Background Prevention of contrast media (CM) induced nephropathy (CIN) by pharmacological prophylaxis (e.g. N–acetylcysteine; NAC) is controversially discussed. So far, in all interventional studies assessment of kidney function was based on measurements of serum creatinine although this surrogate biomarker has several limitations. We investigated the antioxidants NAC and zinc (Zn) for the prevention of CIN by monitoring concomitantly serum levels of creatinine and cystatin C.