Frequency of selective IgA deficiency among Brazilian blood donors and healthy pregnant women.

Selective IgA deficiency (SIgAD) is the most common primary immunodeficiency, with frequencies ranging from 1:300 to 1:3,000 in populations surveyed in Europe and the US. In the present study we tested 11,576 clinically healthy persons (blood donors and pregnant women) for SIgAD (serum IgA less than 5 mg%). Serum samples were screened by double immunodiffusion with a sheep anti-human alpha-chain (minimal detection level of 30 mg%). Samples showing negative or doubtful reactions were submitted to the radial immunodiffusion test (minimal detection level of 0.5 mg%). For the samples with low or undetectable IgA levels, IgG and IgM concentrations were also determined. We found 12 individuals with SIgAD and 2 with deficiency of the 3 immunoglobulin classes. The prevalence of SIgAD in this Brazilian population (1:965) is equivalent to values reported for other countries.