{"id":"c1-inhibitor-function","name":"C1 Esterase Inhibitor, functional","shortName":"C1-INH (function)","aliases":["C1 INH Functional","C1-INH Activity","C1 Esterase Inhibitor Function","C1 Inhibitor, Functional","C1 Esterase Inhibitor, Functional, Serum","C1 Esterase Inhib, Functional, S","Functional C1-INH","C1 Esterase Inhibitor Functional Activity","C1-INH Functional Assay","C1 Inhibitor Activity","C1 Esterase Inhibitor Activity","C1 Esterase Inhibitor, Functional (Chromogenic)","C1 Inhibitor Function","C1 Esterase Inh, Functional"],"abbreviations":["C1-INH Fx","fC1-INH","C1INH Function"],"loinc":[{"code":"48494-9","primary":true},{"code":"4476-8","primary":false},{"code":"82876-4","primary":false}],"specimen":"serum","units":[{"ucum":"%","display":"% of normal"}],"referenceRanges":[{"population":"Adults","low":67,"high":null,"unit":"%","unitDisplay":"% of normal","note":"Mayo Clinic Laboratories calls results above 67% of normal \"normal\" (41 to 67% equivocal, below 41% abnormal), so a result of exactly 67% is equivocal there. UW Medicine calls above 68% normal (41 to 68% equivocal). Two published hospital reports print 67% or 68% as the lower limit. The scale is a percent of normal, and the labs checked print only a lower limit, so there is no upper limit to compare against. Results are not interchangeable between assay methods. Use the cutoff printed on your own report.","sources":[{"title":"C1 Esterase Inhibitor, Functional, Serum (test ID C1INF)","url":"https://testcatalog.org/show/C1INF","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":"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}]}],"review":{"status":"ai-verified","label":"AI-verified against cited sources. Awaiting expert review","lastReviewed":"2026-10-03"},"summary":"How well your C1 inhibitor protein works, shown as a percent of normal. A low result is a key clue in testing for hereditary angioedema.","url":"https://bloodtesttracker.com/markers/c1-inhibitor-function","notice":"Information, not medical advice. Ranges differ between labs, so the range on your own report is the one your result is judged against."}