The value of methemoglobin reduction test as a screening test for neonatal glucose 6-phosphate dehydrogenase deficiency.

Glucose 6-phosphate dehydrogenase (G-6-PD) deficiency is common in the Thai population and is the cause of neonatal hyperbilirubinemia and hemolytic anemia. This X-linked disorder is much more common in males than females. The objectives of this study were to compare the result of the screening methemoglobin reduction test (MRT) with the gold standard G-6-PD activity, and also to determine the prevalence of G-6-PD deficiency in the cord blood and blood of neonates with hyperbilirubinemia. Five hunderd and twenty two randomly selected cord blood (350 males, 172 females) and 229 peripheral blood from neonates with hyperbilirubinemia were assayed for G-6-PD enzyme activity using a WHO-recommended standard test as well as methemoglobin reduction (MR) test. The results showed that prevalence of G-6-PD deficiency from the cord blood was 11.1 per cent in males, and 5.59 per cent in females. Among newborns with neonatal jaundice, the prevalence of G-6-PD deficiency was 22.1 per cent in males and 10.1 per cent in females. MRT in cord blood G-6-PD deficiency screening had acceptable sensitivity (85.7%) and high specificity (98.1%). The sensitivity of MRT in jaundiced infants was low (60.0%) whereas the specificity was acceptable (92.1%). The negative predictive values were more than 90 per cent while the positive predictive values were low (61-65%) from both specimens. Conclusions: G-6-PD deficiency is common in the Thai population, both in males and females and can be screened from cord blood by using low cost MRT. G-6-PD deficiency contributes to 20 per cent of neonatal jaundice, and screening with MRT yields low sensitivity.

The thalassemic red cell membrane.

The underlying cause of pathology in thalassemia is the premature destruction of red cells, both in the bone marrow and by the reticuloendothelial system. It is generally accepted that the presence of unpaired excess globin chains is the primary circumstance leading to such membrane alterations as oxidation of phospholipids, modification of cytoskeletal proteins and their interactions, reduced membrane-associated ATPase activities, and enhanced permeability of cations. Such perturbations in turn result in the exposure of outer surface neoantigens, enhanced binding of autoantibodies and complement fixation to the outer red cell surface. These factors contribute to the observed distinctive morphologies, increased rigidity and decreased deformability of the thalassemic red cells. In alpha-thalassemic red cells, excess beta-globin chains form homotetramers, Hb H, which are relatively stable and will only damage red cell membrane when precipitated as inclusion bodies, whereas excess alpha-globin chains cannot form such homotetramers and upon synthesis rapidly bind to the cytoplasmic side of the beta-thalassemic red cell membrane, even in young erythroblasts. This difference in properties of the excess globin chains may offer an explanation for the variation in clinical severity observed between these two forms of thalassemia.