Practical reasons for poor RDT performance

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Practical considerations Bibilography: [1] 1. Selection and procurement of MDTs (a) Quality of test design/production. There may be significant variation of performance between tests, users are advised to check test performance (see WHO testing information available from [2]. (b) Lot variability. Variability between different production batches has been observed and should be considered if RDT performance is less than expected. 2. Stability and storage issues (a) RDTs typically have a shelf-life of 18–24 months providing storage is appropriateR. (b) Tests can suffer degradation if stored in inappropriate heat or humidity: generally tests are stable in the range 2–30°C or higher, but these limits may be exceeded in many countries, and continuous product refrigeration to the point of use may not be guarenteed in developing countries. 3. Operator training (a)Problems in test usage may include inappropriate placement of test reagents or blood sample. Poor interpretion of faint lines. Inadequate training or reference materials In the case of malarial RDTs, the WHO requires a panel detection score of 75% at a parasitaemia of 200 parasites/μl in order for the product to warrant endorsement. [16] However, the threshold for pyrogenic onset has been shown to vary from 10 to 200,000 parasites/μl, with 22% of patients developing their first acute fever at a parasite load below 200/μl. [75] Thus, even for the select assortment of commercial malaria RDTs demonstrating compliance with WHO standards, sufficiently low limits of detection have not been demonstrated for the early and accurate diagnosis of nascent infections, or of asymptomatic carriers. In order to improve test sensitivities when dealing with non-ideal biomarkers, manufacturers of RDTs often seek to use the multiplexed detection of distinct, species-specific antigens. In the case of malaria, RDTs are often multiplexed to detect HRP2 and the P. vivax variant of parasite lactate dehydrogenase (Pv-pLDH), to distinguish between infections by P. falciparum and P. vivax. Alternatively, tests can be multiplexed to select for Pf-pLDH and HRP2, which yields highly sensitive indications for falciparum malaria. [16] Multiplexed RDTs have also proven to be efficacious in discriminating between distinct diseases with non-specific symptomatic presentations.