Dr. Damien Barrett:

It depends. It has better sensitivity and detects more but the specificity is not as good. That means there are more false positives. We use the blood test in circumstances where we are confident that there is cattle-to-cattle transmission going on. We generally do not use it in single reactors or where we do not believe on epidemiological grounds that cattle-to-cattle transmission is taking place because there is a risk that we would be taking out false positives.