Literature review > Issue 1 > Review Barenfanger et al. 

The article addresses the problem of whether it is essential to inoculate the bottom pouch of the InPouch TV test if the top pouch cannot be read immediately or whether it is possible to delay inoculation of the bottom pouch, beyond the 15 minutes suggested by the manufacturers, until the top pouch has been read. This information could be useful for busy clinics when it is not possible to read wet preparations immediately.

The study has a relatively simple design but, unfortunately, the authors were not able to comply with the originally proposed 'blind' reading of the pouches by two technologists and most were read by only one technologist with no quality control reading. This introduces an area of bias into the results.

The investigation was on symptomatic women. This population would have a higher prevalence and hence a greater chance of TV isolation to validate the methods used. However, the methods used to inoculate the InPouch tests are not made clear. The authors state that vaginal secretions were suspended in a few millilitres of saline and this was used for a standard wet preparation and for inoculation of the InPouch. The authors do not say how secretions were obtained or what constitutes a few millilitres and how much and by what means this was inoculated into the InPouch. It is far more usual and efficient to directly inoculate the InPouch with a vaginal swab. The method here means diluting possible trichomonads first in saline and then in Inpouch media, this dilution may help to account for why 5 more samples were positive from the traditional wet preparation than from the top of the InPouch. We then assume that wet preparations, from the initial saline suspension and the top pouches, were read after the same time delay for direct comparison.

For direct examination, regardless of time, the traditional wet preparation was more sensitive than using either pouch of the InPouch, whereas the InPouch was able to detect more positives after incubation and growth. This would be expected and is the major advantage of its use. There was no difference between the positives detected in the pouches that had been inoculated immediately than in those that had a delayed inoculation of up to three hours. This is the major finding of the paper and the usefulness of this is what we need to consider.

A point of note is that in this study, InPouch tests were discarded if positive after reading the top pouch. This would also be the case if they were to be used instead of traditional wet preparations. This would not be a cost effective approach to resources, as the cost of an InPouch is around 20 times higher than that of a traditional wet preparation. A more cost effective approach would be to use the traditional wet preparation, which in this study was more sensitive, and to inoculate an InPouch if this was negative, however, this would again have some time implications if not done immediately. Alternatively if a direct result is not essential for patient management, routine inoculation and incubation in the InPouch would be the most sensitive Trichomonas vaginalis detection system.

The authors conclude they will in future switch from using traditional wet preparations to the InPouch system. They feel that the extra costs are justified by accommodating transit delays and the increased sensitivity of culture. For many laboratories, particularly in smaller health centres or developing countries, this has both logistical problems, in terms of extra equipment, staff time and procurement of InPouches, and importantly, the extra cost implications may not be acceptable. All these factors need to be part of the equation when deciding to adopt a new test.

The ability to delay inoculating the bottom of an InPouch in order to microscopically read the top pouch, would be particularly relevant in a busy clinic or in a field trial, or where no microscopy is available on site. InPouch tests are very useful in these situations as well as more sensitive in detection of low numbers of TV, such as in male urethritis cases. It is a very useful tool in STI diagnosis and seemingly more forgiving and adaptable than specified.

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