In a single-centre , prospective study of 70 patients ( 74 9 ys ; range 47-85 ys ; 77 % male ) , cystatin C was measured six times : ( T1 = preoperative , T2 = start cardiopulmonary bypass ( CPB ) , T3 = 20 min after CPB , T4 = end of operation ; T5 = 24 h postoperatively ; T6 = 7d postoperatively ) .