[An improved method for determination of C-peptide levels in serum: pretreatment of test samples with anti-insulin antibody insolubilized with magnetic particles].
RIA using anti-C-peptide antibody has been employed for determination of C-peptide in serum. However, the level by this method is a sum of the levels of C-peptide and proinsulin, because anti-C-peptide cross-reacts with proinsulin. This time we developed an improved assay for C-peptide, in which a test sample is pretreated with anti-insulin antibody to eliminate proinsulin in samples before C-peptide assay. The assay procedure is composed of 3 steps; the first is the incubation of test serum with anti-insulin antibody insolubilized with magnetic particles to form a complex of proinsulin-anti-insulin antibody, the 2nd step is the centrifugation of the mixture to eliminate the complex and the last step is the assay for C-peptide by use of RIA kit in the supernatant. The assay is simple, sensitive and reproducible. Serum C-peptide level by this method is not influenced by the presence of proinsulin in test serum, even when as high as 9 ng/ml of proinsulin is contained. This assay revealed that a patient with insulinoma had normal level of serum C-peptide in spite of the extremely high level of proinsulin.
Sasakuma
F
F
Department of Laboratory Medicine, Center for Adult Diseases, Osaka.
Shimizu
T
T
Ishikawa
O
O
Hasegawa
K
K
Kitamura
H
H
Matsumiya
K
K
Doi
K
K
Kojima
J
J
D002096:C-Peptide / Q000097:blood*; D005069:Evaluation Studies as Topic; D006801:Humans; D007340:Insulinoma / Q000175:diagnosis; D010190:Pancreatic Neoplasms / Q000175:diagnosis; D011863:Radioimmunoassay / Q000379:methods*; D011933:Reagent Kits, Diagnostic / Q000592:standards*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D002096:C-Peptide; D011933:Reagent Kits, Diagnostic