Due to the results from factories in Silvercrest and Liffey Meats in Ireland and Dalepak in the U.K., the FSA asks food laboratory IdentiGEN for a retest of beef samples. According to the Irish Times, IdentiGEN uses a DNA profile and can pinpoint the amount of horse DNA in the samples:

The DNA technology used to test the meat, sometimes referred to as DNA fingerprinting or profiling, was developed by Alec Jeffreys at the University of Leicester back in 1984. It allowed one DNA profile to be compared directly with another.

The tests confirm that the FSA's findings are correct. They also test for phenylbutazone, a chemical used on horses that are not for consumption and is toxic to humans. Tests do not show any traces of it in the meat, meaning that the horsemeat that is contaminating the beef in the Irish supermarkets is not dangerous.