Field evaluation of a novel semi-quantitative point-of-care diagnostic for G6PD deficiency in Indonesia

BACKGROUND

The WHO recommends routine testing of G6PD activity to guide radical cure in patients with Plasmodium vivax malaria. Females may have intermediate G6PD enzyme activity and to date, only complex diagnostics are able to reliably identify them. The semi-quantitative G6PD diagnostic "One Step G6PD Test" (Humasis, RoK; "RDT") is a lateral flow assay that can distinguish deficient, intermediate, and normal G6PD status and offers a simpler diagnostic alternative.

METHODS

G6PD status of participants enrolled in Malinau and Nunukan Regencies and the capital Jakarta was assessed with the RDT, and G6PD activity was measured in duplicate by reference spectrophotometry. The adjusted male median (AMM) of the spectrophotometry measurements was defined as 100% activity; 70% and 30% of the AMM were defined as thresholds for intermediate and deficient G6PD status, respectively. Results were compared to those derived from spectrophotometry at the clinically relevant G6PD activity thresholds of 30% and 70%.

RESULTS

Of the 161 participants enrolled, 10 (6.2%) were G6PD deficient and 12 (7.5%) had intermediate G6PD activity by spectrophotometry. At the 30% threshold, the sensitivity of the RDT was 10.0% (95%CI: 0.3-44.5%) with a specificity of 99.3% (95%CI: 96.4-100.0%); the positive predictive value was 50.0% (95%CI: 1.3-98.7%) and the negative predictive value 94.3% (95%CI: 89.5-97.4%). The corresponding figures at the 70% threshold were 22.7% (95%CI: 7.8-45.4%), 100.0% (95%CI: 97.4-100.0%), 100.0% (95%CI: 47.8-100.0%) and 89.1% (95%CI: 83.1-93.5%), respectively.

CONCLUSION

While there is a dire need for an easy-to-use, economical, semi-quantitative diagnostic for the point of care, the observed performance of the "One Step G6PD Test" in its current form was insufficient to guide antimalarial treatment.

Field assessment of the operating procedures of a semi-quantitative G6PD Biosensor to improve repeatability of routine testing

In remote communities, diagnosis of G6PD deficiency is challenging. We assessed the impact of modified test procedures and delayed testing for the point-of-care diagnostic STANDARD G6PD (SDBiosensor, RoK), and evaluated recommended cut-offs. We tested capillary blood from fingerpricks (Standard Method) and a microtainer (BD, USA; Method 1), venous blood from a vacutainer (BD, USA; Method 2), varied sample application methods (Methods 3), and used micropipettes rather than the test's single-use pipette (Method 4). Repeatability was assessed by comparing median differences between paired measurements. All methods were tested 20 times under laboratory conditions on three volunteers. The Standard Method and the method with best repeatability were tested in Indonesia and Nepal. In Indonesia 60 participants were tested in duplicate by both methods, in Nepal 120 participants were tested in duplicate by either method. The adjusted male median (AMM) of the Biosensor Standard Method readings was defined as 100% activity. In Indonesia, the difference between paired readings of the Standard and modified methods was compared to assess the impact of delayed testing. In the pilot study repeatability didn't differ significantly (p = 0.381); Method 3 showed lowest variability. One Nepalese participant had <30% activity, one Indonesian and 10 Nepalese participants had intermediate activity (≥30% to <70% activity). Repeatability didn't differ significantly in Indonesia (Standard: 0.2U/gHb [IQR: 0.1-0.4]; Method 3: 0.3U/gHb [IQR: 0.1-0.5]; p = 0.425) or Nepal (Standard: 0.4U/gHb [IQR: 0.2-0.6]; Method 3: 0.3U/gHb [IQR: 0.1-0.6]; p = 0.330). Median G6PD measurements by Method 3 were 0.4U/gHb (IQR: -0.2 to 0.7, p = 0.005) higher after a 5-hour delay compared to the Standard Method. The definition of 100% activity by the Standard Method matched the manufacturer-recommended cut-off for 70% activity. We couldn't improve repeatability. Delays of up to 5 hours didn't result in a clinically relevant difference in measured G6PD activity. The manufacturer's recommended cut-off for intermediate deficiency is conservative.

