A stool test for Clostridium difficile detects the bacterium or its toxins in a fecal sample to diagnose C. difficile infection. Laboratories typically use toxin assays, GDH screening, and/or PCR for toxin genes. A fresh stool sample is collected in a sterile container; results confirm infection, guide antibiotic treatment, and inform infection‑control measures to prevent spread.

Collect unformed/watery (diarrhoeal) stool specimens—ideally from patients with acute diarrhoea (≥3 loose stools in 24 hours). Do not submit formed stools for C. difficile testing. Obtain a fresh sample promptly, ideally before starting treatment; use rectal swabs only if stool cannot be produced. Label and transport promptly per laboratory instructions to preserve diagnostic accuracy.

Clostridium difficile infection usually produces frequent, watery, foul-smelling diarrhea that can be yellowish or greenish and may contain mucus. Stools are typically loose rather than formed; blood can appear in more severe cases. Color alone doesn’t confirm C. difficile, so testing and clinical assessment are needed if you have persistent, severe, or bloody diarrhea, fever, or abdominal pain.

Clostridioides difficile infection usually causes frequent, watery diarrhea — often profuse, foul-smelling, and sometimes mucoid or bloody. Stools may be watery to liquid, sometimes greenish, with mucus and a strong odor. Severe cases can lead to pseudomembranous colitis with abdominal pain, fever, and leukocytosis; stool testing confirms diagnosis. Dehydration risk is high, requiring prompt medical evaluation.

The preferred stool testing uses a two-step approach: an initial glutamate dehydrogenase (GDH) antigen plus toxin A/B enzyme immunoassay (EIA), with nucleic acid amplification test (NAAT/PCR) used to confirm discordant results or when toxin EIA is negative but clinical suspicion is high. Only test unformed stool from symptomatic patients, since NAAT alone can detect asymptomatic colonization.

Warning signs of C. diff include frequent watery diarrhea (often three or more loose stools per day), severe abdominal pain or cramping, fever, nausea, loss of appetite, and signs of dehydration. Stools may contain blood or mucus. Severe infection can cause intense abdominal tenderness, rapid heart rate, high fever, or symptoms of toxic megacolon and sepsis — seek prompt medical attention if suspected.