Cystatin C and creatinine as markers for radiocontrast-induced nephropathy in patients treated with N-acetylcysteine.

The beneficial effect of N-acetylcysteine (NAC) in the prevention of radiocontrast-induced nephropathy (RCIN) as well as the definition of an adequate surrogate parameter for the evaluation of the incidence of RCIN remain points of controversial discussion. Nearly all clinical studies used an increase in serum creatinine to define renal injury, although cystatin C is suggested to be superior to creatinine in estimating glomerular filtration rate (GFR). Furthermore, a recent study showed that in healthy volunteers, NAC leads to a decrease in serum creatinine without influencing serum cystatin C concentrations, implicating a possible overestimation of the protective effect of NAC on the incidence of RCIN. We compared serum creatinine and cystatin C levels in patients with chronic kidney disease undergoing coronary angiography, as these patients are to be considered at highest risk for the development of RCIN. A total of three doses of NAC was given orally, and patients received isotonic saline intravenously. Serum levels at baseline and 24 hours after angiography were not significantly different for serum creatinine (1.72 +/- 0.08 mg/dl and 1.72 +/- 0.08 mg/dl) and for cystatin C (1.72 +/- 0.09 mg/dl and 1.76 +/-0.10 mg/dl). There was a significant positive correlation between creatinine and cystatin C serum levels before and after exposure to radiocontrast medium (p < 0.05) in all patients, including subgroup analyses. We conclude that serum creatinine and cystatin C are equivalent surrogate parameters for the evaluation of NAC in the prevention of RCIN. Furthermore, we present a prophylactic treatment regime easily applicable even in an outpatient setting, which seems to protect very effectively against RCIN in a high-risk group of patients.