Relationship Between Albuminuria During the First Year and Antibody-Mediated Rejection in Protocol Biopsies in Kidney Transplant Recipients

Background. Antibody-mediated rejection is the main cause of deterioration of kidney transplants and frequently is detected only by means of protocol biopsies. The aim of this study was to relate the presence of albuminuria throughout the 1st year to the histologic findings detected by 1-year protocol biopsies in kidney graft recipients. Methods. Retrospective observational study of 86 protocol biopsies 1 year after transplantation. Albuminuria was measured at 3, 6, 9, and 12 months in urine samples and expressed as albumin/creatinine (mg/g). Results. Analysis of biopsies, reflected according to the Banff criteria, the following categories: fibrosis and tubular atrophy, 35 (40.7%); cellular rejection, 13 (15.1%); antibody-mediated rejection, 8 (9.3%); chronic glomerulopathy, 10 (11.6%); normal, 14 (16.3%); recurrence, 1 (1.2%); and other, 5 (5.8%). The proportions of patients with albuminuria for Banff scale scores (0 vs >= 1, respectively) at 6 and 12 months, respectively, after transplantation, were: for marker glomerulitis, 45.5% versus 59.3% (P = .021) and 36.4% versus 70.4% (P < .001); for marker glomerulopathy, 49.1% versus 50.0% (P = .051) and 42.1% versus 58.3% (P = .019); for marker peritubular capillaritis, 45.8% versus 60.9% (P = .047) and 39.0% versus 69.6% (P = .276); and for marker C4d, 49.2% versus 56.3% (P = .894) and 46.2% versus 56.3% (P = .774). Conclusions. The presence of albuminuria after renal transplantation is common, especially in patients with proteinuria. Persistent albuminuria after transplantation, even at low levels, can be indicative of subclinical antibody-mediated rejection. Additional broader studies to relate the albuminuria to histologic changes observed in protocol biopsies are required.