PREDICTING GLOMERULAR-FILTRATION RATE AFTER KIDNEY-TRANSPLANTATION

Serum creatinine is an important clinical measure of impairment of glo merular filtration rate (GFR) after kidney transplantation. The use of formulas that predict GFR (such as the Cockcroft-Gault) derived from patients with chronic renal failure and standardized against measured creatinine clearance may not be accurate when applied to kidney transp lant recipients. The purpose of this study, was to investigate the lev el of inaccuracy and its causes and then to derive predictive GFR form ulas that are appropriate to renal transplantation. Determinants of is otopic GFR, serum creatinine, and muscle mass were evaluated in consec utive kidney recipients (n=146) using Tc-99m DTPA GFR (n=751) as a ref erence method, Factors that predicted G;FR apart from serum creatinine included sex, height, body weight, serum urea, years on dialysis, num bers of rejections and infective episodes, and prednisolone dose. The relationship between serum creatinine and GFR was highly variable and dependent on factors that alter muscle mass and muscle catabolic rate, The relationship was further altered by ATN and chronic rejection whe n tubular secretion of creatinine was reduced, Three alternative GFR f ormulas (which can be applied to renal transplant patients according t o the availability of clinical parameters) were derived and tested aga inst six published methods of GFR estimation. Our derived formulas had the highest correlation, no overall bias, least scatter of sum of squ ares, and least error at low levels of GFR, They represent a better es timation of GFR in kidney transplantation than published formulas, and would allow a standardized approach to the study of longterm renal dy sfunction.