Sample Paper on Rapid Diagnostic Tests for Early Diagnosis of Malaria

Rapid Diagnostic Tests for Early Diagnosis of Malaria

Results

In detecting Plasmodium vivax and Plasmodium falciparum infections, the OptiMal Pf/Pan Test achieved sensitivity and specificity of more than 90%. The ICT Pf/Pan Test was comparable in terms of specificity (>92%); in terms of sensitivity, though, it was 72-79%.

Performance of the OptiMal Pf/Pan Test was investigated in 370 blood samples. The tests were worked on over four months. Kits were maintained at room temperature in different health centers located in Mumbai, India. The kits incorporated P. falciparum (n=220), P.vivax (n=80), P. ovale (n=50) and P. malariae (n=20). Generally, the sensitivity for the discovery of Plasmodium. falciparum occurred at 88.9%, increasing to 94.8% and 99.4% at parasitic concentration beyond 100 and 1,000/microl accordingly. Results indicated the sensitivities for the three plasmodium parasites as 77.5% (P.vivax), 18.6% (P.ovale) and 28.9% (P.malariae). Moreover, the sensitivity of P.vivax stretched to 91.6% for parasite densities greater than 450/microl. Erroneous identification of species occurred in 12/370 samples (3.2%), including 9/310 (2.9%) P. falciparum samples initiated the appearance of pan-pLDH stroke. “The agreement from different researchers was harmonious at kappa values>0.82, agreeable on both approving and disapproving side making the results satisfying (Hawileh, R. A., E. I. Saqan, and J. A. Abdalla 291).

Kim, Saorin et al conducted a similar experiment where RDT results were weighed against thick blood smear (TBS) results to establish the level of sensitivity, specificity, and accuracy of the RDT (243). The sensitivities of the OptiMal Pf/Pan test were 79.9% Plasmodium flaciparum malaria diagnosis and 86.7% for non-P. falciparum infectivity. The outcome indicated a solid agreement of 87.2% for P. falciparum, and 87.5% for non-P.falciparum infections (Kappa index=0.75 and 0.76, respectively).  The correlation between the ICT Pan test and TBS was 92.3 % for P.falciparum and 81.3% for non-P.falciparum infection. The Kappa index was 0.82 and 0.58 for the closing analysis of P. falciparum and non-P.falciparum, correspondingly.

 

Malarial parasite Microscopy +ve (%) QDx Rapid +ve (%)
P. falciparum 220 (59%) 198 (70.7%)
P.vivax 80(21.6%) 47(16.8%)
P.malariae 20(5.4%) 25(9%)
P.ovale 50(13.5%) 10(3.5%)
Total 370 280 (75.7%)

 

Using the QDx Malaria Rapid test, 280 (75.7%) of the 370 blood samples were positive for malaria. 198 (70.7%) of these were positive for p.falciparum, 47(16.8%) were positive for P.vivax species and 25(9%) approving for P.malariae, and 10(3.5%) were positive for P.ovale.

Discussions

Devices to detect aldolase (used for the pan-specific line in a variety of products) have the highest lower limit of detection. i.e., lower sensitivity at low parasitemias. The commonality of all tests is that low parasitemias (<500 parasites/µL), common in patients with malaria, produce a much lower sensitivity and are inferior to microscopic diagnosis. The pan-specific line for pLDH-based RDTs has lower sensitivity for detecting Plasmodium ovale and Plasmodium malariae infections than it does for P.vivax.

pLDH-based RDTs  are usually two component systems comprising of a conjugate well and a test membrane dipstick and is based on the principle of immunochromatography. “The conjugate well contains an indicator-tagged monoclonal antibody to PLDH, dried onto its surface” (Jang, Jin et al 180-181). The anti- pLDH antibody is specific to all isoenzymes LDH of the genus plasmodium.

Sample of blood is put in conjugate wells along with the lysing buffer. pLDH if present in the sample reacts with the anti-pLDH conjugate in the well and rises up the membrane dipstick where it is captured by anti-Pf, specific pLDH and anti-pan specific pLDH, causing the appearance of a colored band at the respective regions. Absence of bands at this position is an indication of a negative test result. The unreacted conjugate reacts with the antimouse antibodies at the control region and serves to validate the test performance. “QDx Rapid for malaria employs exclusive antibodies that defect malaria antigens in the blood of infected individuals”(Shedid, Marwan T., and Wael 140-141).

RDTs use small blood samples obtained by finger prick or by venepunture and employ a “lateral diffusion” system similar to a pregnancy test to generate results. RDTs display results of visible “bands” that can be interpreted by non-experts users with limited facilities. Generally, a blood specimen to be tested (2-50 µl) is lysed in buffer solution containing one or more malaria-specific ‘detection antibodies.’ The detection antibody is coupled to a visually observable label. Where specific antigen is present, a complex is formed between that antigen and its cognate labeled antibody.  The labeled antigen-antibody complex generated is then bound by a second ‘capture-antibody’ that recognizes the same antigen, and which is immobilized as a line on the test strip. “A positive outcome generates a visible line of antigen-antibody complex” (Lee, Sook Young et al 419). A separate immobilized capture antibody recognizes the labeled detection antibody alone; this control band will produce a line in the absence of malaria antigen and confirms that the test has been performed correctly and the results can be interpreted.

In terms of diagnostic sensitivity, WHO requires RDTs to reliably detect infections of 100 parasites per microlitre of blood (95% sensitivity). This is equivalent to the diagnostic sensitivity reasonably expected of a filed microscopist diagnosing malaria in endermic regions. Sensitivity becomes less reliable below 100 parasites per microlitre, and this contrasts with the ‘gold standard’ sensitivity achieved by an expert microscopist in good conditions, who should detect 5-10 parasites per microlitre. Sensitivity commonly is dependent on the species. For P.falciparum parasites, RDT sensitivity frequently exceeds 100 parasites per microlitre, although genetic variations of P. falciparum antigens may diminish sensitivity in some cases. For other malarial species, sensitivity of detection is recognized to be less good, particularly in Plasmodium.ovale as well as Plasmodium.malariae where both QDx Rapid and RTDs may fail to identify infections that are clinically substantial.

 

 

Works Cited

Hawileh, R. A., E. I. Saqan, and J. A. Abdalla. ‘Simplified Optimum Design Procedure For Special Unbonded Posttensioned Split Precast Shear Walls’. Journal of Structural Engineering 139.2 (2013): 294-299.

Jang, Jin et al. ‘Pldh Level of Clinically Isolated Plasmodium Vivax And Detection Limit Of Pldh Based Malaria Rapid Diagnostic Test’. Malar J 12.1 (2013): 181

Kim, Saorin et al. ‘Malaria Rapid Diagnostic Test As Point-Of-Care Test: Study Protocol For Evaluating The VIKIA® Malaria Ag Pf/Pan’. Malar J 14.1 (2015).

Lee, Sook Young et al. ‘Comparisons of Latex Agglutination, Immunochromatography And Enzyme Immunoassay Methods For The Detection Of Rotavirus Antigen’. The Korean Journal of Laboratory Medicine 27.6 (2007): 437.

Shedid, Marwan T., and Wael W. El-Dakhakhni. ‘Plastic Hinge Model and Displacement-Based Seismic Design Parameter Quantifications for Reinforced Concrete Block Structural Walls’. Journal of Structural Engineering 140.4 (2014): 04013090.