Search our Test Catalog. Specify what to search (name, test code, titles, everywhere) and how to search (begins with, contains)

Unit Code 8198:
C1 Esterase (C1ES) Inhibitor Antigen, Serum

Print Friendly View
Print Page Email Page

Useful For

Diagnosis of hereditary angioedema

 

Monitoring levels of C1 esterase inhibitor in response to therapy

Clinical Information

C1 esterase inhibitor blocks the activation of C1 (first component

of the complement cascade) to its active form. The deficiency of

C1 esterase inhibitor results in the inappropriate activation of C1

and the subsequent release of an activation peptide from C2 with

kinin-like activity. Thiskinin-like peptide enhances vascular

permeability. C1 esterase inhibitor deficiency results in hereditary

or acquired angioedema. This disease is an autosomal dominant

inherited condition, in which exhaustion of the abnormally low levels

of C1 esterase inhibitor results in C1 activation, breakdown of C2 and

C4, and subsequent acute edema of subcutaneous tissue, the

gastrointestinal tract, or the upper respiratory tract. The disease

responds to attenuated androgens.

 

Because 15% of C1 inhibitor deficiencies have nonfunctional protein,

some patients will have abnormal functional results (#81493 "C1

Esterase Inhibitor, Functional Assay Quantitative, Serum") in the

presence of normal (or elevated) antigen levels.

Reference Values

19-37 mg/dL

Interpretation

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; #81493 "C1 Esterase Inhibitor,

Functional Assay Quantitative, Serum."

 

Measurement of C1q antigen levels; #8851 "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.

Cautions

Quantitation of specific proteins by nephelometric means may not be

possible in lipemic sera due to the extreme light scattering properties

of the specimen. Turbidity and particles in the specimen may result in

extraneous light scattering signals, resulting  in variable specimen analysis.

Clinical Reference

1.   Frank MM: Complement deficiencies. Pediatr Clin North Am 2000;

      47(6):1339-1354

 

2.   Gelfand JA, Boss GR, Conley CL, et al: Acquired C1

      esterase inhibitor deficiency and angioedema: a review. Medicine

      1979;58(4):321-328

 

3.   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

 

4.   Frigas E: Angioedema with acquired deficiency of the C1 inhibitor:

      a constellation of syndromes. Mayo Clin Proc 1989;64:1269-1275

 

5.   Soldin SJ, Hicks JM, Bailey J, et al: Pediatric reference

      ranges for estradiol and C1 esterase inhibitor. Clin Chem 1998;

      44(6s):A17

Key