Glomerular fibrin thrombi in ABO and crossmatch compatible renal allograft biopsies.

Glomerular fibrin thrombi may be an early indication of antibody-mediated rejection in renal allograft biopsies. However, fibrin thrombi have a broad differential; thus, we sought to evaluate the etiology and implications of glomerular fibrin thrombi in allograft biopsies of blood group and cytotoxic crossmatch compatible renal allografts. Biopsies were identified from the pathology files of Oregon Health & Science University. Detailed histopathologic findings were retrospectively correlated with clinical data, treatment, and outcome. Sixteen early posttransplant biopsies had glomerular fibrin thrombi, including three surveillance biopsies. Six of 16 biopsies had no other histopathologic findings; 5/16 had glomerulitis and peritubular capillaritis; 4/16 had concomitant cellular vascular rejection; one had parenchymal infarction. C4d staining was positive in 4/16 cases. Most patients were treated with IVIg and plasmapheresis, others with rapamycin, thymoglobulin, or rituximab. At an average follow-up of 62 months, 8 patients with functioning grafts had a mean serum creatinine of 1.4 mg/dL (122 μmol/L). Antibody-mediated rejection is an important consideration in blood group compatible allograft biopsies with glomerular fibrin thrombi, even with C4d-negative biopsies. However, multidisciplinary evaluation is necessary, given other etiologies, including drug toxicity, hemolytic-uremia syndrome, and large vessel thrombosis. Despite aggressive treatment, both short and long-term graft survival may be compromised.