Performance of the CareStart™ G6PD Deficiency Screening Test, a Point-of-Care Diagnostic for Primaquine Therapy Screening

Abstract

Development of reliable, easy-to-use, rapid diagnostic tests (RDTs) to detect glucose-6-phosphate dehydrogenase (G6PD) deficiency at point of care is essential to deploying primaquine therapies as part of malaria elimination strategies. We assessed a kit under research and development called CareStart™ G6PD deficiency screening test (Access Bio, New Jersey, USA) by comparing its performance to quantitative G6PD enzyme activity using a standardized spectrophotometric method (‘gold standard’). Blood samples (n = 903) were collected from Cambodian adults living in Pailin province, western Cambodia. G6PD enzyme activities ranged from 0 to 20.5 U/g Hb (median 12.0 U/g Hg). Based on a normal haemoglobin concentration and wild-type G6PD gene, the normal values of G6PD enzymatic activity for this population was 3.6 to 20.5 U/g Hg (95th percentiles from 5.5 to 17.2 U/g Hg). Ninety-seven subjects (10.7%) had <3.6 U/g Hg and were classified as G6PD deficient. Prevalence of deficiency was 15.0% (64/425) among men and 6.9% (33/478) among women. Genotype was analyzed in 66 G6PD-deficient subjects and 63 of these exhibited findings consistent with Viangchang genotype. The sensitivity and specificity of the CareStart™ G6PD deficiency screening test was 0.68 and 1.0, respectively. Its detection threshold was <2.7 U/g Hg, well within the range of moderate and severe enzyme deficiencies. Thirteen subjects (1.4%, 12 males and 1 female) with G6PD enzyme activities <2 U/g Hg were falsely classified as “normal” by RDT. This experimental RDT test here evaluated outside of the laboratory for the first time shows real promise, but safe application of it will require lower rates of falsely “normal” results.

Validation of the rapid test Carestart(tm) G6PD among malaria vivax-infected subjects in the Brazilian Amazon

“…There was a high frequency of false-negatives even when using cut-offs considered low, where one would expect greater sensitivity due to lower enzyme activity in the samples tested, which is a phenomenon also observed elsewhere (22 ) and the main factor responsible for the poor performance of the Carestart™ G6PD rapid test in our study. The use of venous blood to perform the rapid test probably did not affect the sensitivity of the test.…”

“…Due to limitations of the quantitative gold standard in detecting heterozygous females, owing to lionization, females were not included in this study. The sample size was calculated for a fi nite population, using the following parameters: 1) sensitivity estimate: 0.68 (22) ; 2) specifi city estimate: 0.99 (22) ; 3) z value (alpha error of 5%): 1.96; 4) precision: 0.10 (for sensitivity) and 0.01 (for specifi city); fi nite population: 1,500 men. Base parameters assumed the following: 4.5% prevalence of G6PDd in the study population, based on the study in 3 districts of Manaus, with 1,478 men (26) ; a frequency of vivax malaria/mixed malaria of 3,000 cases/year (FMT-HVD 2012 data), and 50% of male individuals in the Brazilian population.…”

Performance of the CareStart Glucose-6-Phosphate Dehydrogenase (G6PD) Rapid Diagnostic Test in Gressier, Haiti

“…Because G6PD enzyme concentrations in patients with mild deficiency are sufficient to generate a purple color change (negative result), this test is unable to accurately determine mild forms of G6PD deficiency, which was noted in a similar study conducted in Cambodia. 13 However, these individuals are at a lower risk of DIH when treated with PQ. Likewise, using alternative antimalarial drugs to treat patients with ambiguous test results has little impact on their clinical management and represents a viable strategy to further decrease the risk of DIH.…”

Accuracy of CareStart™ G6PD rapid diagnostic test: variation in results from different commercial versions

“…Although CareStart™ G6PD rapid test has been demonstrated to have > 95% sensitivity in detecting G6PD deficient phenotypes [5][6][7][8] , there have been discrepant results. Particularly, low sensitivity among individuals with enzyme activity < 30% has been reported in Cambodia (68%) 9 and more recently in the Brazilian Amazon (61.5%) 10 .…”

“…However, no mention of a pale purple color background appeared in the first batches of CareStart TM G6PD manufacturer's instructions 11 . As a result, a pale purple background was classified as normal only by the Cambodian study, and later by the Brazilian study 9,10 . The most recent CareStart TM G6PD test instructions indicate that no color change or the appearance of a very faint purple color in the reading window within 10 min (borderline results) should be read as deficient 12 .…”