The microtiter plate provided in this kit has been pre-coated with a goat-anti-rabbit antibody. Standards or samples are then added to the appropriate microtiter plate wells with a HRP-conjugated APC and antibody preparation specific for APC and incubated. Then substrate solutions are added to each well. The enzyme-substrate reaction is terminated by the addition of a sulphuric acid solution and the color change is measured spectrophotometrically at a wavelength of 450 nm +/- 2 nm. The concentra