Comparison between the chromate inhibition test and a cytochemical method for the determination of glucose-6-phosphate dehydrogenase deficiency in erythrocytes.

The sensitivity and specificity of the chromate inhibition test for the determination of glucose-6-phosphate dehydrogenase (G6PD) deficiency in erythrocytes were compared with a cytochemical staining method. Fifty blood samples were used in a double blind study. The samples were selected from 600 blood samples on the basis of two biochemical criteria, viz. either G6PD activity less than 4.8 IU/g Hb as analysed spectrophotometrically and/or G6PD activity less than glutathione reductase (GSSG-R) activity. The cytochemical assay was taken as reference because it has been proved to be sensitive and specific for the detection of heterozygous and homo/hemizygous forms of deficiency. Cytochemically, one hemizygously deficient patient, 19 heterozygotes and 30 normals were detected. When applying the chromate inhibition test a somewhat different result was obtained with the same samples: one of the 30 normals was classified as heterozygously deficient (3% false positives) and 5 of the 19 heterozygously deficient patients were classified as normal (26% false negatives). It is concluded that the chromate inhibition test is a more sensitive biochemical test than the fluorescence spot test or spectrophotometric assays. However, it is less reliable than the cytochemical test for the detection of heterozygously G6PD deficient patients.