Figure 19. Banff Additional Diagnostic Parameter ptcml (peritubular capillary basement membrane multilayering) is only demonstrable by EM. A, This Additional Diagnostic Parameter is a criterion for AMR chronicity. It is defined as 7 or more layers of basement membrane in at least a single cortical peritubular capillary and 5 or more in at least 2 additional capillaries. This particular capillary shows 8 layers (arrow). Transmission EM, original magnification x14,000. B, this image demonstrates a peritubular capillary with 5 layers of basement membrane (arrow). Transmission EM, original magnification x10,000.