Clinical kidney biopsies variably contain cortex and medulla depending on biopsy depth and angle. Therefore, biopsy composition may alter the transcriptional profile and confound conclusions drawn from differential gene expression analysis. To account for this in retrieval biopsies, we assessed differences in gene expression between paired cortex and medulla samples in n=5 human kidneys. Overall design: Comparative gene expression profiling analysis of RNA-seq data kidney biopsies taken from cortex and medulla