Discrepancy of fasting plasma glucagon levels measured by different glucagon antisera

To investigate the possible discrepancy between immunoreactive glucagon (IRG) levels measured by two glucagon-specific antisera, OAL-123 and 30K, fasting plasma IRG levels were measured in 30 diabetics (DM group), 56 patients with impaired glucose tolerance (IGT group) and 96 normal subjects (normal group). The fasting plasma IRG measured by OAL-123 (OAL-IRG) in DM, IGT and normal groups were 121 +/- 53, 125 +/- 43 and 119 +/- 57 pg/ml, whereas the fasting plasma IRG measured by 30K (30K-IRG) were 109 +/- 92, 92 +/- 44 and 91 +/- 68 pg/ml, respectively. There was no significant difference in the distribution of the fasting IRG levels among DM, IGT and normal groups. Although there was a statistically significant correlation between OAL- and 30K-IRG, their correlation coefficient was as small as 0.29, and 31 of 182 cases showed a large discrepancy exceeding 100 pg/ml between the two IRG values. The OAL- and 30K-IRG measured again six months later did not show a significant change, where the first and second IRG levels showed a good correlation (0.72 and 0.83 for OAL- and 30K-IRG, both p less than 0.001). The gel chromatography of the 14 plasma with fasting OAL-IRG higher than 200 pg/ml showed that the main contributor to the fasting IRG was the component of big plasma glucagon (BPG). These data suggest that there is a significant discrepancy in the fasting plasma IRG levels measured by the different glucagon antisera and that the discrepancy is caused by the different immunoreactivity of BPG to the different glucagon antisera.