The DIAsource IGF1-ELISA is a solid phase Enzyme Amplified SensitivityImmunoassay performed on polystyrene microtiterplates.In the present kit, DIAsource has introduced a pre-treatment step in order toimprove the clinical performance of the assay. It is well established that the binding proteins interfere with the ELISA assay for IGF1.The pre-treatment step used by DIAsource is the acid-ethanol procedure of Daughaday et al . A fixed amount of IGF1-labelled with horseradish peroxidase (HRP), compete with unlabelled IGF1 present in the calibrators ,controls and samples for a limited number of binding sites on a specific antibody. After 1 hour incubation at room temperature, the microtiterplate is washed to stop the competition reaction. . The Chromogenic solution (TMB ) is added and incubated for 15 min. The reaction is stopped with the addition of Stop Solution and the microtiterplate is then read at the appropriate wavelength. The amount of substrate turnover is determined colourimetrically by measuring the absorbance, which is inversely proportional to the IGF1 concentration. A calibration curve is plotted and IGF1 concentration in samples is determined by interpolation from the calibration curve.