Improved estimation of glomerular filtration rate by serum cystatin C in preventing contrast induced nephropathy by N-acetylcysteine or zinc--preliminary results

BACKGROUND: Prevention of contrast media (CM) induced nephropathy (CIN) by prophylaxis (e.g. N-acetylcysteine; NAC) is controversially discussed. Up to now, assessment of kidney function has been based on measurements of serum creatinine, although this biomarker has several limitations. We investigated NAC and zinc (Zn) for the prevention of CIN by monitoring creatinine and cystatin C. METHODS: In a prospective, placebo-controlled, double blind trial, patients with moderately impaired kidney function receiving low-osmolar, non-ionic CM were randomly assigned to an oral treatment for 2 days with 1.2 g/day of NAC (n = 19), for 1 day with 60 mg/day of Zn (n = 18) or placebo (n = 17). All patients received peri-procedurally 1 ml/kg/h of 0.45% saline for 24 h. At baseline, prior to exposure of CM, 2 and 6 days after CM, creatinine and cystatin C were measured. RESULTS: There was no difference in the incidence of CIN, but a significant drop in creatinine (P < 0.05) was observed in all patients during volume expansion. Creatinine showed no increase after CM and it was normalized to the baseline values in all groups at the study end. In contrast, 2 days after CM there was a significant rise in cystatin C in the Zn (P = 0.012) and the placebo (P = 0.041) group, whereas NAC prevented this deterioration of kidney function. CONCLUSIONS: Cystatin C seems to reflect CM-induced changes in kidney function better than creatinine. NAC and Zn have no effect in preventing CIN by the standard definition, but based on cystatin C we can confirm a preventive effect of NAC. It appears mandatory to assess kidney function by cystatin C in CIN intervention trials, because relying on creatinine can be misleading.