Reactivity of Blood Samples Spotted onto Filter Papers in the WST-8 Method for Screening of G6PD Deficiency.

Deficiency of glucose-6-phosphate dehydrogenase (G6PD) causes acute hemolytic anemia triggered by oxidative drugs such as primaquine. It is therefore essential in malaria-endemic areas for malaria patients to be confirmed for their G6PD activity before taking primaquine. The WST-8 method, a newly established screening method for G6PD deficiency, has been demonstrated to be suitable for field conditions, particularly for on-site malaria surveys. Here we report a laboratory evaluation by this method of the reactivity of blood-spotted filters. A time-course experiment was conducted to evaluate the reactivity of blood samples spotted onto 4 types of filter paper, Whatman 31ET Chr (ET), 3MM Chr (3MM), P81, and Advantec No. 2 (AD2). The rank of the relative reaction intensity was ET > 3MM = AD2 > P81. Blood-spotted filters stored at 4 degrees centigrade gradually decreased G6PD reactivity with the passage of storage time, whereas those stored at room temperature rapidly reduced their reactivity. Unexpectedly, saponin supplementation reduced the reactivity of blood-spotted filters. In conclusion, 1) ET is the most suitable filter for the WST-8 method ; 2) blood-spotted filters stored in cold condition can be assayed within 14 days, or those stored at room temperature should be tested within 3 days ; and 3) reaction mixtures should not contain saponin.