Comparison of plasma active glucagon-like peptide-1 (GLP-1) levels assayed with or without plasma extraction in non-diabetic men

Recently, interference from cross-reacting peptides in plasma has been recognized as being responsible for inter-subject differences in active glucagon-like peptide-1 (GLP-1) values. An ethanol or solid-phase extraction step could reduce such interference. A working group of the Japan Diabetes Society now recommends the inclusion of an extraction step when measuring active GLP-1 values. We measured the active GLP-1 levels of 200 specimens derived from 10 subjects using both methods and compared the results. The active GLP-1 levels measured by extraction method for 169 specimens with values greater than 2.0 pM tended to be lower than those by direct method. However, the correlation between the GLP-1 levels measured by extraction and direct method was r=0.9225 (p < 0.0001). In one case, the active GLP-1 level obtained using the extraction method was significantly lower than that obtained using the direct method. Therefore, though there is a good correlation between the two methods, extraction is recommended for more accurate active GLP-1 measurements.