non-blanching rash non-blanching rash a non-blanching rash (nbr) is a skin rash that does not fade when pressed with, and viewed through, a glass. non-blanching rashboth petechiae and purpura on the lower limb due to medication induced vasculitisspecialtydermatology, hematology it is a characteristic of both purpuric and petechial rashes. individual purpura measure 3–10 mm (0.3–1 cm, 3⁄32-3⁄8 in), whereas petechiae measure less than 3 mm. a non-blanching rash can be a symptom of bacterial meningitis, but this is not the exclusive cause.