Creatinine excretion after renal transplantation.

For alterations in serum creatinine to reflect changes in GFR, urine creatinine excretion must remain constant. Although serum creatinine is often used to monitor chronic changes in allograft GFR, creatinine excretion has not been systematically investigated in renal transplant recipients. In the present study, creatinine excretion was examined in 100 patients who survived at least 12 months with functioning renal allografts. Overall, there was a progressive decline in creatinine excretion from 1420 +/- 410 mg/24 hr at 3 months to 1240 +/- 394 mg/24 hr at last follow-up, 89 +/- 35 months after transplantation (mean +/- SD). The decline in creatinine excretion was greatest in those who subsequently returned to dialysis (-27.4 +/- 20.2%, P less than .05) compared with those who died (-6.9 +/- 24.1%), or survived with functioning allografts (-3.7 +/- 18.1%). Multivariate analysis demonstrated that age, sex, body weight, obesity, diabetes, and cumulative average daily corticosteroid dose (factors that affect muscle mass) all influenced creatinine excretion. However, early post-transplant clinical parameters failed to predict patients who subsequently had declines in creatinine excretion. Thus, it was not possible to predict patients in whom chronic changes in allograft function would be underestimated by changes in serum creatinine. Although clinically relevant functional alterations can be detected by changes in serum creatinine, additional measures of GFR should be used to complement the serum creatinine and monitor chronic changes in allograft function after renal transplantation.