Renal functional assessment in the failing renal graft: what to do where clearances show discrepancy

Recently increased attention for chronic renal failurehas stimulated new interest in renal function assess-ment by direct measurement as well as by algorithmsor formulas [1–3]. In the failing renal graft, a situationin which pharmacological therapy may interfere withthe complex adaptation mechanisms of renal failure,the assessment of renal function may be particularlydifficult [4]. Studies of patients with liver or hearttransplantation and advanced kidney disease suggestthat creatinine-based indexes may be poor indicatorsof residual renal function under calcineurin inhibitors[5,6]. The following two cases, displaying a discrepancybetween creatinine and urea clearances, draw attentionto this rather neglected, yet clinically relevant, aspectof renal function assessment.