Protocol core needle biopsy and histologic Chronic Allograft Damage Index (CADI) as surrogate end point for long-term graft survival in multicenter studies

Abstract

This study is an investigation of whether a protocol biopsy may be used as surrogate to late graft survival in multicenter renal transplantation trials. During two mycophenolate mofetil trials, 621 representative protocol biopsies were obtained at baseline, 1 yr, and 3 yr. The samples were coded and evaluated blindly by two pathologists, and Chronic Allograft Damage Index (CADI) score was constructed. At 1 yr, only 20% of patients had elevated (>1.5 mg/100 ml) serum creatinine, whereas 60% of the biopsies demonstrated an elevated (>2.0) CADI score. The mean CADI score at baseline, 1.3 ± 1.1, increased to 3.3 ± 1.8 at 1 yr and to 4.1 ± 2.2 at 3 yr. The patients at 1 yr were divided into three groups, those with CADI <2, between 2 and 3.9, and >4.0, the first two groups having normal (1.4 ± 0.3 and 1.5 ± 0.6 mg/dl) and the third group pathologic (1.9 ± 0.8 mg/dl) serum creatinine. At 3 yr, there were no lost grafts in the low CADI group, six lost grafts (4.6%) in the in the elevated CADI group, and 17 lost grafts (16.7%) in the high CADI group (P < 0.001). One-year histologic CADI score predicts graft survival even when the graft function is still normal. This observation makes it possible to use CADI as a surrogate end point in prevention trials and to identify the patients at risk for intervention trials.