Milk Ring Test for Brucella in cow's milk MRT PubMed: 9684294 The milk ring test is a serological test for lacteal anti-Brucella IgM and IgA bound to milk fat globules in cow or goat milk. False Positive: False positives may occur with this test in colostrum, milk at the end of a lactation period, or cows suffering from a hormonal disorder or mastitis; however the specificity is reported to be 99%. False Negative: False negatives may occur with this test in milk with a low concentration of lacteal antibodies or lacking fat-clustering factors; the sensitivity is reported to be 56%. YL, YH Immunoassay test for brucellosis