Test Updates

Changes to liver autoantibody screening dilution

From 21 April 2026 the screening dilution used for liver autoantibodies (mitochondrial, smooth muscle and LKM) will change from 1:40 to 1:80 for adults. The screening dilution for children under 18 will change from 1:20 to 1:40.

The current assay is designed to be run with a screening dilution of 1:100. BSG/EASL guidelines advise screening at 1:40 in adults and 1:20 in children which we implemented when we went live with the new immunofluorescence solution in January 2026. This is based on an old assay which is not routinely available now and there is no good evidence in the literature to define screening dilutions to be used with newer assays.

Using a screening dilution of 1:40 we are seeing a lot of prozone effect (false negatives due to antibody excess) and heterophilic antibody interference and false positive LKM results. To mitigate this, we have been repeating many samples at further dilutions to reduce the risk of missing strong positive results especially for smooth muscle antibodies.

It is currently difficult to distinguish between a true negative and a false negative result and we are at risk of missing positive SMAs in particular. In children we have been screening at 1:20 and 1:40 but we are having to re-run samples at 1:80 to check we are not missing anything significant.

In view of the concerns around missing the presence of strong positive antibodies we will change the screening dilutions to 1:80 for adults and 1:40 for children from 21 April 2026.