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Although IgA deficiency (IgAD) is currently recognised as the most frequent immunodeficiency in humans,1 individuals with IgAD are largely considered to be healthy and when discovered are usually not investigated further or followed up.2 The rare occasion when IgAD is a cause for concern is when these individuals require blood or blood products, in which case current practice advises that products not containing IgA must be administered. On these occasions it is also often, but not always, practice to check for the presence of anti-IgA antibodies, the importance of which is still frequently disputed (vide infra3).
Are we doing what we should? Are the above practices justified by currently existing data?
What are the clinical consequences of IgAD?
Total IgAD is defined in most studies as selectively undetectable IgA at a value of 0.05 g/litre. However, there is no consensus regarding this value and some UK referral centres are now moving the cut off point to 0.0016 g/litre by using more sensitive techniques.4 The limit of sensitivity differs greatly depending on the method used, namely: 0.2 g/litre for nephelometry, 0.05 g/litre for low level radial immunodiffusion plates, and 0.0016 g/litre for haemaglutination inhibition techniques. Partial IgAD refers to detectable but reduced IgA, more than 2 SD below the low end of age matched, normal range values, and this is mostly seen in children under 5 years of age; about half of these children reach normal values by 14 years (transient IgAD).2 The data discussed below refer to total IgAD unless stated otherwise.
Although we consider IgAD to be the most frequent immune deficiency (found in one in 700 healthy blood donors), it must be stressed that this applies only to the Western world because the prevalence differs with ethnic background, and is only one in 18 500 among Japanese blood donors. …