How is glucose-6-phosphate dehydrogenase (G6PD) deficiency diagnosed?

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

Semi-quantitative tests

The fluorescent spot test is a direct test that measures the generation of reduced nicotinamide adenine dinucleotide phosphate (NADPH) from nicotinamide adenine dinucleotide phosphate (NADP+); the test is positive if the blood spot fails to show fluorescence under ultraviolet light. It is rapid, simple, sensitive, and inexpensive. [6, 7, 8]

The methemoglobin reduction test is a rapid indirect test that measures the reduced methemoglobin levels produced after NADPH oxidation. [6]

The cytofluorimetric test is a cytochemical typing assay that provides a fluorometric readout of the classic methemoglobin reduction test at the level of an individual red blood cell. [7]

Quantitative tests

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. [6, 7, 8]

Spectrophotometric quantitation may fail to detect deficiency in heterozygous females, due to residual activity in G6PD-sufficient cells. Regarding the identification of G6PD-deficient, as well as G6PD-sufficient, cells by a cytochemical method or cytofluorometry, these analyses are more sensitive in testing for G6PD deficiency in females. [9]


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