PRT/H antibody cross-reactivity with NPH insulin. Plasma from 32 CPB patients with high PRT/H antibody reactivity (A_450nm >3.0) was analyzed for reactivity by ELISA on microtiter plates coated with NPH insulin, which contains protamine (diluted 1:160 in PBS), and with regular insulin, which does not contain protamine (diluted 1:160 in PBS; P = < .0001). Each symbol represents an individual CPB patient.