Laboratory diagnosis of clostridium difficile infection. An evaluation of tests for faecal toxin, glutamate dehydrogenase, lactoferrin and toxigenic culture in the diagnostic laboratory.

Faecal samples from 1007 patients suspected of having diarrhoea caused by Clostridium difficile infection are investigated for the presence of toxins A and B and for the presence of C. difficile-specific glutamate dehydrogenase (GDH). Toxigenic culture is performed on all samples and is used as the 'gold standard' for the purpose of the study. A marker for intestinal inflammation, faecal lactoferrin, is used on any samples that give a positive result in any of the above tests. Part of the study also involves an assessment of six commercial toxin kits to detect the presence of C. difficile toxins in faecal samples. This study revealed that the commercial toxin detection kits used can give rise to false-positive and false-negative results and that all demonstrated poor sensitivity when compared to the gold standard of toxigenic culture. Testing of faecal samples for GDH can be useful as a negative screening method as the results of this test show high correlation with culture. Faecal toxin testing can then be performed on all GDH-positive samples (GDH positivity is independent of toxigenicity in strains of C. difficile). The combined use of GDH and toxin testing, coupled with toxigenic culture, revealed that some patients with diarrhoea who harboured toxigenic strains of C. difficile were faecal toxin-negative. Lactoferrin appears to be a useful marker for the presence of inflammatory diarrhoea.