Tin A, et al. - In participants of the African American Study of Kidney Disease and Hypertension (AASK), researchers assessed the links between the number of APOL1 risk alleles and 760 serum metabolites identified via untargeted profiling. They also replicated findings in 678 black participants with CKD in BioMe, an electronic medical record–linked biobank. They tested the metabolite association with CKD progression in AASK, BioMe, and the Modification of Diet in Renal Disease (MDRD) Study. Serum 6-bromotryptophan was identified as a consistent and novel risk factor for CKD progression. In AASK and BioMe participants and in white participants in the MDRD Study, lower levels of 6-bromotryptophan were found to be related to CKD progression, independent of demographics and clinical characteristics, including baseline GFR.