Evaluation of measured and calculated creatinine clearances as glomerular filtration markers in different stages of liver cirrhosis

Background: Discrepant results have been published regarding the suitabilit y of creatinine clearance (C-Cr) as a measure of glomerular filtration rate (GFR) in cirrhotic patients with normal renal function. Subjects and metho ds: In this study we evaluated the accuracy and precision of measured and c alculated C-Cr as indexes of GFR by comparing their values to those of inul in clearance (C-In) in 10 healthy subjects and 20 patients with either Chil d's class A or Child's class C liver cirrhosis. Results: The accuracy and p recision of GFR estimates obtained by measuring C-Cr were good in all three study groups. The mean values of the C-Cr/C-In ratio were 1.05, 1.03 and 1 .04, respectively, and the corresponding coefficients of variations were 2. 9, 2.9 and 3.8%. A close correlation between C-Cr and C-In was also found i n each study group (r = 0.98, 0.99 and 0.97, respectively, with p < 0.001 i n each case). C-Cr calculated from serum creatinine by means of the Cockcro ft-Gault formula (predicted GFR) proved to be a suitable measure of GFR in normal subjects and patients with Child's class A cirrhosis: the predicted- to-true GFR ratios were 0.93 and 0.94, respectively, CV was 12% in both cas es. Moreover, a significant correlation between predicted and true GFR was observed in both groups (r 0.73, p < 0.02 and r = 0.69, p < 0.025, respecti vely). On the contrary, in Child's class C cirrhotics, calculated C-Cr sign ificantly over-estimated GFR (predicted-to-true GFR ratio 1.23, CV 20%) and no significant correlation was found between predicted and true GFR (r = 0 .58, p > 0.05). Conclusion: In conclusion, this study shows that measured C -Cr is a reliable index of GFR in cirrhotic patients, irrespective of the d egree of liver dysfunction. Calculated C-Cr is still an adequate marker of GFR in patients with compensated liver cirrhosis, whereas it overestimates GFR in patients with decompensated cirrhosis. A lower muscle mass, a reduce d ability to convert creatine to creatinine, and the presence of ascites ar e most likely responsible for the overestimation of GFR by the Cockcroft-Ga ult formula in the latter patients.