Mean venous to arterial ratios for ~220 metabolites, ordered left to right on the x-axis from lowest to highest ratio. For any given metabolite, [V]/[A] <1 is consistent with net renal uptake, whether via filtration, secretion, and/or metabolism, whereas [V]/[A] >1 suggests net release by the kidney. Representative metabolites, including creatinine, kynurenic acid, choline, and citrulline are highlighted.