“A test that is just a bit too good…”

On one of my rare forays through a research journal I surprised myself by finding a paper that interested me….

Clinical relevance of a positive molecular test in the diagnosis of Clostridium difficile infection. Baker I et al, Journal of Hospital Infection 84 (2013),311-315. Click here for a link to the abstract. Unfortunately the full text requires subscription.

 

Photo accredited to Dr Holdeman
Photo accredited to Dr Holdeman

 

It has long been thought that toxin assays for Clostridium difficile lack sensitivity. This has triggered a move towards PCR or other molecular testing for toxin producing Clostridium difficile strains.

This paper primarily looks at the clinical differences between patient cohorts who are PCR +ve and toxin EIA negative for C.difficile, and patients who are both PCR and toxin EIA positive.

The study showed increased mortality and prolonged duration of diarrhoea in the toxin EIA positive group, compared with the group that was PCR positive but toxin EIA negative. There was no obvious attributable mortality to Clostridium difficile in the group that was PCR positive but toxin EIA negative. (However this seemed to be only on examination of the death certificates as opposed to detailed review of the clinical notes)

The study shows nicely that by using a molecular test such as PCR for C. difficile detection, it may just be a little too good at detecting it, and thus produce positive results that are not clinically relevant (?mostly just colonising). However the study did not specify whether there was any clinical cases suggestive of severe CDAD in the PCR positive, toxin EIA negative group, which would have been nice to know before discounting this cohort altogether.

These findings confirm my clinical suspicions that we have moved to a test which is just a little too good, and that there is probably a continuing need/role for toxin EIA testing in diagnostic algorhythms for disease due to Clostridium difficile.

The only downside of the paper was the declaration of a conflict of interest by one of the authors, although it looks to be fairly minor.

Nice paper. Worth getting hold of and discussing further in your laboratory journal clubs etc.

Michael

p.s. Click here for a previous article on faecal transplantation to treat disease due to Clostridium difficile.

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