Evaluation of the formula clearance as a measure of the glomerular filtration rate in cyclosporin-treated children following renal transplantation

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Abstract
Since the introduction of the nephrotoxic drug, cyclosporin, as the main immunosuppressive agent following organ transplantation, the need for an accurate method to determine the glomerular filtration rate (GFR) has arisen. In the present study the clearance of inulin has been compared to the clearance of creatinine estimated by short-term urine sampling or by the formula clearance in 29 children following renal transplantation. The children, 0.4-15.4 years of age at transplantation, were examined within 5 months following transplantation, and thereafter yearly. During the first 2 years after transplantation there was poor agreement between inulin clearance and formula clearance, while 3-4 years after transplantation there was good correlation between the two methods. However, the formula clearance generally overestimated GFR and the overestimation increased with decreasing renal function. In spite of the good correlations between the two methods after the first years following transplantation, the formula clearance in individual patients does not follow the inulin clearance changes very closely. In conclusion, formula clearance was found to be an inaccurate method of following GFR, especially during the first 2 years after transplantation. This might be caused by changes in habitus as well as an increased creatinine secretion caused by cyclosporin.