Determining a critical threshold for G6PD activity below which red blood cell response to oxidative stress is poor

Background

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common enzyme disorder in the world. Its main function is to generate NADPH that is required for anti-oxidative pathway in the cells especially in red blood cells (RBC). G6PD deficiency is X-linked and thus subject to random X-chromosome inactivation in women giving them mosaic expression of G6PD activities in their individual cells. This phenomenon makes it difficult for diagnosis with the currently available G6PD qualitative diagnostic tests. With the rolling out of newly marketed anti-malarial drug tafenoquine, which has a long half-life, screening for G6PD deficiency becomes a necessity where those with < 70% G6PD activity cannot receive this drug. Thus, evidence for a quantitative cut-off for G6PD activity is needed to ensure safe drug administration.

Methods

RBC models were developed to analyse the effect of oxidant on RBC oxidative markers namely total glutathione (GSH)and malondialdehyde (MDA). G6PD activity was measured using quantitative assay from Trinity Biotech and was correlated with cytofluorometric assay. RBC from two G6PD heterozygous women with different G6PD activities were also analysed for comparison.

Results

There was a negative correlation between G6PD activity and CuCl concentration and a strong association between G6PD activities and proportion of G6PD normal RBC in CuCl-treated models and in ex vivo RBC. However, in terms of oxidative stress markers analyses, unlike the hypothesis where the lower G6PD activity, the higher MDA and the lower GSH level, the CuCl RBC model showed that in low G6PD activities (10–30%) cells, the MDA level is lower compared to the rest of the models (p < 0.05). The ex vivo models however were in line with the hypothesis, although the result was not significant (p = 0.5). There was a significant difference between RBC with < 60% and those with > 80% G6PD activities in CuCl RBC model, but not in ex vivo RBC (p = 0.5). Genotyping heterozygous subjects showed G6PDViangchan variant with 2.97 U/gHb (33% activity) and 6.58 U/gHb (74% activity).

Conclusions

The GSH analysis has pointed to the 60% G6PD activity cut-off and this data is supportive of the old World Health Organization threshold for intermediate upper limit of 60% G6PD activity. However, there are significant limitations in using MDA assay with CuCl RBC model because the RBC was already stressed due to the copper treatment and thus present a different result when compared to the ex vivo model.

Accurate light microscopic diagnosis of South-East Asian ovalocytosis

INTRODUCTION

South-East Asian ovalocytosis (SAO) is a common inherited red blood cell polymorphism in South-East Asian and Melanesian populations, coinciding with areas of malaria endemicity. Validation of light microscopy as a diagnostic alternative to molecular genotyping may allow for its cost-effective use either prospectively or retrospectively by analysis of archived blood smears.

METHODS

We assessed light microscopic diagnosis of SAO compared to standard PCR genotyping. Three trained microscopists each assessed the same 971 Giemsa-stained thin blood films for which SAO genotypic confirmation was available by PCR. Generalized mixed modeling was used to estimate the sensitivity, specificity, positive predictive value, and negative predictive value of light microscopy vs "gold standard" PCR.

RESULTS

Among red cell morphologic parameters evaluated, knizocytes, rather than ovalocytic morphology, proved the strongest predictor of SAO status (odds ratio [OR] = 19.2; 95% confidence interval [95% CI] = 14.6-25.3; P ≤ 0.0001). The diagnostic performance of a knizocyte-centric microscopic approach was microscopist dependent: two microscopists applied this approach with a sensitivity of 0.89 and a specificity of 0.93. Inter-rater reliability among the microscopists (κ = 0.20) as well as between gold standard and microscopist (κ = 0.36) underperformed due to misclassification of stomatocytes as knizocytes by one microscopist, but improved substantially when excluding the error-prone reader (κ = 0.65 and 0.74, respectively).

CONCLUSION

Light microscopic diagnosis of SAO by knizocyte visual cue performed comparable to time-consuming and costlier molecular methods, but requires specific training that includes successful differentiation of knizocytes from stomatocytes.