Enzyme Deficiency Diagnosed with Rapid Tests
By Labmedica International staff writers
Posted on 07 Jun 2017
Image: The Care-Start G6PD RDT rapid test (Photo courtesy of Access Bio).
Glucose-6-phosphate dehydrogenase (G6PD) is a rate-limiting enzyme of the pentose phosphate pathway and is closely associated with the hemolytic disorders among patients receiving anti-malarial drugs, such as primaquine.
G6PD deficiency (G6PDd) is an impending factor for radical treatment of malaria, which affects the clearance of gametocytes from the blood and subsequent delay in the achievement of malaria elimination. About 8% of the people who are exposed to malaria have an inherited disorder that impairs G6PD, leaving them vulnerable to develop clinical consequences.
Scientists at the World Health Organization regional office conducted a cross-sectional prevalence study during from April to December 2013. Volunteers who were between five and 60 years, without known chronic diseases, and consenting/assenting for voluntary participation were enrolled for the study. Equal proportions of equal to or more than 200 participants from each of six malaria endemic district were enrolled considering ethnic and demographic representation of the population groups.
Whole blood specimens from the1,341 enrolled volunteer participants were collected and tested immediately using Care-Start G6PD RDT and BinaxNOW G6PD test kits in the field settings. The Care-Start RDT format is a qualitative enzyme chromatographic test, based on the reduction of colorless nitroblue tetrazolium dye to dark colored formazan. Samples with normal G6PD activity produced a distinct purple color in the result window, while no color change was observed for samples with G6PDd subjects. The BinaxNOWG6PD test is a qualitative enzyme chromatographic test (ECT) for detecting G6PD activity. The test device contains a lateral flow test strip comprised of a white sample pad and a reaction pad. When no change in the red color of the sample front was observed at the test read time, the sample was presumed to be deficient in G6PD enzyme activity.
The team reported that out of total 1,341 blood specimens collected from six districts, the overall prevalence of G6PDd was 97/1,341 (7.23%) on BinaxNOW and 81/1,341 (6.0%) on the Care Start test. A higher prevalence was observed in male than females; male 10.2% versus female 5.4% with BinaxNOW. G6PDd was higher in two ethnic groups and two districts. The authors noted that Care-Start kits were designed for one step, with all available peripherals, while BinaxNOW had multiple steps, which included the additional step of sample mixing with buffer in the supplied tube. The result window of Care-Start test was clearly visible with distinct purple color appearance for normal cases and transparent (white background) in G6PD deficient cases.
The authors concluded that the prevalence of G6PD deficiency in Nepalese population varies in ethnic groups, strongly recommending need of G6PDd testing before the start of primaquine for each confirmed Plasmodium vivax case. Knowing the G6PDd status gives leverage to use 14 days primaquine in G6PD normal patients, while weekly primaquine under close clinical monitoring/medical supervision with ready access to blood transfusion services in G6PD deficient cases. The study was published on May 23, 2017, in the Malaria Journal.