A micromodification of an indirect two-site immunoradiometric assay for proinsulin is described. The assay is performed not in tubes but in disposable pipette tips. The volume of sample necessary is reduced from 50–200 μl to 10 μl. This economy is accompanied by economy of reagents. The repetitive washing steps required by each stage of the assay are considerably simplified and speeded. The time needed for completion of the assay has been reduced from 72 to 48 hours. The detection limit of the assay is unaltered at 6 pmol proinsulin/l.
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