RDT Quiz A Q5

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RDT Quiz A Q5 RDT tests use specific antibodies to identify the malaria species. Users often believe that it is not important to know which antibodies their own test uses. However, different antibodies are known to have particular strengths and weaknesses. Image from section "How RDT tests work" RDT tests that use antibodies that detect the malarial antigen HRP2 are widely used. Which of the statements below are true of HRP2 (select all that apply)? The antigen identifies only P.falciparum The antigen identifies P.vivax HRP2 gene-deletion may affect results Antibodies to pfLDH are more sensitive May be negative in severe infection Explanation of correct answer (click "Expand"). Short answer taken from section "RDT test antigens" (see the section for full details and links). P.falciparum parasites produce “histidine-rich” proteins (HRP). The HRP2 antigen is highly expressed and stable, and is useful in the detection of P.falciparum infection only. At a high parasitaemia the sensitivity of HRP2 (like LDH-based tests) is likely to exceed 90% detection for P.falciparum. At lower parasite levels (<1000 parasites/μL) the sensitivity will be significantly less but HP2-based assays may perform better than LDH-based assays in these circumstances. HRP2 may be affected by false negative results when malaria antigen levels are very high (the prozone-like or postzone phenomenon (for full description in the RDT-interpretation sections). HRP2 gene is increasingly subject to gene deletion in some geographical areas* which may cause false negative results (see sections on RDT interpretation).

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