The most important analyte used to verify the cleanliness of a medical device after a cleaning process is protein [1, 2]. There are a variety of different Assays to test for protein, the most commonly used Assays are based on ortho-phthalaldehyde (OPA) and bicinchoninic acid (BCA) [2]. In this study 42 different cleaning detergents from 14 different manufacturers were tested for their potential to influence the output of these Assays.