Date Published: January 22, 2019
Publisher: The American Society of Tropical Medicine and Hygiene
Author(s): Sampa Pal, Pooja Bansil, Germana Bancone, Sevan Hrutkay, Maria Kahn, Gornpan Gornsawun, Pimsupah Penpitchaporn, Cindy S. Chu, François Nosten, Gonzalo J. Domingo.
Glucose-6-phosphate dehydrogenase (G6PD) deficiency, a common genetic blood condition, can result in kernicterus at birth, and later in life as severe hemolysis on exposure to certain infections, foods, and drugs. The unavailability of point-of-care tests for G6PD deficiency is a barrier to routine curative treatment of Plasmodium vivax malaria with 8-aminoquinolines, such as primaquine. Two quantitative reference tests (Trinity Biotech, Bray, Ireland and Pointe Scientific, Canton, MI; Cat No. G7583) and the point-of-care STANDARD™ G6PD test (SD Biosensor, Suwon, South Korea) were evaluated. The STANDARD G6PD test was evaluated at multiple temperatures, in anticoagulated venous and capillary samples, including 79 G6PD-deficient and 66 intermediate samples and across two laboratories, one in the United States and one in Thailand. The STANDARD test performed equivalently to a reference assay for its ability to diagnose G6PD deficiency (< 30% normal) with a sensitivity of 100% (0.95 confidence interval [CI]: 95.7–100) and specificity of 97% (0.95 CI: 94.5–98.5), and could reliably identify females with less than 70% normal G6PD activity with a sensitivity of 95.5% (0.95 CI: 89.7–98.5) and specificity of 97% (0.95 CI: 94.5–98.6). The STANDARD G6PD product represents an opportunity to diagnose G6PD deficiency equally for males and females in basic clinical laboratories in high- and low-resource settings. This quantitative point-of-care diagnostic test for G6PD deficiency can provide equal access to safe radical cure of P. vivax cases in high- and low-resource settings, for males and females and may support malaria elimination, in countries where P. vivax is endemic.
Glucose-6-phosphate dehydrogenase (G6PD) is an essential enzyme that protects red blood cells from oxidative damage caused by certain drugs, diseases, and foods.1,2 The X-linked human G6PD gene is highly polymorphic with many mutations resulting in reduced enzyme activity in red blood cells or G6PD deficiency. Exposure to oxidative agents can induce hemolysis in red blood cells with low G6PD activity levels and cause severe anemia, sometimes requiring blood transfusion or causing irreversible renal damage and even mortality, if not managed promptly. Glucose-6-phosphate dehydrogenase deficiency presents clinically in the neonate as jaundice resulting from hyperbilirubinemia; this may lead to kernicterus, a form of brain damage.3,4 Several medications including rasburicase- and 8-aminoquinoline–based antimalarial drugs, such as primaquine, are known to cause clinically significant hemolysis in G6PD-deficient individuals. A high of dose primaquine (a 7-or 14-day regimen) is required to cure patients of Plasmodium vivax malaria. If a patient is not cured of P. vivax, they are at risk of relapse with increasing risk of morbidity and further transmission of the parasite.5,6 Relapse contributes to more than 50% of the disease burden in a community.7,8 A single dose of tafenoquine, another 8-aminoquinoline, when given with chloroquine is capable of curing a patient of P. vivax.9 Tafenoquine, recently approved by the United States Food and Drug Administration (FDA) for radical cure of P. vivax, under the Krintafel label, is indicated for individuals with greater than 70% G6PD activity. Tafenoquine has also been approved by the FDA with a different dosage for prophylaxis, under the Arakoda label, with similar indications for G6PD deficiency.
Performance data are presented for three G6PD activity thresholds: 1) < 30% of normal, classified as G6PD deficient, where all hemizygous G6PD-deficient males and all homozygous G6PD-deficient females lie, 2) < 70% of normal, the threshold established in the tafenoquine clinical trials for eligibility for receiving tafenoquine, and 3) < 80% of normal, the current World Health Organization threshold for defining intermediates (30–80% of normal activity) (Table 1). The Pointe Scientific assay was used as the gold standard and the 2 × 2 tables from which sensitivity and specificity values cited in Table 1 are provided as Supplemental Files 3 and 4. G6PD deficiency is the most common human genetic condition, with potential lifelong clinical implications.1,2,23 Glucose-6-phosphate dehydrogenase deficiency is highly prevalent in malaria-endemic populations, where resources are limited.24 Primaquine and tafenoquine, both 8-aminoquinolines, when given with blood-stage antimalarials can cure patients of P. vivax but may also cause clinically relevant hemolysis in patients with decreased G6PD activity. Ensuring safe, radical curative treatment requires the availability of G6PD deficiency rapid diagnostic tests that are easy-to-use and affordable.10 Qualitative tests developed in recent years attempt to address these needs but they do not accurately identify females heterozygous for G6PD deficiency with intermediate G6PD activity.12,15,25 Some of these females may be at risk of hemolysis, if exposed to the doses of 8-aminoquinolines required to eliminate hypnozoites.16,26 A point-of-care test that can measure G6PD activity normalized by hemoglobin concentration, with a broad operating temperature range could address this limitation. As per the World Health Organization prequalification technical specifications for in vitro diagnostics to measure G6PD activity, such a test must demonstrate the ability to discriminate from normal, G6PD-deficient (< 30%), and G6PD-intermediate (30–80% of normal) activity.27 The performance of the test at the inclusion threshold (> 70%) used in the clinical trials for tafenoquine is also relevant, as this will be used to inform treatment with this drug.9
Although automated and near-patient quantitative tests for G6PD deficiency have been previously described, many of which rely on fluorescence, none are widely available.18,31 The SD Biosensor STANDARD G6PD test represents a true near-patient product that provides quantitative G6PD results, bringing the possibility of managing all patients—males, females, and neonates—equally with respect to G6PD deficiency, minimizing risk of hemolysis, and improving health outcomes. Specifically, it represents a true opportunity to greatly increase access to radical cure of P. vivax malaria, and thus support malaria elimination, and provides an opportunity to address a gender gap in our understanding of G6PD epidemiology and its clinical implications.