Evaluating Functional C1INH with Multiple Laboratory Methods across Hereditary Angioedema Types Functional C1INH in HAE: Multiple Techniques

Maine Luellah Demaret Bardou^1*Rosemeire Navickas Constanitno-Silva¹Maria Luiza Oliva Alonso²Ana Júlia Ribeiro Teixeira³Pedro Francisco Giavina-Bianchi³Eli Mansour⁴Joao Bosco Pesquero⁵Solange Oliveira Rodrigues Valle²Anete Sevciovic Grumach¹

• ¹Faculdade de Medicina do ABC, Santo André, Brazil
• ²Universidade Federal do Rio de Janeiro Hospital Universitario Clementino Fraga Filho, Rio de Janeiro, Brazil
• ³Universidade de Sao Paulo, São Paulo, Brazil
• ⁴Universidade Estadual de Campinas Faculdade de Ciencias Medicas, Campinas, Brazil
• ⁵Universidade Federal de Sao Paulo, São Paulo, Brazil

Introduction: Hereditary angioedema (HAE) is a rare genetic disease characterized by recurrent episodes of edema and classified into HAE with C1 inhibitor deficiency (HAE-C1INH types 1 and 2) and HAE with normal C1INH (HAE-nC1INH). This study evaluates the function of C1 inhibitor functional of C1 inhibitor (fC1INH) in patients with suspected HAE using several laboratory methods: DBS (dried blood spot), chromogenic assay and ELISA with FXIIa and PKa (plasma kallikrein). The comparative approach aims to improve early detection and understanding of C1INH dysfunction in all HAE subtypes to reflect real-world diagnostic scenarios.We assessed the diagnostic performance of four fC1INH assays in a cohort of 148 HAE patients: 84 with HAE-C1INH (72 Type 1 and 12 Type 2) and 64 with HAE-nC1INH (53 HAE-FXII and 11 HAE-UNK). The gold-standard chromogenic assay and the two substratespecific ELISAs (PKa and FXIIa) were compared to a novel DBS-based LC-MS/MS assay using endogenous C1s activity. For all fC1INH assays, values >50% were considered within the normal range.In HAE-C1INH, the DBS assay showed the highest specificity (Type 1: 98.6%, Type 2: 100%) and 100% sensitivity for both subtypes. ELISA-FXIIa also performed well (specificity: 97.2% and 91.7%). In contrast, ELISA-PKa and the chromogenic assay showed reduced specificity in Type 2 (25% and 66.7%, respectively). Among patients with HAE-FXII, fC1INH levels were reduced by 36.5% by ELISA-FXIIa (19/52), 19.1% by DBS (9/47), and 3.8% by ELISA-PKa (2/52), no alterations were detected by the chromogenic assay. Some of the changes seen in other tests may be partly related to pregnancy in few patients. In the HAE-UNK group, all 11 patients had fC1INH >50% in all methods.DBS-based LC-MS/MS and ELISA-FXIIa offer promising accuracy and broader applicability for early diagnosis of HAE types 1 and 2. The use of novel substrates and inclusion of a clinically realistic cohort may enhance the translational relevance of these findings.