What is the role of spectrophotometric assays in the workup of glucose-6-phosphate dehydrogenase (G6PD) deficiency?

Updated: Jun 25, 2020
  • Author: Lawrence C Wolfe, MD; Chief Editor: George T Griffing, MD  more...
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Answer

Quantitative test:

  • Spectrophotometric assay: Quantitative tests for G6PD activity are considered the criterion standard. The rate of NADPH generation is spectrophotometrically measured at a wavelength of 340 nm. The G6PD activity is finally expressed as G6PD IU/red blood cell and G6PD IU/hemoglobin ratios. In normal red blood cells, the G6PD activity ranges from 7-10 IU/g Hb, when measured at 30 C. [6, 7, 8]  Testing for enzyme activity should not be performed during episodes of acute hemolysis, as results may be falsely negative. Senescent red blood cells are more vulnerable to hemolysis due to their diminished G6PD levels. Compensatory increase of immature young red cells with increased G6PD levels usually occurs in state of acute hemolysis, and hence results could be altered.

A study by Peters et al indicated that in the detection of heterozygously G6PD-deficient females, spectrophotometry, cytofluorometry, and chromate inhibition have a sensitivity of 0.52, 0.85, and 0.96, respectively, and a specificity of 1.00, 0.88, and 0.98, respectively. The investigators stated that although routine means of assessing total G6PD activity can miss heterozygously G6PD-deficient females in whom a larger percentage of red blood cells is G6PD-sufficient, chromate inhibition and cytofluorometry can detect most of these cases. [9]


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