Specificity and sensitivity of commercially available assays for glucagon-like peptide-1 (GLP-1): implications for GLP-1 measurements in clinical studies

Authors

  • M. J. Bak,

    1. NNF Center for Basic Metabolic Research, Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
    2. Department of Human Nutrition, Faculty of Science, University of Copenhagen, Copenhagen, Denmark
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  • N. J. Wewer Albrechtsen,

    1. NNF Center for Basic Metabolic Research, Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
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  • J. Pedersen,

    1. NNF Center for Basic Metabolic Research, Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
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  • F. K. Knop,

    1. Diabetes Research Division, Department of Medicine, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark
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  • T. Vilsbøll,

    1. Diabetes Research Division, Department of Medicine, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark
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  • N. B. Jørgensen,

    1. Department of Endocrinology, Hvidovre Hospital, University of Copenhagen, Hvidovre, Denmark
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  • B. Hartmann,

    1. NNF Center for Basic Metabolic Research, Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
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  • C. F. Deacon,

    1. NNF Center for Basic Metabolic Research, Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
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  • L. O. Dragsted,

    1. Department of Human Nutrition, Faculty of Science, University of Copenhagen, Copenhagen, Denmark
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  • J. J. Holst

    Corresponding author
    1. NNF Center for Basic Metabolic Research, Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
    • Correspondence to: Prof. Jens Juul Holst, Department of Biomedical Sciences, The Panum Institute, University of Copenhagen, Blegdamsvej 3, building 12.2, DK-2200 Copenhagen N, Denmark.

      E-mail: jjholst@sund.ku.dk

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Abstract

Aims

To evaluate the performances of commercially available glucagon-like peptide-1 (GLP-1) assays and the implications for clinical studies.

Methods

Known concentrations (5–300 pmol/l) of synthetic GLP-1 isoforms (GLP-1 1-36NH2, 7-36NH2, 9-36NH2, 1-37, 7-37 and 9-37) were added to the matrix (assay buffer) supplied with 10 different kits and to human plasma, and recoveries were determined. Assays yielding meaningful results were analysed for precision and sensitivity by repeated analysis and ability to discriminate low concentrations. Endogenous GLP-1 levels in clinical samples were assessed using three commercial kits.

Results

The USCN LIFE assay detected none of the GLP-1 isoforms. The active GLP-1 enzyme-linked immunosorbent assays (ELISAs) from Millipore and DRG appeared identical and were specific for intact GLP-1 in buffer and plasma. The Meso Scale Discovery (MSD) total GLP-1 kit detected all six GLP-1 isoforms, although recovery of non-active forms was incomplete, especially in plasma. Millipore total GLP-1 ELISA kit detected all isoforms in buffer, but mainly amidated forms in plasma. The Alpco, Phoenix and Bio-Rad kits detected only amidated GLP-1, but the Alpco kit had a limited measurement range (30 pmol/l), the Phoenix kit had incomplete recovery in plasma and the Bio-Rad kit was insensitive (detection limit in plasma 40 pmol/l). The pattern of postprandial GLP-1 responses in clinical samples was similar between the kits tested, but the absolute concentrations measured varied.

Conclusions

The specificity and sensitivity of commercially available kits for the analysis of GLP-1 levels vary considerably. This should be taken into account when selecting which assay to use and when comparing data from different studies.

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