Estimation of renal function changes on the basis of serum creatinine levels - potential and limitations
Abstract
Introduction: In daily practice, changes of renal function are most commonly evaluated in the basis of serum creatinine (SCr) concentration. In this study, we tried to investigate if and how accurately SCr changes can be used to evaluate changes in renal creatinine clearance (CCr), and glomerular filtration rate (GFR) estimated on the basis of MDRD (Modification of Diet in Renal Disease) formula and accurately measured by renal inulin clearance (Cin).
Methods: In 32 patients suffering from chronic renal disease, with average SCr 202 (60-564) µmol/l, Cin was repeatedly measured and GFR was calculated on the basis of SCr and other parameters needed according to the MDRD formula. Relationships between a difference or SCr ratio found in the beginning (SCr)0 and the end of the study (SCr)t with appropriate values of Cin a MDRD were investigated.
Regression analysis and the Bland-Altman analysis were used as a statistical tool. Results: A highly significant linear relationship between values of (SCr)0/(SCr)t and (MDRD)t/(MDRD)0 was found (r=0,968; p<0,000).
Evaluation of changes of GFR on the basis of (SCr)0/(SCr)t ratio yields equivalent information as evaluation of (MDRD)t/(MDRD)0 ratio. A significant linear dependence between values of (SCr)0/(SCr)t and (Cin)t/(Cin)0 were found, however the value of the correlation coefficient is substantially lower (r=0,474; p<0,000).
Only greater changes of Cin can be evaluated on the basis of (SCr)0/(SCr)t. Conclusions: A difference in creatinine serum concentrations (SKr)t - (SKr)0 allows us to evaluate deterioration or amelioration of renal function, however a quantitative change of renal function cannot be determined.
The (SCr)t/(SCr)0 ratio enables a quantitative change of CCr, however such an evaluation is not easy, while the relationship between (SCr)t/(SCr)0 and (CCr)t/(CCr)0 is hyperbolic. Evaluation of the reciprocal value of (SCr)t/(SCr)0, i.e. (SCr)0/(SCr)t ratio is simpler, because the relationship between this value and both estimated and measured GFR is linear.
This method enables the evaluation of renal function decrease as a percentage of initial value.