{"id":"c1-inhibitor-antigen","name":"C1 Esterase Inhibitor, antigenic (protein level)","shortName":"C1-INH (protein)","aliases":["C1 Esterase Inhibitor, Protein","C1 Inhibitor, Quantitative","C1-INH, Antigenic","C1 Esterase Inhibitor, Quantitative","C1 Esterase Inhibitor, Antigenic","C1-INH Antigen","C1 Inhibitor Protein","C1 INH Antigenic","C1 Esterase Inhibitor Antigen","C1 Inhibitor, Antigenic","C1 Esterase Inhibitor Antigen, S","C1 Esterase Inhibitor, Total"],"abbreviations":["C1-INH Ag","C1INH Ag","C1INHq"],"loinc":[{"code":"4477-6","primary":true}],"specimen":"serum","units":[{"ucum":"mg/dL","display":"mg/dL"},{"ucum":"g/L","display":"g/L"},{"ucum":"mg/L","display":"mg/L"},{"ucum":"ug/mL","display":"µg/mL"}],"referenceRanges":[{"population":"Adults","low":21,"high":39,"unit":"mg/dL","unitDisplay":"mg/dL","note":"Commonly printed interval for nephelometry: Quest test 298 as listed by Parkview Health Laboratory, and two published hospital reports (21 to 39 mg/dL is the same as 0.21 to 0.39 g/L). Other labs differ a little: Mayo Clinic Laboratories (nephelometry) prints 19 to 37 mg/dL and UW Medicine prints 20 to 40 mg/dL. One radial immunodiffusion kit used 19.5 to 34.5 mg/dL in a published study. Use the range on your own report. The WAO/EAACI guideline describes the protein level in hereditary angioedema type 1 as below 50% of the normal mean. These labs do not split the interval by age, but newborn levels run lower (cord blood is about 70% of adult values) and reliable reference values for children are lacking.","sources":[{"title":"C1 Esterase Inhibitor Protein (Quest send-out test 298)","url":"https://lab.parkview.com/test-directory/c1-esterase-inhibitor-protein/","publisher":"Parkview Health Laboratory"},{"title":"Hereditary Angioedema With Normal C1 Esterase Inhibitor: A Case of a Late Diagnosis in a 48-Year-Old Male","url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC12579791/","publisher":"Cureus","year":2025},{"title":"Diagnostic delay, SERPING1 allelic heterogeneity, and real-world lanadelumab prophylaxis in Chinese patients with hereditary angioedema due to C1 inhibitor deficiency","url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC13485567/","publisher":"Frontiers in Allergy","year":2026},{"title":"C1 Esterase Inhibitor Antigen, Serum (test ID C1ES)","url":"https://mml.testcatalog.org/show/C1ES","publisher":"Mayo Clinic Laboratories (Extended Catalog)"},{"title":"C1 Esterase Inhibitor Panel (lab code C1EP)","url":"https://testguide.labmed.uw.edu/view/C1EP?tabs=yes","publisher":"UW Medicine Laboratory Medicine and Pathology"},{"title":"Evaluating functional C1INH with multiple laboratory methods across Hereditary Angioedema types","url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC12417112/","publisher":"Frontiers in Immunology","year":2025},{"title":"The international WAO/EAACI guideline for the management of hereditary angioedema - The 2021 revision and update","url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC9023902/","publisher":"World Allergy Organization Journal","year":2022}]}],"review":{"status":"ai-verified","label":"AI-verified against cited sources. Awaiting expert review","lastReviewed":"2026-10-03"},"summary":"The amount of C1 inhibitor protein in your blood. A low level is one clue in the testing for hereditary angioedema.","url":"https://bloodtesttracker.com/markers/c1-inhibitor-antigen","notice":"Information, not medical advice. Ranges differ between labs, so the range on your own report is the one your result is judged against."}