MEASUREMENTS OF RENAL FUNCTION Most previous RCTs have measured changes in serum creatinine concentration rather than any direct measures of renal failure. Serum creatinine concentration can provide information on GFR. However, it is not accurate since it is affected by diet, aging and muscle mass. Furthermore, acetylcysteine also lowers serum creatinine concentration itself, suggesting that the lower creatinine noted in the RCTs may not actually reflect improved renal function. GFR is the best marker of global renal function. It can be directly measured using the 51Cr−EDTA method but this is a complicated technique. We will use an alternative method by measuring plasma clearance of inulin. Serum cystatin C concentration may be a better marker of GFR than creatinine. Cystatin C is a small cysteine protease that is secreted at a fixed rate by all nucleated cells and is not affected by diet or muscle mass. In RCIN, serum cystatin concentration peaks and normalises more rapidly than creatinine. We will measure cystatin C in these patients to assess whether it would be a better marker of GFR in future RCTs.