Comparison of estimated glomerular filtration rates from serum creatinine and cystatin C in patients with impaired creatinine production.

Determination of the glomerular filtration rate (GFR) is important for the drug dosage adjustment and clinical management of patients. The aim of our study was the comparison of estimated GFR values from serum creatinine (eGFRcreatinine) and cystatin C (eGFRcystatin C) in patients with impaired creatinine production. A total of 564 serum samples from patients with kidney disease (n=179), liver (n=71) and kidney (n=182) transplants, critically ill patients (n=82) and healthy subjects (n=50) were analyzed for serum creatinine and cystatin C. The creatinine production rate (CPR) was significantly lower in the different groups of patients than in the control group (p<0.001). A negative correlation was found between the eGFRcreatinine/eGFRcystatin C ratio and CPR (r= -0.964, p<0.001). For CPR higher than 800 mg/24h both procedures for estimating the GFR classified values higher and lower than 60 mL/min with an acceptable agreement; however, for CPR less than 800 mg/24h the eGFRcreatinine led to false negatives in a high number of cases with eGFRcystatin C <60 mL/min.