An assessment of various blood collection and transfer methods used for malaria rapid diagnostic tests

Abstract

Background: Four blood collection and transfer devices commonly used for malaria rapid diagnostic tests (RDTs) were assessed for their consistency, accuracy and ease of use in the hands of laboratory technicians and village health workers.

Methods: Laboratory technicians and village health workers collected blood from a finger prick using each device in random order, and deposited the blood either on filter paper or into a suitable casette-type RDT. Consistency and accuracy of volume delivered was determined by comparing the measurements of the resulting blood spots/heights with the measurements of laboratory-prepared pipetted standard volumes. The effect of varying blood volumes on RDT sensitivity and ease of use was also observed.

Results: There was high variability in blood volume collected by the devices, with the straw and the loop, the most preferred devices, usually transferring volumes greater than intended, while the glass capillary tube and the plastic pipette transferring less volume than intended or none at all. Varying the blood volume delivered to RDTs indicated that this variation is critical to RDT sensitivity only when the transferred volume is very low.

Conclusion: None of the blood transfer devices assessed performed consistently well. Adequate training on their use is clearly necessary, with more development efforts for improved designs to be used by remote health workers, in mind.

Figure 1

Blood collection and transfer devices. The plastic straw and plastic loop collect a film of blood by touching the finger prick; the glass tube collects blood by capillary action, while the plastic pipette aspirates blood similar to a conventional dropper.

Figure 2

Test band intensity of various RDTs using different blood volume and parasitaemia. At 200 parasites/μL blood, using less blood than the required volume did not give clearly visible test bands (less than 1 on the RDT rating chart). At 2000 parasites/μL blood, all RDTs gave visible test bands (1 or higher) in all the blood volumes used. Note that Optimal is designed to use 10 μL of blood, the other tests 5 μL.