Incidence study of heterozygous beta-thalassemia in northern Taiwan.

Determined with automated cell counters, mean corpuscular volume (MCV) of erythrocytes was screened in 4,100 consecutive gravidas who delivered at the National Taiwan University Hospital during the period from July 1986 through August 1988. In total, 248 (6%) women had MCV less than 80 fl and were recruited for further study, including Hb A2 quantitation using microcolumn chromatography, cord blood Hb electrophoresis on cellulose acetate membrane, and alpha-globin gene mapping in some cases. In the first control group of 51 cases of obligate carriers of heterozygous beta-thalassemia, the mean MCV +/- standard deviation (SD) was 67 +/- 4.5fl (range 59 to 76fl) and the mean Hb A2 +/- SD was 6.53 +/- 1.31% (range 4.3 to 8.0%). In the second control group of 40 cases of obligate carriers of heterozygous alpha-thalassemia 1, the mean MCV +/- SD was 70 +/- 3.7fl (range 63 to 78fl) and the mean Hb A2 +/- SD was 2.28 +/- 0.54% (range 1.5 to 3.8). Forty-five microcytic women (1.1%) had Hb A2 over 4%, a cut-off level for heterozygous beta-thalassemia in our laboratory. In this study group, the mean MCV +/- SD was 68 +/- 5.4 and the mean Hb A2 +/- SD was 6.03 +/- 1.41. None of the newborns delivered by these women had Hb Bart's in cord blood. alpha-Globin gene mapping using DNA hybridization was done in 14 women, and the results were all compatible with the exclusion of deletional alpha-thalassemia. It is concluded that approximately 1% of people in northern Taiwan are beta-thalassemia heterozygotes.