An International Survey of Glucose-6-Phosphate Dehydrogenase Laboratory Reporting Practices: Implications for Tafenoquine Eligibility Assessment

Abstract

Context.— Glucose-6-phosphate dehydrogenase (G6PD) activity is used in the evaluation of hemolysis risk in patients being assessed for G6PD deficiency. A long-acting 8-aminoquinoline drug (tafenoquine) used in malaria treatment is contraindicated in patients with G6PD deficiency (<70% normal G6PD activity). The current state of G6PD reporting practices to support clinical eligibility assessment is poorly understood. Objective.— To assess clinical laboratory reporting practices for G6PD testing. Design.— In October 2019 and October 2020, voluntary questionnaires were distributed to 327 and 324 laboratories participating in the College of American Pathologists G6PD proficiency testing (PT). Results.— Two hundred fifty-seven and 119 laboratories responded to the 2019 and 2020 questionnaires, respectively. Few laboratories have received clinical questions about average normal G6PD activity (US/Canada, 2.0% [3 of 149]; international, 8.4% [9 of 107]), whereas slightly more have determined the average normal G6PD activity for their own assay and patient populations (US/Canada, 6.7% [10 of 149]; international, 19.4% [21 of 108]). Few laboratories report G6PD activity in percent of normal format (US/Canada, 2.7% [4 of 149]; international, 8.3% [9 of 108]). The most common unit of measurement in use for quantitative G6PD reporting is unit per gram of hemoglobin. Reference intervals vary based on assay, reaction temperature, and participant laboratory and demonstrate moderate correlation (r = .46–.51) to G6PD activity measured from a “normal” PT challenge specimen. Nearly half of participants (47.8% [85 of 178]) categorized a quantitatively “intermediate” G6PD PT challenge as “normal” when using qualitative assays. Conclusions.— Percent of normal G6PD activity reporting would facilitate patient eligibility assessment for drugs, such as tafenoquine. Quantitative assays are better able to differentiate “intermediate” specimens than qualitative assays.