1385-P: Impact of Preanalytical and Analytical Factors on Glucagon and GLP-1 Levels in Humans

Glucagon and glucagon-like peptide-1 (GLP-1) have important roles in the development and treatment of diabetes. Their plasma concentrations are currently being measured in more than 500 clinical studies according to clinicaltrial.gov. As glucagon and total GLP-1 (reflecting the secretion and action of GLP-1 and is analytically independent of DPP-4 activity) circulate in the low picomolar range it has been troublesome to accurately measure their plasma concentrations. Equally important are so-called preanalytical considerations including the use of enzyme inhibitors. The latter may also depend on the analytical approach, for example single-antibody assay versus sandwich ELISA. To provide guidelines for measurement of glucagon and GLP-1 in clinical trials we obtained blood samples using four different blood-containers (with either neprilysin inhibitor: sacubitrilat 25 µg/mL; trasylol 500KIU/mL; P800 tubes; or vehicle) from healthy individuals (male/female; 7/4; mean ± SD; age: 32 ± 12 years, BMI; 26 ± 4 kg/m²) after an overnight fast and following an intravenous amino acid (AA) infusion (14 g/L; 331 mg/min/kg body weight. Plasma concentrations of glucagon increased significantly during the AA-infusion independent of blood containers and assays. The sandwich ELISA showed significant lower levels of glucagon with addition of neprilysin inhibitor whereas both trasylol and P800 tubes resulted in increased levels during the AA-infusion. Glucagon levels measured by the two radioimmunoassays (RIA) did not depend on the containers. Levels of total GLP-1 did not depend on the containers using a sandwich ELISA (Mercodia) but increased by a factor of a 2.5 when plasma from P800 containers was assayed using a C-terminal specific RIA.

In summary, levels of glucagon and GLP-1 depend on both preanalytical and analytical factors that should be standardized for future clinical studies.