When would you consider a workup for C. diff in a patient with diarrhea under-going concurrent chemoradiotherapy for rectal cancer?  

Good question – and hard to pinpoint a strict answer. I think any time the diarrhea is out of proportion to expectation (i.e., very early in RT course), clinically significant (dehydration, etc), and not controlled or responding to anti-diarrheal medications, especially in the setting of C. di...