Enhanced quantification of α-cell suppression by hyperglycemia using a high-sensitivity glucagon assay.

Accurate measurement of glucagon concentrations in a variety of conditions is necessary for subsequent estimation of glucagon secretion. Glucagon arises in the α-cell as a product of proglucagon processing. Modern two-site immunoassays have overcome prior problems with glucagon measurement caused by cross-reactivity with other proglucagon-derived fragments. However, in response to hyperglycemia, glucagon concentrations can fall below the limit of quantification of commercial immunoassays. This has implications for the characterization of α-cell function in health, in prediabetes, and in type 2 diabetes. An increase in the sensitivity of glucagon measurement was achieved by ethanol precipitation and concentration of the sample before measurement. Concentrating the sample sixfold enabled a decrease in the level of quantitation from 1.7 to 0.3 pmol/L with acceptable precision. To establish whether this enhanced high-sensitivity glucagon assay enhances the characterization of α-cell function in health and disease, we then estimated glucagon secretion rate (GSR) in four subjects. We subsequently used the relationship of GSR to glucose concentrations to characterize the α-cell response to glucose and demonstrate improved characterization of α-cell dysfunction in vivo. We describe a method that lowers the limit of quantification of a glucagon immunoassay thereby enhancing the ability to differentiate between normal and abnormal α-cell responsiveness to glucagon.