Reference and point-of-care testing for G6PD deficiency: Blood disorder interference, contrived specimens, and fingerstick equivalence and precision

Abstract

Certain clinical indications and treatments such as the use of rasburicase in cancer therapy and 8-aminoquinolines for Plasmodium vivax malaria treatment would benefit from a point-of-care test for glucose-6-phosphate dehydrogenase (G6PD) deficiency. Three studies were conducted to evaluate the performance of one such test: the STANDARD™ G6PD Test (SD BIOSENSOR, South Korea). First, biological interference on the test performance was evaluated in specimens with common blood disorders, including high white blood cell (WBC) counts. Second, the test precision on fingerstick specimens was evaluated against five individuals of each, deficient, intermediate, and normal G6PD activity status. Third, clinical performance of the test was evaluated at three point-of-care settings in the United States. The test performed equivalently to the reference assay in specimens with common blood disorders. High WBC count blood samples resulted in overestimation of G6PD activity in both the reference assay and the STANDARD G6PD Test. The STANDARD G6PD Test showed good precision on multiple fingerstick specimens from the same individual. The same G6PD threshold values (U/g Hb) were applied for a semiquantitative interpretation for fingerstick- and venous-derived results. The sensitivity/specificity values (95% confidence intervals) for the test for G6PD deficiency were 100 (92.3-100.0)/97 (95.2-98.2) and 100 (95.7-100.0)/97.4 (95.7-98.5) for venous and capillary specimens, respectively. The same values for females with intermediate (> 30% to ≤ 70%) G6PD activity were 94.1 (71.3-99.9)/88.2 (83.9-91.7) and 82.4 (56.6-96.2)/87.6(83.3-91.2) for venous and capillary specimens, respectively. The STANDARD G6PD Test enables point-of-care testing for G6PD deficiency.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1. Correlation between the STANDARD G6PD Test result and that of the reference assay as performed in the clinical laboratory.

Specimens with a white blood cell (WBC) count of > 30 x 109 cells/L are represented by the solid black circles. All other study samples are indicated by the open circles. The clinical laboratory performs WBC depletion on all specimens with WBC counts > 30 x 109 cells/L. (A) Linear regression plot for the STANDARD G6PD Test run on whole blood and the reference assay run on whole blood or depleted blood according to laboratory protocols. (B) Linear regression plot for the STANDARD G6PD Test and the reference assay, both run on whole or depleted blood according to laboratory protocols.

Fig 2. Linear correlations for STANDARD G6PD Test and reference G6PD values on contrived specimens spanning the medical decision limits.

(A) Correlation between the Pointe Scientific reagent kit run on a spectrophotometer at one laboratory (PATH, Washington, USA) and on an automated clinical chemistry analyzer at a second laboratory (University of Washington Medical Center—Northwest clinical laboratory [UWMC-NW], Washington, USA). (B) Correlation between the STANDARD G6PD Test and normalized (to percent G6PD activity) UWMC-NW laboratory reference G6PD values. Solid lines represent the linear regression fits.

Fig 3. Fingerstick precision for the STANDARD G6PD Test.

Fifteen study participants with G6PD deficient, intermediate, and normal activity on the STANDARD G6PD Test were tested on both hands by two operators across four fingers (two per hand), for a total of eight STANDARD G6PD Test runs. (A) STANDARD G6PD Test results per study participant. (B) Hemoglobin test results per study participant.

Fig 4. Histogram representation of the G6PD activity distributions in (A) females and (B) males.

The reference G6PD values (U/g Hb) were normalized using the male medians and are presented here in percent activity.

Fig 5. Receiver operating characteristics for the STANDARD G6PD Test against the reference assays for G6PD in capillary specimens.

Discrimination of G6PD deficient males and females (≤ 30% G6PD activity) from females with intermediate activity and males and females with normal activity (dark blue); discrimination of females with intermediate activity (> 30% and ≤ 70% G6PD activity) from females with normal G6PD activity (red); and discrimination of females with intermediate activity (> 30% and ≤ 80% G6PD activity) from females with normal G6PD activity. (green), for (A) capillary specimens and (B) venous specimens.