Hyperacute rejection occurs rarely since screening of recipient for anti-donor antibodies has been introduced. However, the focal or diffuse acute cellular rejection is more common and is diagnosed by EMB. The degree or severity of rejections is graded on a scale from 0 to 4 with a grade 3 or more being considered severe. Most acute cellular rejections occur within the first year after transplant. Chronic rejection or allograft arteriopathy occurs later and is monitored by coronary angiography.