Perhaps it also depends on what kind of specimen tube you are using. When I did my clinicals, the blood bank there would use the long pink tops with EDTA. In my four weeks there, I saw rouleaux 10 times. However this was a city of 200,000 people. When I got my first job at a different hospital, the blood bank there was still using red tops. Out of the whole year, I saw only two patients with rouleaux. But this is a city of only 99,000 people.