Analysis of glucagon-like peptide 1; what to measure?

BackgroundGlucagon-like peptide 1 (GLP-1) is a gut hormone which acts as an incretin and is therefore of major interest in treatment of type II diabetes mellitus. GLP-1 circulates in many different forms, some of which are biologically active and others are not. Our hypothesis was that various methods to measure GLP-1 detect different forms of GLP-1, which may cause confusion when comparing results.MethodsWe compared three assays, the GLP-1 (active) ELISA (Linco research; ELISALINCO), GLP-1 (total) RIA (Linco research; RIALINCO) and the total GLP-1 RIA developed by the group of Holst (RIAHOLST) on specimens obtained during meal studies. In addition, we studied the effect of addition of a DPP-4 inhibitor.ResultsThe correlation between RIALINCO and ELISALINCO was highest (r = 0.76; n = 35; p < 0.01), whereas results of RIAHOLST correlated less with those of RIALINCO and ELISALINCO (r = 0.35 and 0.39 respectively; n = 35; p < 0.05). GLP-1 results measured with ELISALINCO were higher (median 28%; p < 0.001) upon addition of the DPP-4 inhibitor.ConclusionTwo commercially available GLP-1 assays do not necessarily give results equal to the well-defined GLP-1 assay developed in Copenhagen. Absolute values are also different due to differences in standardisation. Moreover, assays detect different forms of GLP-1, which hampers comparison to published data.