GFR in patients with β-thalassemia major

Background and objectives Patients with β-thalassemia major (TM) may have tubular dysfunction and glomerular dysfunction, primarily hyperfiltration, based on eGFR. Assessment of GFR based on serum creatinine concentration may overestimate GFR in these patients. This study sought to determine GFR by using inulin clearance and compare it with measured creatinine clearance (Ccr) and eGFR. Design, setting, participants & measurements Patients followed up in an Israeli thalassemia clinic who had been regularly transfused for years and treated with deferasirox were included in the study. They were studied by inulin clearance, Ccr, the CKD Epidemiology Collaboration and the Modification of Diet in Renal Disease equations for eGFR, and the Cockcroft–Gault estimation for Ccr. Expected creatinine excretion rate and tubular creatinine secretion rate were calculated. Results Nine white patients were studied. Results, given as medians, were as follows: serum creatinine was 0.59 mg/dl (below normal limits); GFR was low (76.6 ml/min per 1.73 m²) and reached the level of CKD; Ccr was 134.9 ml/min per 1.73 m², higher than the GFR because of a tubular creatinine secretion rate of 30.3 ml/min per 1.73 m² (this accounted for 40% of the Ccr); and eGFR calculated by the CKD Epidemiology Collaboration and Modification of Diet in Renal Disease equations and Cockcroft–Gault–estimated Ccr were 133, 141, and 168 ml/min per 1.73 m², respectively. These latter values were significantly higher than the GFR, reaching the hyperfiltration range, and indicated that the estimation techniques were clinically unacceptable as a method for measuring kidney function compared with the GFR according to Bland and Altman analyses. Conclusions Contrary to previous reports, patients in this study with TM had normal or reduced GFR. The estimating methods showed erroneous overestimation of GFR and were clinically unacceptable for GFR measurements in patients with TM by Bland and Altman analysis. Therefore, more accurate methods should be used for early detection of reduced GFR and prevention of its further decline toward CKD in these patients.