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Practical reasons for poor RDT performance: Difference between revisions

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|colspan="1" style = "font-size:100%; color:black; background: FFFAFA"|<span style="color:navy>'''The value of RDT compared with microscopy: thick blood films'''</span>
|colspan="1" style = "font-size:100%; color:blasck; background: FFFAFA"|<span style="color:navy>'''Practical considerations '''</span>


see also: [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4652944/]
<span style="font-size:90%">Bibilography: [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4652944/], [https://www.who.int/teams/global-malaria-programme/case-management/diagnosis/rapid-diagnostic-tests]</span>


'''Selection and procurement of MDTs'''</br>
1. Quality of test design/production. There is significant variation of performance between tests, users are advised to check test performance (see WHO testing information available from [https://www.who.int/teams/global-malaria-programme/case-management/diagnosis/rapid-diagnostic-tests].</br>
2. Lot to lot variability. Variability between batches has been observed and should be considered if RDT performance is less than expected.</br>


<span style="font-size:90%">'''1. Selection and procurement of MDTs'''</br>


'''2. Heat stability of the RDT test''' storage</b>
<span style="font-size:90%">(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 ref 2 above)</br>(b) Lot variability. Variability between different production batches has been observed and should be considered if RDT performance is less than expected.</br>
potential for degradation due to heat and humidity. Extended exposure to these conditions can drastically reduce the shelf life of RDTsRDT manufacturers recommend continuous product refrigeration, from the point of manufacture all the way to rural clinics and the point of use. However, in many developing countries, cold-chain continuity cannot be guaranteed. WHO analysis of commercially available malaria RDTs found that 37 out of 50 tests claimed stability ranges of 2–30°C, and that the remaining 13 tests claimed stability up to 40°C. [18] However, in many countries, ambient temperatures regularly exceed these limits.
'''3. Age of test/reagents'''</br>
Operator-Specific Factors
Operator-Inappropriate placement of reagent or blood drop
Operator-Interpreting faint lineBy virtue of being targeted for use at the point-of-care, immunochromatographic RDTs must be amenable to facile and accurate interpretation by minimally trained operators. However, test lines are often subject to highly variable and user-dependent readings, which can be impacted by user biases, low signal contrast, and inadequate training 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.
<span style="font-size:90%">'''2. Stability and storage issues'''</br>


<span style="font-size:90%">(a) RDTs typically have a shelf-life of 18–24 months providing storage is appropriateR.</br>(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.


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.  
<span style="font-size:90%">'''3. Operator training'''</br>


RDTs typically have a shelf-life of 18–24 months, allowing sufficient time for delivery, distribution, and use in most settings.
<span style="font-size:90%">(a)Problems in test usage may include inappropriate placement of test reagents or blood sample on RDT.</br>(b)Poor interpretion of faint lines.</br>(c) Inadequate training or reference materials

Latest revision as of 16:05, 6 October 2024

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Practical considerations

Bibilography: [1], [2]


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 ref 2 above)
(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 on RDT.
(b)Poor interpretion of faint lines.
(c) Inadequate training or reference materials

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