Accuracy of raepid tests as compared with field microscopy, for diagnosis of Malaria in adolescents and adult patients in Mulago Hospital
Luzige, Ssekiganda Simon
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Background: Blood smear microscopy is the recommended gold standard test for laboratory confirmation of malaria. However, due to some limitations associated with microscopy such as being labor intensive and time consuming, rapid diagnostic tests (RDTs) are becoming attractive alternatives to microscopy because these tests are fast, easy to perform, and do not require electricity or specific equipment. Although their accuracy in a number populations and epidemiological settings has been reviewed, the results are often variable and not easily transferable. This study was therefore performed to evaluate the accuracy of RDTs for the diagnosis of malaria in adolescents and adult patients in Mulago hospital. Methods: From February to May 2007, we evaluated the accuracy of SD malaria pLDH P flPan. SD malaria HRP-ll Pi Paracheck and PI Parabank as compared to field microscopy of blood smears in five hundred fifty five (555) adolescent and adult patients clinically suspected to have malaria at Mulago hospital. With microscopy as the gold standard, we analyzed for the accuracy of each RDT by computing for sensitivity, specificity, positive and negative predictive values as well as positive and negative diagnostic likelihood ratios (DLRs). Results: The adjusted prevalence of smear confirmed malaria was 20% (111 patients). SD malaria pLDH P flPan and Paracheck had similar sensitivities (89%) meanwhile; SD Bioline-Pf HRP2 and Parabank were respectively 87% and 83%. Overall the greater the parasite density the higher was the sensitivity. The pLDH based RDTs SD malaria pLDH Pf/Pan and Parabank had a higher specificity (96%) than the HRP2 based tests SD malaria HRP-11 P f(88%) and Paracheck (91%). The positive predictive values of SD malaria pLDH P jlPan and Parabank were respectively 84 and 87 compared to HRP2 based tests SD malaria HRP-II P.f(64%) and Paracheck (70%). However, the negative predictive values were similar for all tests (96%-97%). Also, the positive diagnostic likelihood ratios for SD malaria pLDH P jlPan, Parabank, SD malaria HRP-II P.f and Paracheck were respectively 21, 23, 7 and 9 whereas the negative diagnostic likelihood ratios was 0.1 for all RDTs. Conclusions: The accuracy of rapid tests (SD malaria pLDH Pf/Pan, Paracheck, 3D Bioline-P .fHRP2 and Parabank) is comparable to blood smear microscopy in the diagnosis of malaria in adolescents and adult patients in Mulago hospital. Rapid diagnostic tests (RDTs) should be considered as alterative methods for supporting or ruling out malaria in adolescents and adult patients suspected to have malaria in Mulago hospital.