Maria is a 22 year old law student and attends the GP surgery distressed about a 2 month history of intermittent bloody diarrhoea and abdominal pain. There is no history of travel, weight loss or any fevers. She is finding it very embarrassing to frequently leave lectures as her stool frequency can be several times a day. There is no relevant family history.
Based on the likely diagnosis, which faecal investigation would be most diagnostic?