newucpat, I think the test for c. diff. is a stool sample. I think you should ask your husband's GI to order one since it wasn't done before.
I do think the symptoms for UC and c. diff. are similar b/c when my flare became a lot worse a couple weeks ago, the first thing my GI did was order a stool sample to check for infections.
Female, Age 19, Dx w/ UC August 2007
1000 mg Canasa, Proctofoam, Rifaximin 2/day
Digestive Advantage (Crohn's & Colitis) 3 pills/day, 1 Florastor/day