The present invention relates to compositions for improving assay accuracy for plasma samples by decreasing or eliminating false results due to platelet interference. The compositions of the present invention comprise compositions that include a platelet interference reducing agent in an amount effective to decrease the platelet interference activity in the plasma sample, particularly platelet-rich plasma sample, to be analyzed. The most preferred platelet interference reducing agent of the present invention is 1-(1,3-Bis(hydroxymethyl-2,5-dioxoimidazolidin-4-iyl)-1,3-bis(hydroxymethyl) urea, also called “Diazolidinyl urea” or “DZU”.