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

BACKGROUND: Glucagon-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. METHODS: We compared three assays, the GLP-1 (active) ELISA (Linco research; ELISA(LINCO)), GLP-1 (total) RIA (Linco research; RIA(LINCO)) and the total GLP-1 RIA developed by the group of Holst (RIA(HOLST)) on specimens obtained during meal studies. In addition, we studied the effect of addition of a DPP-4 inhibitor. RESULTS: The correlation between RIA(LINCO) and ELISA(LINCO) was highest (r=0.76; n=35; p<0.01), whereas results of RIA(HOLST) correlated less with those of RIA(LINCO) and ELISA(LINCO) (r=0.35 and 0.39 respectively; n=35; p<0.05). GLP-1 results measured with ELISA(LINCO) were higher (median 28%; p<0.001) upon addition of the DPP-4 inhibitor. CONCLUSION: Two 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.

Performance of free beta-human chorionic gonadotrophin (free beta-hCG) and pregnancy associated plasma protein-A (PAPP-A) analysis between Delfia Xpress and AutoDelfia systems in The Netherlands.

BACKGROUND: The VU University Medical Center (VUmc) was the first hospital in the Netherlands to introduce the Delfia Xpress for the analysis of free beta-human chorionic gonadotrophin (beta-hCG) and pregnancy associated plasma protein-A (PAPP-A) in the first trimester screening program for Down syndrome. Since then, others have implemented this system. In this study, we tested the equality of measurements for free beta-hCG and PAPP-A between Delfia Xpress systems and one AutoDelfia system. METHODS: A total of 40 serum samples were aliquoted and stored at -20 degrees C. Samples were analyzed by six Delfia Xpress systems and one AutoDelfia system over a time period of 2 years. RESULTS: The relationships between free beta-hCG and PAPP-A were excellent for the different Delfia Xpress systems (r>0.99, p<0.0001). For PAPP-A, the agreement between the main system at VUmc and five other systems was linear with slopes between 0.99 and 1.06. Similarly, agreement for free beta-hCG was linear with slopes between 0.99 and 1.09. Likewise, agreement for PAPP-A and free beta-hCG was excellent for the AutoDelfia vs. the main Delfia Xpress at the VUmc (r>0.99, p<0.0001). For both PAPP-A and free beta-hCG, the relationships were linear with slopes of 1.08 and 1.07. CONCLUSIONS: We demonstrate an excellent agreement for the analysis of PAPP-A and free beta-hCG between Delfia Xpress systems and one AutoDelfia system.