Quantifying Insulin Residue on Catheter Membranes

Catheter membranes from seven of the eleven subjects were analyzed for insulin residue (Fig. 1). The frozen membranes were thawed at room temperature. 50 µL phosphate buffered saline (PBS) (Medicago AB, Uppsala, Sweden) with 0.05% Tween 20 (Bio-Rad, California, USA) was added to each vial. After an incubation overnight at 4 °C, the vials were placed on a plate shaker with occasional mixing at room temperature for four hours to extract the adsorbed proteins from the membranes. This method has previously been used for detection of proteins adsorbed to the catheter membrane in surgically treated intracerebral hemorrhage patients^{19 (link)}. Insulin concentration was then measured using ultrasensitive ELISA (Mercodia AB, Uppsala, Sweden) and a Clariostar Monochromator Microplate reader with a 450 nm filter (BMG Labtech, Ortenberg, Germany).