Comparison of the sensitivity of the caudal fold skin test and a commercial gamma-interferon assay for diagnosis of bovine tuberculosis.

A study to determine and compare the sensitivity of the caudal fold tuberculin test (CFT) and a commercial gamma-interferon (gamma-IFN) assay for diagnosis of bovine tuberculosis was conducted. A dairy herd with approximately a third of the cattle infected with Mycobacterium bovis was chosen for this study. All cattle from this herd were slaughtered, and tissue specimens for bacteriologic culturing and histologic examination were collected. Results of the CFT and gamma-IFN assay were compared with results of bacteriologic culturing and histologic examination to determine test sensitivity. Results were analyzed, using each of the following 4 standards to classify cattle as infected: positive test result by bacteriologic culturing only; histologic examination only; bacteriologic culturing and histologic examination; and bacteriologic culturing or histologic examination. Sensitivity of the CFT ranged from 80.4 to 84.4%, depending on the standard of comparison. Sensitivity of the gamma-IFN assay ranged from 55.4 to 97.1%, depending on the standard of comparison and on the method of interpretation. The CFT was significantly (P < 0.001) more sensitive than the gamma-IFN assay for diagnosis of bovine tuberculosis when the gamma-IFN assay was conducted and interpreted as instructed by the manufacturer. Maximum overall sensitivity was achieved when results of the CFT and gamma-IFN assay were interpreted in parallel.