Objectives: Although it only occurs in a minority of patients, renal involvement is a life-threatening complication of scleroderma (SSc). We have investigated the utility of two formulae to calculate glomerular filtration rate (GFR) in a population of SSc patients.
Methods: Twenty-six patients (20 female, 6 male, median age 58 yr, age range 12-80 yr) satisfied our criteria for inclusion in a retrospective comparison of measured and calculated GFR. GFR was measured using (51)Cr-EDTA. The modified Cockcroft and Gault formula and equation 7 from the Modification of Diet in Renal Disease (MDRD) were used to calculate GFR.
Results: Eighteen out of 19 patients analysed with a serum creatinine concentration less than the upper limit of the normal range had a measured GFR outside the normal range. Three patients with a normal creatinine concentration had a measured GFR <60 ml/min and in each of these the calculated GFR was also abnormal. All patients with a measured GFR <60 ml/min were identified using both the MDRD and the modified Cockcroft and Gault formula to calculate GFR. The greatest correlation between measured and calculated GFR was seen when the MDRD formula, which employs demographic and serum variables, was used in patients with body surface area (BSA) >1.4 m(2) who were not taking Iloprost (r=0.91). Use of the Cockcroft and Gault formula to calculate creatinine clearance with a correction factor for GFR, the inclusion of patients taking Iloprost and the inclusion of patients with BSA <1.4 m(2) were all associated with a lower degree of correlation.
Conclusion: Serum creatinine is a poor marker of renal function in SSc patients. Calculating GFR from demographic and serum variables is a simple technique to identify SSc patients who have abnormal renal function. The authors recommend the use of the MDRD formula.