Since then, rapid tests on over 28,000 samples have been conducted. These rapid tests are run once, and, if reactive, run again in duplicate.

“According to manufacturer's instructions, if either of the duplicate tests is reactive, the test is deemed inconclusive and confirmatory testing is performed using the immunohistochemistry (IHC) test--the gold standard test for BSE.

During the initial few months of our testing program as participating laboratories gained proficiency in using the tests, APHIS declared a test inconclusive on the basis of the results of only the first test. To date, two samples have been declared inconclusive for BSE, but have proven to be negative for the disease according to IHC testing.

“APHIS has now completed proficiency testing of all the BSE labs, including reviewing data from the first 60 days of testing. Based on this review, APHIS will now wait until the duplicate or second-run tests are conducted before declaring a test sample inconclusive.

If either of the tests in the second run is reactive, APHIS will announce this result as an inconclusive and will conduct confirmatory testing at National Veterinary Services Laboratories in Ames, Iowa (NVSL).“

Source: Animal and Plant Health Inspection Service - 4th August 2004