Ask the diagnostic laboratory that you use if they have been NVSL accredited for the serology test you choose. The sensitivity is estimated to be 30 percent in cattle with pre-Stage IV infections with M. avium subs. Alternately, as with all other types of tests, a negative-test result should be regarded as not detected rather than as not present. It is not possible to tell if the positive result is from a true infection or a vaccination. It is used to identify herds at low risk of being infected.
Fecal culture is used to confirm positive-test results.
With many false positives and false negatives, the CFT is not recommended in the United States for routine diagnostic use. In general, the serologic tests are most accurate when used as screening tools to identify infected herds. They are reasonably accurate for use on individual cattle with clinical disease and are less accurate to detect individual animals with non-clinical infection with the exception of animals shedding large numbers of Johne's organisms in feces. For increased confidence in the actual disease status of an individual animal, the test result should to be interpreted in light of herd history or prevalence of Johne's disease and calculated predictive values or likelihood ratios. For greatest confidence in a positive result, it is recommended to follow a serologic test with an organism-based test such as fecal culture or DNA probe.