The value of screening tests for glucose-6-phosphate dehydrogenase deficiency

The performances of two commercial screening tests for glucose-6-phosphate dehydrogenase deficiency (Sigma fluorescent spot test and Sigma colorimetric method) were assessed in order to determine their usefulness in a routine haematology laboratory. As a first step, three ranges for enzyme activity were determined as follows: a 'normal' range determined from the 95% confidence limit of assays carried out on 114 normal adult males, a deficient range calculated as 25% of the upper limit of normal or less, and an intermediate range between the lower and upper values of these ranges. These values were 4.9-11.8 u/g Hb, 0-2.9 u/g Hb and 3.0-4.8 u/g Hb respectively. A separate normal range was also determined for females and was 5.5-12.8 u/g Hb. The two screening tests were then assessed against these values and the kits were found to be equally reliable at predicting normals and deficients but less reliable at detecting all female heterozygotes. The criteria for using the different procedures were evaluated. It is concluded that screening procedures are useful only when a large number of tests are routinely performed or in the absence of facilities for assays, as they offer no advantage in cost or time over the assay procedure. The colorimetric test (single vials) is easier and cheaper to use if isolated tests are performed, whereas the fluorescent spot test (with some modifications) is more useful for carrying out numerous tests simultaneously.