Thick film analysis for xRapid is now functional.
In its current form we have matched the accuracy of standard rapid diagnostic tests based on slides from the London School of Hygiene and Tropical Medicine. Like our thin film analysis, our diagnostic test based on a thick film slide is still a fraction of the cost of RDTs and provides a faster, cheaper and more accurate method of diagnosis than anything on the market.
The analysis of thick film slides using xRapid gives an accurate range of parasite count. The technology is able to tell if the patient has high, medium or low parasitaemia. Quantitative as well as qualitative diagnosis such as this is an important factor in why xRapid gives a superior diagnosis to other methods. Currently, our thick film analysis is unable to show the specific plasmodium species present in the blood, but our thin film analysis can achieve this to a very high level of accuracy.
We have been working on introducing thick film analysis for a while but recent trials and conversations with potential users have shown that it is very much needed both in the field and in the laboratory. Our users in Uganda and Benin have effectively demanded it. The reasons are that thick films are easier to prepare than the thin films, and the concentration of parasites is much higher thereby providing a lower limit of detection. The current method of staining a thick film slide is mainly easier because a user doesn’t have to carry two fluids. The minimum a user needs to treat a slide is purified water and giemsa. This simplifies the preparation as the third fluid for a thin film analysis – methanol – is not required.
However, the thick film does have its issues when compared to the thin film. There is often a degree of human error in preparing a thick film slide meaning that it is often not easily readable with the eye. This is why some people need a lot of training. Most of the training for diagnosing malaria should really be spent on how to prepare the slide rather than reading it because ensuring a high level of quality in how the slide is prepared is so vital for good results.
It is still important to note that preparing the thick film with three fluids is better practise than two. With the thin film you fix using methanol and the thick film needs the lysis of the red blood cells. At the Pitié-Salpétrèere Hospital in Paris a saponin solution is used for the lysis of red blood cells and platelets on a thick film slide, which produces better results and despite the use of an extra fluid alongside purified water and giemsa stain, provides a much easier to read slide. The new xRapid thick film analysis enables to read slides whose preparation was beyond optimal.
Because of the complexities of slide preparation we will be shipping all units of xRapid with instructions for best practice in this area alongside our instructions for using the software and hardware.