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Research C1 Esterase Inhibitor, Serum
Immune System

C1 Esterase Inhibitor, Serum

Optimal Result: 21 - 39 mg/dL.

Measurement of the C1 esterase inhibitor (the first component of the complement) is used to diagnose hereditary angioedema and to monitor levels of the inhibitor during treatment.

What is hereditary angioedema?

Hereditary angioedema is a disorder characterized by recurrent episodes of severe swelling (= angioedema). The most common areas of the body to develop swelling are the limbs, face, intestinal tract, and airway. Minor trauma or stress may trigger an attack, but swelling often occurs without a known trigger. Episodes involving the intestinal tract cause severe abdominal pain, nausea, and vomiting. Swelling in the airway can restrict breathing and lead to life-threatening obstruction of the airway. About one-third of people with this condition develop a non-itchy rash called erythema marginatum during an attack.

Symptoms of hereditary angioedema typically begin in childhood and worsen during puberty. On average, untreated individuals have an attack every 1 to 2 weeks, and most episodes last for about 3 to 4 days. The frequency and duration of attacks vary greatly among people with hereditary angioedema, even among people in the same family.

There are three types of hereditary angioedema, called types I, II, and III, which can be distinguished by their underlying causes and levels of a protein called C1 inhibitor in the blood. The different types have similar signs and symptoms. Type III was originally thought to occur only in women, but families with affected males have been identified.

The most common form (85% of cases) of hereditary angioedema is due to an absolute decrease in the amount of C1 esterase inhibitor. A less common form (15% of cases) is due to the functional abnormality of the inhibitor where levels may be normal. Both abnormalities need to be tested because of the potentially life-threatening nature of the disease.

In addition to the decreased serum esterase C1 inhibitor in patients with hereditary angioedema, there is still a unique quinine polypeptide at elevated concentration during the edema crisis. Patients with episodes of hereditary angioedema also have a low total complement and C4 and C2 components of the complement. Hereditary angioedema is transmitted in an autosomal dominant manner. Heterozygotes also have reduced levels of the C1 esterase inhibitor. During acute attacks of the disease, complement components of C4 and C2 may be significantly reduced, but C1 and C3 components are normal. The factors that promote the onset of angioedema attacks are often unknown.

Notes:

- Angioedema can also occur as an acquired disease. The acquired form includes non-hereditary C1 esterase deficiency and may be caused by medications, allergies, idiopathic forms, angioedema associated with autoimmune disease especially with systemic lupus erythematosus and hypereosinophilia, angioedema occasionally associated with malignancy, and angioedema caused by natural stimuli.

- Abnormally low results are consistent with a heterozygous C1 esterase inhibitor deficiency and hereditary angioedema.

- Fifteen percent of hereditary angioedema patients have a normal or elevated level but nonfunctional C1 esterase inhibitor protein. Detection of these patients requires a functional measurement of C1 esterase inhibitor; FC1EQ / C1 Esterase Inhibitor, Functional Assay, Serum.

- Measurement of C1q antigen levels; C1Q / Complement C1q, Serum, is key to the differential diagnoses of acquired or hereditary angioedema. Those patients with the hereditary form of the disease will have normal levels of C1q, while those with the acquired form of the disease will have low levels.

- Studies in children show that adult levels of C1 inhibitor are reached by 6 months of age.

References:

Atkinson JP, Du Clos TW, Mold C, Kulkarni H, Hourcade D, Wu X. The human complement system: basic concepts and clinical relevance. In: Rich RR, Fleisher TA, Shearer WT, Schroeder HW, Frew AJ, Weyand CM, eds. Clinical Immunology: Principles and Practice. 5th ed. Philadelphia, PA: Elsevier; 2019:chap 21.

Cicardi M, Aberer W, Banerji A, et al. Classification, diagnosis, and approach to treatment for angioedema: consensus report from the Hereditary Angioedema International Working Group. Allergy. 2014;69(5):602-616. PMID: 24673465 www.ncbi.nlm.nih.gov/pubmed/24673465/.

Leslie TA, Greaves MW. Hereditary angioedema. In: Lebwohl MG, Heymann WR, Berth-Jones J, Coulson IH, eds. Treatment of Skin Disease: Comprehensive Therapeutic Strategies. 5th ed. Philadelphia, PA: Elsevier; 2018:chap 101.

Zanichelli A, Azin GM, Wu MA, et al. Diagnosis, course, and management of angioedema in patients with acquired C1-inhibitor deficiency. J Allergy Clin Immunol Pract. 2017;5(5):1307-1313. PMID: 28284781 www.ncbi.nlm.nih.gov/pubmed/28284781/.

Frank MM: Complement deficiencies. Pediatr Clin North Am. 2000;47(6):1339-1354

Gelfand JA, Boss GR, Conley CL, et al: Acquired C1 esterase inhibitor deficiency and angioedema: a review. Medicine. 1979;58(4):321-328

Rosen FS, Alper CA, Pensky J, et al: Genetically determined heterogeneity of the C1 esterase inhibitor in patients with hereditary angioneurotic edema. J Clin Invest. 1971;50(10):2143-2149

Frigas E: Angioedema with acquired deficiency of the C1 inhibitor: a constellation of syndromes. Mayo Clin Proc. 1989;64:1269-1275

Soldin SJ, Hicks JM, Bailey J, et al: Pediatric reference ranges for estradiol and C1 esterase inhibitor. Clin Chem. 1998;44(6s):A17

What does it mean if your C1 Esterase Inhibitor, Serum result is too high?

C1 esterase inhibitor (C1-INH) is a protein found in the fluid part of your blood. It controls a protein called C1, which is part of the complement system.

The complement system is a group of nearly 60 proteins in blood plasma or on the surface of some cells. The complement proteins work with your immune system to protect the body from infections. They also help remove dead cells and foreign material. There are nine major complement proteins. They are labeled C1 through C9. Rarely, people may inherit deficiency of some complement proteins. These people are prone to certain infections or autoimmune disorders.

What does it mean if your C1 Esterase Inhibitor, Serum result is too low?

Low levels of C1-INH may cause certain types of angioedema. Angioedema results in sudden swelling of the tissues of the face, upper throat and tongue. It may also cause difficulty breathing. Swelling in the intestine and abdominal pain may also occur. There are two types of angioedema that result from decreased levels of C1-INH. Hereditary angioedema affects children and young adults under age 20. Acquired angioedema is seen in adults older than age 40. Adults with acquired angioedema are much more likely to also have other conditions, such as such as cancer or autoimmune disease.

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