Assay-related Differences in SuPAR Levels: Implications for Measurement and Data Interpretation

With the growing interest in studying the role of soluble urokinase plasminogen activator receptor (suPAR) in kidney and other diseases, levels are now being measured in major cohorts across the world through various methods, including immunoassays and through proteomics. Reported suPAR values have however varied dramatically depending on which assay is used. Comparing suPAR assays and their ability to discriminate risk is crucial for the Nephrology and overall research community to guide assay choice and inform interpretation of findings. To that end we measured suPAR in 3 different major cohorts (Malmo Diet and Cancer Study, n=4637; Jackson Heart Study, n=1905; and the Emory Cardiovascular Biobank, n=487) using two different methods in each cohort, encompassing the most commonly used approaches (immunoassays and proteomics). We find dramatic differences between assays; with notably poor correlations between immunoassays and proteomic approaches (r=0.2-0.5). Proteomics-based suPAR measures very poor discriminatory ability for cardiovascular and incident kidney disease. Amongst the immunoassays, the suPARnostic assay reported the highest values and had the strongest discriminatory ability.