C1 Esterase Inhibitor (C1-INH) Test

The C1 Esterase Inhibitor (C1-INH) test measures the level or function of C1 esterase inhibitor, a protein that regulates the complement system and prevents excessive inflammation. This test is mainly used to diagnose Hereditary Angioedema (HAE) and Acquired Angioedema (AAE), conditions that cause episodes of severe swelling.

Why is the C1 Esterase Inhibitor Test Done?

✅ To Diagnose Hereditary Angioedema (HAE)

• A rare genetic disorder that causes recurrent swelling in the face, lips, throat, hands, feet, and abdomen.

✅ To Diagnose Acquired Angioedema (AAE)

• A condition similar to HAE but develops later in life, often due to autoimmune diseases or cancers.

✅ To Investigate Recurrent Swelling or Abdominal Pain

• If no clear allergic cause is found, this test helps rule out HAE/AAE.

✅ To Monitor C1-INH Levels in Patients with Angioedema

• Ensures appropriate treatment and management.

Types of C1 Esterase Inhibitor Tests

1️⃣ C1 Esterase Inhibitor Antigen Test (C1-INH Level Test)

• Measures the amount of C1-INH protein in the blood.
• Low levels indicate HAE Type 1 (85% of cases).

2️⃣ C1 Esterase Inhibitor Functional Test (C1-INH Activity Test)

• Measures how well C1-INH is functioning.
• Normal levels but low activity indicate HAE Type 2.

3️⃣ C4 Complement Test

• C4 is usually low in HAE and AAE.
• Often ordered along with C1-INH tests.

Test Procedure

🩸 Sample Type:

• Blood Sample (Venous Draw)

⏳ Turnaround Time:

• 3–7 days

🔬 Method Used:

• Immunoturbidimetry or Functional Assay

C1 Esterase Inhibitor Test Results & Interpretation

📌 If C1-INH level and function are both low → HAE Type 1.
📌 If C1-INH level is normal but function is low → HAE Type 2.

What If C1 Esterase Inhibitor is Low?

🚨 If C1-INH is low, your doctor may recommend:
✅ C4 Complement Test (to confirm HAE/AAE).
✅ Genetic Testing (for HAE Type 1 & 2).
✅ C1q Test (to differentiate HAE from AAE).

Treatment Options

🔹 For Acute Attacks:

• C1-INH Replacement Therapy (Berinert, Cinryze, Ruconest)
• Bradykinin Inhibitors (Icatibant)
• Kallikrein Inhibitors (Ecallantide)

🔹 For Long-Term Prevention:

• C1-INH Concentrates
• Androgens (Danazol, Stanozolol)
• Antifibrinolytics (Tranexamic Acid)

🚨 Angioedema affecting the airway is a medical emergency! Seek immediate medical attention if swelling occurs in the throat or breathing is difficult.

Key Takeaways

🔹 C1-INH testing is crucial for diagnosing Hereditary & Acquired Angioedema.
🔹 Low C1-INH levels = HAE Type 1; Low function but normal levels = HAE Type 2.
🔹 C4 levels are also typically low in HAE & AAE.
🔹 Treatment focuses on managing acute attacks and long-term prevention.
🔹 If experiencing recurrent unexplained swelling, C1-INH testing is recommended.