From Wikipedia, the free encyclopedia. Random glucose test (aka capillary blood glucose) is a blood sugar test taken from a non-fasting subject. This test, also called random blood glucose (RBG) or casual blood glucose (CBG), assumes a recent meal and therefore has higher reference values than the fasting glucose test.his test, also called random blood glucose (RBG) or casual blood glucose (CBG), assumes a recent meal and therefore has higher reference values than the fasting glucose test.