Comparison of Three Screening Test Kits for G6PD Enzyme Deficiency: Implications for Its Use in the Radical Cure of Vivax Malaria in Remote and Resource-Poor Areas in the Philippines

Abstract

Objective: We evaluated a battery of Glucose-6-Phosphate Dehydrogenase diagnostic point-of-care tests (PoC) to assess the most suitable product in terms of performance and operational characteristics for remote areas.

Methods: Samples were collected in Puerto Princesa City, Palawan, Philippines and tested for G6PD deficiency with a fluorescent spot test (FST; Procedure 203, Trinity Biotech, Ireland), the semiquantitative WST8/1-methoxy PMS (WST; Dojindo, Japan) and the Carestart G6PD Rapid Diagnostic Test (CSG; AccessBio, USA). Results were compared to spectrophotometry (Procedure 345, Trinity Biotech, Ireland). Sensitivity and specificity were calculated for each test with cut-off activities of 10%, 20%, 30% and 60% of the adjusted male median.

Results: The adjusted male median was 270.5 IU/10(12) RBC. FST and WST were tested on 621 capillary blood samples, the CSG was tested on venous and capillary blood on 302 samples. At 30% G6PD activity, sensitivity for the FST was between 87.7% (95%CI: 76.8% to 93.9%) and 96.5% (95%CI: 87.9% to 99.5%) depending on definition of intermediate results; the WST was 84.2% (95%CI: 72.1% to 92.5%); and the CSG was between 68.8% (95%CI: 41.3% to 89.0%) and 93.8% (95%CI: 69.8% to 99.8%) when the test was performed on capillary or venous blood respectively. Sensitivity of FST and CSG (tested with venous blood) were comparable (p>0.05). The analysis of venous blood samples by the CSG yielded significantly higher results than FST and CSG performed on capillary blood (p<0.05). Sensitivity of the CSG varied depending on source of blood used (p<0.05).

Conclusion: The operational characteristics of the CSG were superior to all other test formats. Performance and operational characteristics of the CSG performed on venous blood suggest the test to be a good alternative to the FST.

Fig 1. Distribution of G6PD activity among the study population.

(A) G6PD activity among male students. (B) G6PD activity among female students. Legend: Red line indicates 100% G6PD activity (the adjusted male median)

Fig 2. Distribution of the qualitative test results of study participants by G6PD activity Legend: Results are presented per test performed.

Red circles indicate a G6PD deficient result, black circles indicate a G6PD normal result, horizontal lines indicate G6PD activity at 10%, 20%, 30%, 60% and 100% G6PD activity. CSGven = Carestart G6PD RDT from venous sample, CSGcap = Carestart G6PD RDT from capillary sample, FSTdefint = Fluorescent spot test considering intermediate results as G6PD deficient, FSTdef = Fluorescent spot test considering intermediate results as G6PD normal, WST = WST 8/1 PMS methoxy test