Enhanced Diagnosis of Chronic Antibody-mediated Rejection Using Peritubular Capillary Multilayering

Background. Peritubular capillary multilayering (PTCML) of basement membranes is an ultrastructural feature of chronic antibody-mediated rejection (AMR) with uncertain diagnostic thresholds. Methods. This single-center, prospective cohort study evaluated the relationships of PTCML with chronic AMR in 2541 kidney samples from 1195 recipients. Results. Epidemiological modeling found that younger recipients, living donation, early AMR, pulse corticosteroid rejection treatment, later presentation, and higher donor-specific antibody strength were clinical risk factors for an abnormal PTCML score of ≥3. The total number of PTC layers was correlated with posttransplant time, AMR histology, donor-specific antibody positivity, renal dysfunction, proteinuria, and graft failure. Histological Banff cg, ptc, C4d ptc , and C4d glom independently predicted PTCML ≥3. Mild PTCML of 3–4 layers with circumferential remodeling in multiple PTC showed 82.9% sensitivity and 72.7% specificity against the Banff cg≥1a reference test, verified using Banff 2022 AMR criteria, and considered “suspicious” for chronic AMR. PTCML ≥5 correlated with late graft failure. Normal PTC (n = 322) in early protocol samples showed 1 basement membrane layer, except for 12.5% with mild segmental reduplication involving 13.7 ± 10.2% capillary circumference. Circumferential scoring efficiently separated mild segmental PTCML from normal variability against pathological AMR multilayering. The poor 30.0% sensitivity and 91.1% specificity (n = 374 late indication biopsies, 2029 PTCs) of the Banff 2013 AMR criteria improved to 55.0% and 89.7% using modified PTCML ≥7 or 2×PTCML ≥5 criteria, which allowed for a diagnostic disease “rule-in.” Conclusions. Circumferential multilayering from PTCML ≥3 replicated across multiple capillaries optimally recognized mild chronic AMR as a superior histological marker of chronic tissue injury with high sensitivity. These ultrastructural diagnostic criteria for the detection of early chronic AMR phenotypes require multicenter validation.