Performance Advantages of the Glucose-6-Phosphate Dehydrogenase Assay Kit (Substrate Method) from a Methodological Comparison Perspective

Overview of G6PD Activity Detection Methods

Laboratory methods for determining glucose-6-phosphate dehydrogenase (G6PD) activity mainly include the fluorescent spot test (qualitative/semi-quantitative), the ultraviolet rate method (quantitative), and the substrate method developed in recent years. The fluorescent spot test is simple to perform and suitable for large-scale screening at the primary level, but result interpretation relies on subjective experience and cannot achieve precise quantification. The ultraviolet rate method calculates enzyme activity by continuously monitoring the rate of NADPH generation and is a classic method currently adopted by various automated biochemical analyzers; however, it has high requirements for reagent formulation and reaction conditions and may be affected by endogenous interfering substances. The glucose-6-phosphate dehydrogenase assay kit (glucose-6-phosphate substrate method) is improved on the basis of the traditional rate method by optimizing substrate concentration and buffer system, aiming to improve the linear range and anti-interference capability of the assay.

Reaction System Design and Specificity of the Substrate Method

The core of the substrate method is the selection of glucose-6-phosphate sodium salt as the substrate, with the reaction carried out in the presence of excess coenzyme NADP⁺. The kit usually uses Tris or phosphate buffer, with pH generally controlled between 7.8 and 8.2. In common specifications, the substrate concentration is designed to facilitate discrimination of the enzyme activity range between normal and deficient samples. Compared with the ultraviolet rate method, the substrate method adds selective inhibitors or stabilizers to the formulation to minimize the synergistic interference of 6-phosphogluconate dehydrogenase (6PGD). Because 6PGD also catalyzes the subsequent reaction to generate NADPH, if the reagent does not inhibit it, the activity measurement result will be falsely elevated, leading to misclassification of intermediate deficiency. Some substrate method kits improve the specificity for G6PD determination by balancing the ratio of glucose-6-phosphate to 6-phosphogluconate or by adding specific inhibitors (such as cis-aconitic acid).

Precision, Linear Range, and Automation Compatibility

In performance verification, the glucose-6-phosphate dehydrogenase assay kit (glucose-6-phosphate substrate method) generally requires a coefficient of variation of less than 5% near the upper and lower limits of the normal reference interval, and in the low-activity region (such as 5–30 mU/10⁹ red blood cells) it must meet clinically allowable error. Its linear range can usually cover from the upper limit of normal values to the low-activity region, and common specifications can report a lower limit as low as 1–2 mU/10⁹ red blood cells. On automated biochemical analyzers, the stability of substrate method reagents after opening is generally up to 7–14 days (depending on storage conditions), and most reagents are liquid ready-to-use, requiring no reconstitution, which reduces operational errors. Because the reaction is carried out at 340 nm, the service life of the light source lamp and temperature control accuracy should be considered when selecting an instrument. Laboratories can request matching parameters from reagent manufacturers according to daily sample volume and instrument brand.

Methodological Limitations and Laboratory Selection Strategies

Although the substrate method has improved interference suppression, some inherent limitations still require attention. First, the accuracy of red blood cell counting in samples directly affects the calculation method of activity results (commonly IU/g Hb or U/10⁹ red blood cells), so precise hematocrit or hemoglobin concentration data are needed for coordination. Second, enzyme activity in severely hemolyzed or old samples may decrease irreversibly, and testing should be performed as soon as possible after sampling. In addition, for variant G6PD (such as the Mediterranean variant), its enzyme kinetic characteristics differ from those of the wild type, and the substrate method may have certain deviations; when necessary, it is recommended to combine with genotyping. When selecting kits, laboratories should comprehensively evaluate the G6PD deficiency mutation spectrum of the local population, instrument compatibility, cost-effectiveness, and availability of quality control materials. Overall, while ensuring quantitative accuracy, the substrate method improves anti-interference capability and is suitable as an alternative option for routine testing or newborn screening in medium- and large-sized laboratories.