The Clostridium Difficile Toxin/Gdh W/Refl To PCR test. After treatment with antibiotics, many patients develop gastrointestinal problems ranging from mild diarrhea to severe pseudomembranous colitis. This organism is an opportunistic anaerobic bacterium that grows in the intestine once the normal flora has been altered by the antibiotic. If the GDH Antigen is detected and the Toxin A and B are not detected or the GDH Antigen is not detected and the Toxin A and B are detected, Clostridium difficile Toxin B, Qualitative, Real-Time PCR will be performed at an additional charge.