MPA should be added to fresh samples prior to sample handling or sample storage. That is required to deproteinize samples in order to preserve the integrity of the biological marker and to ensure reliable data. Note that 5% MPA will interfere with the assay. Upon preparing samples, each sample must be diluted at least 1:10 with 1X Assay Buffer to bring the MPA final concentration to 0.5%. Some samples may need to be diluted more. Make serial dilutions of samples as necessary to obtain a quantifiable change in absorbance readings over time.