RESUMO
There has been a dramatic increase in requests for coeliac disease (CD) serological screening using immunoglobulin (Ig)A tissue transglutaminase antibodies (IgA-tTG). Recently, the UK National Institute for Health and Care Excellence has revised its guidance, recommending that total IgA should also be measured in all samples. This is justified, as false-negative results may occur with IgA deficiency. However, implementation of this guidance will incur considerable expense. Tests that measure IgA-tTG antibodies can detect IgA deficiency, indicated by low background signal. This provides an opportunity to identify samples containing IgA ≤ 0·2g/l, obviating the need for unselected IgA measurement. We investigated the feasibility of this approach in two centres that use the EliA™ Celikey™ assay or QUANTA Lite® enzyme-linked immunosorbent assay to quantify IgA-tTG antibodies. In both cases, total IgA correlated strongly with background IgA-tTG assay signal. Using the Celikey™ assay, a threshold of < 17·5 response units achieved 100% sensitivity (95% confidence intervals 79·4-100%) for detection of IgA ≤ 0·2g/l, circumventing the need for IgA testing in > 99% of sera. A similar principle was demonstrated for the QUANTA Lite® assay, whereby a threshold optical density of < 0·0265 also achieved 100% sensitivity (95% confidence intervals 78·2-100%) for IgA ≤ 0·2 g/l, avoiding unnecessary IgA testing in 67% of cases. These data suggest that CD screening tests can identify samples reliably containing low IgA in a real-life setting, obviating the need for blanket testing. However, this approach requires careful individualized validation, given the divergent efficiency with which assays identify samples containing low IgA.