C1 Esterase Inhibitor

Categories Lab Test, Pathology Test Tag 5 DAYS REPORTS

C1 Esterase Inhibitor (C1-INH) – Diagnostic Test for Hereditary Angioedema (HAE)

C1 Esterase Inhibitor (C1-INH) is a protein involved in the regulation of the complement system. It plays a crucial role in controlling inflammation and preventing excessive swelling (angioedema). Deficiency or dysfunction of C1-INH is the primary cause of Hereditary Angioedema (HAE).

1. Types of C1 Esterase Inhibitor Tests

There are two key tests for C1-INH:

Test Type	Purpose	Interpretation
C1-INH Quantitative (Antigenic Level)	Measures the amount of C1-INH in blood	Low in Type 1 HAE
C1-INH Functional (Activity Level)	Measures how well C1-INH is functioning	Low in Type 2 HAE

2. Normal Reference Ranges

Test	Normal Range
C1 Esterase Inhibitor (Antigenic Level)	21 – 39 mg/dL
C1 Esterase Inhibitor (Functional Activity)	> 50% activity

🔹 Low antigenic levels = Type 1 HAE (85% of cases)
🔹 Normal antigenic levels but low functional activity = Type 2 HAE (15% of cases)

3. Clinical Significance of C1 Esterase Inhibitor Deficiency

🔻 Decreased C1-INH Levels

Condition	Explanation
Hereditary Angioedema (HAE) Type 1	Low C1-INH protein and function
Hereditary Angioedema (HAE) Type 2	Normal C1-INH levels but reduced function
Acquired Angioedema (AAE)	Associated with autoimmune diseases or B-cell lymphomas

🔺 Elevated C1-INH Levels (Rare)

Condition	Explanation
Inflammatory Conditions	Slight elevation in chronic infections, autoimmune diseases
Liver Disease	Increased production in response to liver dysfunction

4. Why is C1 Esterase Inhibitor Measured?

✅ Diagnosing Hereditary Angioedema (HAE) – Recurrent episodes of swelling (face, airway, GI tract)
✅ Distinguishing between HAE and allergic angioedema – HAE does not respond to antihistamines or steroids
✅ Evaluating Acquired Angioedema (AAE) – Associated with autoimmune diseases or cancers
✅ Assessing Complement System Disorders – Used alongside C4 and CH50 complement tests

5. Additional Tests for Hereditary Angioedema (HAE) Diagnosis

Test	Findings in HAE
C1-INH (Quantitative Level)	Low in Type 1, Normal in Type 2
C1-INH (Functional Activity)	Low in Type 1 and Type 2
C4 Complement Level	Low in both HAE Type 1 & 2
C1q Complement Level	Low in Acquired Angioedema (AAE), Normal in HAE

Key Takeaways

✅ C1-INH deficiency causes Hereditary Angioedema (HAE), leading to recurrent swelling episodes.
✅ HAE Type 1 → Low C1-INH levels; HAE Type 2 → Normal levels but low function.
✅ C4 is also low in HAE, while C1q is normal (C1q is low in acquired angioedema).
✅ C1-INH testing helps distinguish HAE from allergic angioedema, which responds to antihistamines.

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