[Quick radioimmunoassay for plasma immunoreactive insulin (IRI)--application for localizing occult insulinoma during...

A quick RIA for IRI was developed which can be applied for localizing occult insulinoma during extirpation of the tumor. We used anti-insulin antibody insolubilized with bacterial cell wall. The standard solutions were prepared by dissolving porcine insulin in human plasma containing low level of IRI. By use of this assay IRI in plasma samples are assayed within 45 min for 20 samples including standard samples. The coefficient of variation of intra- and inter-assay were 9-19% and the recovery tests were 70-120%. The assay has a sensitivity of 10 microU/ml. The obtained IRI values by this method correlated well with those by the usual method (Insulin RIA Bead) (y=1.0 x -0.2, r = 0.98). A clinical case with insulinoma was shown in which the localization of the tumor was diagnosed from IRI levels in various portions of splenic vein assayed by this method during the operation and the tumor was extirpated successfully.