More on Rabies Titers (RFFIT vs ELISA)

Was your rabies titer determined by the ELISA test?  If so, you need to find another lab!  According to a rabies authority, the RFFIT type test is the only internationally approved procedure for measuring rabies neutralizing antibody.  The key word here is neutralizing. The ELISA test measures ANY antibody that can attach to rabies antigen and many antibodies that attach to a pathogen are not necessarily neutralizing antibody. So a positive ELISA test may not be a positive RFFIT test. This can be dangerous given the fatal nature of rabies. The RFFIT (rapid fluorescent foci inhibition test),  the FAVN (fluorescent antibody virus neutralizing), and the TC/SN (tissue culture serum neutralizing) are all tests that measure only that antibody that will kill live rabies virus.  Patient serum is diluted out, and each dilution is mixed with live rabies virus. The mixtures are then put onto cell culture to detect what virus was not killed by the serum.  All three mentioned neutralizing tests are comparable and acceptable in measuring serum neutralizing antibody. The CDC uses the RFFIT test.  Other labs use a TC/SN test that gives the exact same results. ELISA tests to measure rabies antibody are unfortunate. The reason the neutralizing tests are so far and few between is because they can only be done in labs approved to work with live rabies virus and those labs that have the practiced expertise to do these tests. I would definitely recommend Kansas State as the only commercial lab in the US that does a neutralizing test.