Performance of methods to assess kidney function in a predominantly overweight sample of patients with liver disease

The assessment of glomerular filtration rate (GFR) in patients with liver disease is necessary to make decisions about organ allocation. Creatinine is widely used as a marker of GFR; however, it is not reliable in patients with liver disease. The aims of this study were to (1) determine if iodine 125-labeled iothalamate ((125)I-iothalamate) clearance calculated using the plasma decay method is equal to renal clearance of (125)I-iothalamate and (2) estimate kidney function using the creatinine-based Cockcroft-Gault and the Modification of Diet in Renal Disease equations, a cystatin C-based equation, the urine collection method for creatinine clearance, and plasma clearance of vancomycin (V) and compare these estimates to renal clearance of (125)I-iothalamate in adult patients with liver disease. Adults with liver disease received (125)I-iothalamate and V and had a catheter placed for urine collection. Blood and urine samples were collected over 8 h for analysis of (125)I-iothalamate, creatinine, and V to determine kidney function. Estimates were compared to renal (125)I-iothalamate clearance. Eight patients classified as Child-Pugh class B were enrolled: age was 52 ± 6 years; body mass index was 36.5 ± 19 kg/m(2); and Model for End-Stage Liver Disease score was 13 ± 3. Mean estimates of kidney function did not differ significantly from mean renal (125)I-iothalamate clearance (74 ± 38 mL/min/1.73 m(2)). Other methods overestimated kidney function at lower levels of GFR (<60 mL/min/1.73 m(2)) and underestimated kidney function at higher GFR levels. Given the variability in performance of methods to assess kidney function in this population, direct measurement of GFR may be preferable to indirect estimates based on marker compounds such as creatinine and cystatin C until more accurate methods are developed.