Lab Test

C1 Esterase Inhibitor Antigen, Serum (C1ES)

C1 Esterase Inhibitor Antigen, C1 Inhibitor Level, C1 Esterase Inhibitor Quantitative, C-1-Esterase Inhibitor Antigen (C1ES), Serum

Test Codes

EPIC: LAB5958, Beaker: XC1AG, Mayo: C1ES


Send Outs


It is preferred that the patient fasts for 12 hours prior to specimen collection, but not required.

Specimen Collection Criteria

Collect (preferred specimen): One plain Red-top tube.
Also acceptable: One Gold-top SST tube.

Physician Office/Draw Specimen Preparation

Let specimen clot 30-60 minutes then centrifuge to separate serum from cells. Transfer serum to a plastic transport tube and freeze (-20°C/-4°F or below).

Preparation for Courier Transport

Transport: 1.0 mL serum, frozen (-20°C/-4°F or below). (Minimum: 0.5 mL)

Rejection Criteria

  • Grossly lipemic specimens.
  • Grossly hemolyzed specimens.
  • Grossly icteric specimens.
  • Specimens not collected and processed as indicated.

In-Lab Processing

Let specimen clot 30-60 minutes then centrifuge to separate serum from cells. Transfer serum to a plastic transport tube and freeze (-20°C/-4°F or below).

Transport: 1.0 mL serum, frozen (-20°C/-4°F or below). (Minimum: 0.5 mL)


Specimen Stability for Testing:

Room Temperature (20-26°C or 68-78.8°F): Unacceptable
Refrigerated (2-8°C or 36-46°F): 28 days
Frozen (-20°C/-4°F or below): 28 days

Specimen Storage in Department Prior to Disposal:

Specimen retention time is determined by the policy of the reference laboratory. Contact the Send Outs Laboratory with any questions.


Sent to Mayo Medical Laboratories, Rochester, MN.


Monday – Friday.
Results available in 2-3 days.

Reference Range

By report.

Test Methodology


Caution: 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.


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 esterase inhibitor are reached by 6 months of age.

Clinical Utility

This assay aids in the diagnosis of the congenital form of angioedema (hereditary angioedema). Hereditary angioedema is characterized by transient but recurrent attacks of nonpruritic swelling of various tissues throughout the body. The gastrointestinal tract is often involved leading to recurrent episodes of cramping abdominal pain. The most frequent cause of death in this disease is airway obstruction secondary to laryngeal edema occurring during an attack.


  1. Cugno M, et al. Plasma levels of C1 inhibitor complexes and cleaved C1 inhibitor in patients with hereditary angioneurotic edema. J Clin Invest 1990; 85:1215-1220.
  2. Lachmann PJ, et al. The catabolism of C1-inhibitor and the pathogenesis of hereditary angio-edema. Acta Pathol Microbiol Immunol Scand 1984; 92(S):35-39.
  3. Marcus-Bagley D et al. Methods for allotyping complement proteins. In Manual of clinical immunology, 4th ed. NR Rose, et al, eds. 1992; Washington: Am Soc Microbiol, 124-140.
  4. Quastel M, et al. Behavior in vivo of normal and dysfunctional C1 inhibitor in normal subjects and patients with hereditary angioneurotic edema. J Clin Invest 1983; 71:1041-1046.
  5. Travis J and Salvesen GS. Human plasma proteinase inhibitors. Ann Rev Biochem 1983; 52:655.
  6. Ziccardi RJ and Cooper NR. Development of an immunochemical test to assess C1 inactivator function in human serum and its use for the diagnosis of hereditary angioedema. Clin Immunol Immunopathol 1980;15:465.

CPT Codes

LOINC:  48494-9


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