High molecular weight glucagon-like immunoreactivity in plasma.

An "interference factor" has been shown to be present in human plasma, which can cause artifactual elevation of pancreatic glucagon values as conventionally determined by radioimmunoassay using antiserum 30K. A method of correcting for this problem was developed and used to measure glucagon levels in 60 diabetic and 30 nondiabetic subjects. No significant difference was found between the two groups. Twelve percent of the diabetic subjects had evidence of glucagon binding in their plasma which prevented valid measurement of their glucagon levels. Characterization of the "interference factor" was undertaken with G-200 sephadex column chromatography. Large amounts of glucagon-like immunoreactivity were found in fractions indicating an approximate molecular weight of 160,000. It was demonstrated that this "factor" was not an artifact of charcoal treatment of plasma. The original source of this material is unknown.