Plasma with Added Protease Inhibitors Improves Alpha- and Beta-CGRP Measurement Compared to Serum: Towards a Reliable Biomarker for Chronic Migraine.

The neuropeptide calcitonin gene-related peptide (CGRP), especially α-CGRP, is central in migraine pathophysiology. Although CGRP is a therapeutic target and potential biomarker, inconsistencies in measurement procedures need to be further studied for reliable results. This study aims to analyze factors influencing plasma CGRP measurement. Chronic migraine (CM) patients were recruited in our Headache Unit. Blood samples were collected before and during treatment with CGRP monoclonal antibodies, processed and stored. Levels of CGRP were measured with isoform-specific enzyme-linked immunosorbent assay (ELISA) tests. Statistical tests were used to assess concentration changes and group differences. The addition of protease inhibitors (PIs) to plasma samples significantly increased α-CGRP level detection, with a smaller effect on β-CGRP. No correlation was found between the α- and β-CGRP levels in plasma. The plasma-PI samples showed higher CGRP concentrations than in serum. The α-CGRP levels decreased during treatment while the β-CGRP levels remained stable. α-CGRP and age correlated negatively, but no sex-related differences were observed either for α- or β-CGRP. PI improved CGRP detection in plasma. The α-CGRP levels, which were influenced by age, decreased with specific treatment, suggesting its potential role as a biomarker. In contrast, β-CGRP remained stable, suggesting independent regulation of both isoforms.