Renal nitrate clearance in chronic kidney disease.

•Total urinary nitrate excretion falls as renal function falls.•Renal nitrate clearance declines as renal function falls.•Fractional excretion of nitrate appears to decline as renal function falls suggesting avid retention of nitrate by the kidney when NO bioavailability is low.•Twenty 4 h urinary nitrate excretion is not a reliable measure of whole body NO synthesis.