Finally, as an external validation of the model developed to predict high-grade cancer based on kallikrein markers measured in anticoagulated plasma from 4765 biopsied ProtecT participants, we assessed the discriminatory accuracy of this model using 1364 biopsied ProtecT participants with only serum samples available to measure the four kallikrein markers and excluding 496 ProtecT participants with both anticoagulated plasma and serum samples available. Here, KLK4 is linked to cancer.