Overview: C1-Inhibitor Functional TestIntroduction: The C1-Inhibitor Functional Test measures C1 esterase inhibitor function to diagnose hereditary angioedema, causing swelling or abdominal pain. Following 2023 AAAAI guidelines, it uses an immunoassay for high specificity, aiding in autoimmune screening. This test is critical for guiding diagnosis, treatment, and improving outcomes in immunology for patients with suspected hereditary angioedema.
Other Names: C1 Esterase Functional Assay, HAE Functional Test.
FDA Status: Laboratory-developed test (LDT), meeting immunology standards for diagnostic accuracy.
Historical Milestone: C1-inhibitor testing began in the 1960s with angioedema research. Functional assays emerged in the 1980s, and by the 2000s, immunoassays improved diagnostic precision.
Purpose: Diagnoses hereditary angioedema, guides treatment, and monitors C1-inhibitor function in patients with swelling or abdominal pain.
Test Parameters: 1. C1 Esterase Inhibitor Functional
Pretest Condition: No fasting required. Collect serum or plasma at any time. Report symptoms like swelling or abdominal pain, and list medications like C1-inhibitor replacement.
Specimen: 2-5 mL serum (SST) or 2-4 mL plasma (NaCit). Centrifuge within 1 hour. Transport in a biohazard bag within 8 hours.
Sample Stability at Room Temperature: 8 hours
Sample Stability at Refrigeration: 7 days
Sample Stability at Frozen: 6 months
Medical History: Document swelling episodes, abdominal pain, or family history of hereditary angioedema. Include current medications, especially C1-inhibitor therapy.
Consent: Written consent required, detailing the tests purpose, diagnostic implications, and potential need for C1-inhibitor replacement therapy.
Procedural Considerations: Uses an immunoassay to measure C1-inhibitor function. Results are available in 3-5 days, supporting clinical decisions.
Factors Affecting Result Accuracy: Recent C1-inhibitor therapy or improper storage can affect results. Hemolysis may degrade samples.
Clinical Significance: Reduced C1-inhibitor function confirms hereditary angioedema, prompting replacement therapy. Normal function suggests alternative diagnoses.
Specialist Consultation: Consult an allergist for result interpretation. An immunologist referral is advised for complex cases.
Additional Supporting Tests: C1-inhibitor quantitative test, C4 complement test, or genetic testing to confirm hereditary angioedema.
Test Limitations: False negatives may occur with recent therapy. Results require clinical correlation.
References: AAAAI HAE Guidelines, 2023; Journal of Allergy and Clinical Immunology, Zuraw BL, 2022.
