If all the citrate in the kidney were metabolized, it would provide 10% of the renal energy requirement.14Renal TransportIn serum, the concentration of citrate is relatively constant, ranging from 0.05 mM to 0.3 mM.15 The majority of citrate exists complexed to divalent ions, such as calcium and magnesium, and is filtered freely at the glomerulus; reabsorption takes place predominantly in the prox