https://www.vetsurgeon.org/f/clinical-questions/9961/sensitivity-of-the-tb-skin-test-decreasing Last night we had a farmers&#39; meeting on TB prevention. I was explaining what a sensitivity of 80% of the skin test means: that for every 4 reactors found, one was missed. Then a farmer asked a question which has kept me thinking since: Isn&#39;t thereen-USTelligent Community 10https://www.vetsurgeon.org/thread/50130?ContentTypeID=1Sat, 26 Nov 2011 10:10:31 GMT146601cc-3922-4be7-9974-7e1d4e45a66b:482c6188-b78f-441d-9533-d794575ab5deHannah Wynne Richards<p>All I know is that TB can remain dormant for years due to the immune response Eventually the immune response fails,which is when the animal develops clinical disease&nbsp; So you can keep testing and removing reactors,whilst the old emaciated cow who&#39;s infecting them all passes every test</p> <p>Having said that modern dairy cows rarely live long enough to get tothat stage, and that was back in the days of 3 yearly TB tests,so the active case was assumed to have been reactive in the past-just not been tested at that time</p> <p>Wynne</p><div style="clear:both;"></div>