria gonorrhoeae. Other common presentations include:

• Recurrent bacterial infections
• Frequent upper and lower respiratory tract infections
• Meningitis
• Sepsis
• Angioedema, particularly in cases of C1 inhibitor deficiency
• Increased risk of developing autoimmune diseases like lupus erythematosus

Diagnosis of Complement System Defects

Diagnosing defects in the complement system typically involves a combination of clinical evaluation and laboratory testing. Healthcare providers will assess the patient's history of infections and family history of similar conditions. Key diagnostic tests include:

• Complement component assays: These blood tests measure the levels and functional activity of specific complement proteins (e.g., CH50, AH50, C3, C4, C1q levels).
• Genetic testing: Molecular genetic analysis can identify specific gene mutations responsible for the complement deficiency.

The ICD-11 code for this condition is 4A00.1.

Treatment and Management Considerations

Management strategies for defects in the complement system aim to prevent infections, treat active infections promptly, and manage associated complications. Treatment approaches may include:

• Prophylactic antibiotics: Long-term use of antibiotics, particularly penicillin, is often prescribed to prevent Neisseria infections.
• C1 inhibitor concentrate: For patients with hereditary angioedema due to C1 inhibitor deficiency, replacement therapy with C1 inhibitor concentrate can be used for acute attacks and long-term prophylaxis.
• Plasma infusions: In some cases, fresh frozen plasma may be administered to provide missing complement components.
• Management of autoimmune conditions: If autoimmune diseases develop, they are treated according to standard protocols.

Patients experiencing recurrent infections or a family history of immune deficiencies should seek medical advice for appropriate evaluation and diagnosis.

Documentation and Coding for Defects in the Complement System

Accurate documentation and coding are essential for patient care and billing. The official ICD-11 code for defects in the complement system is 4A00.1. This code is used to report conditions related to deficiencies in the complement pathway. Common clinical synonyms and related terms that may be documented include immunodeficiency due to complement component deficiency, hereditary angioedema (when related to C1 inhibitor deficiency), and recurrent Neisseria infections due to complement defects. When coding, healthcare professionals should ensure the documentation clearly specifies the nature of the complement defect, whether it involves early or late components, or specific proteins, to ensure precise reporting for billing and statistical purposes.