Selective IgA deficiency in Japanese blood donors: frequency and statistical analysis.

The incidence of selective IgA deficiency (SIgAD) was determined in a healthy adult population of 222,597 Japanese volunteer blood donors. Of the blood donors screened, only 0.007% (1:14,840) were found to be IgA-deficient (less than 10 mg/dl) by means of the double diffusion method, while 0.005% (1:18,500) were less than 5 mg/dl, and 0.003% (1:31,800) were less than 1 mg/dl by means of the single radial immunodiffusion method. Statistical analysis of the results clearly showed that the incidence of SIgAD in Japanese blood donors is very much lower than that in blood donors of European ancestry. The Japanese population may occupy a unique position in the ethnical peculiarities. Anti-IgA antibodies were found in 3 (25.0%) of 12 IgA-deficient blood donors whose IgA levels were less than 5 mg/dl, a prevalence rate comparable to that in donors of European ancestry. Although it is difficult to develop a suitable file of IgA-deficient donors in Japan, the establishment of a Rare Donor Registry System on IgA deficiency is a matter of urgency.