Rabies Vaccine Response End Point Titer

The Rabies Vaccine Response End Point Titer test contains 1 test with 1 biomarker.

Rabies Vaccine Response End Point Titer

Clinical Significance

Rabies Vaccine Response End Point Titer - What is "The RFFIT"?
RFFIT stands for Rapid Fluorescent Foci Inhibition Test. It is a serum neutralization (inhibition) test, which means it measures the ability of rabies specific antibodies to neutralize rabies virus and prevent the virus from infecting cells. These antibodies are called rabies virus neutralizing antibodies (RVt4A). The RFFIT does not measure the amount of rabies specific antibodies but the neutralizing activity of the antibodies present in the serum. In the test, your serum (the non-cellular portion of your blood) is first diluted fivefold (1 part serum in 4 parts diluent). Further (serial fivefold) dilutions are performed, each of which contain less and less of your serum. These serum dilutions are mixed with a standard amount of live rabies virus and incubated. Whatever RVNA is present will neutralize the virus. Next, some tissue culture cells are added and the serum/virus/cells are incubated together. Whatever rabies virus is left (i.e., that which has not been neutralized by the antibody in your serum), will infect the cells and this can be seen under the microscope through the use of specific staining. Calculation of the endpoint titer is made from the percent of virus infected cells observed on the slide.

What does your result tell you?
The RFFIT test can be used in two ways: To determine an RVNA titer (e.g.,1:5) or to determine a value for R/NA concentration (e.g.,0.1 IU/mL). The IU stands for International Unit and is calculated from the titer by comparing it against a standard reference serum. We use the following formula: Sample titer divided by the reference serum titer, multiplied by the IU/mL value of the reference serum.
Example: Your titer is 1:100, the reference serum titer is 1:200, and the value of the reference serum is 2.0 IU/mL. Using the formula: (100/200) X 2.0 IU/ml =10 IU/mL the potency of RVNA in your serum is therefore 1.0 IU/mL. Because the RFFIT test is a biological system using live cells, infectious virus, and antibodies, the reference serum can vary in titer level for each batch of testing (within an established acceptable range). Therefore the calculation of IU/mL depends on the titer of the reference serum measured in the batch tested - In general, you can take the titer value divided by 100 to get a rough estimate of the IU/mL value. To obtain the exact value you must use the calculation with the measured reference serum titer value. Current ACIP recommendations state evidence of complete neutralization at a serum dilution of 1:5 in RFFIT testing is considered an adequate response to rabies vaccination (1). The ACIP recommends reporting RFFIT results in IU/mL format (1). The RFFIT method has been validated in our laboratory and the level at which there is complete neutralization at serum dilution of 1:5 is equivalent to 0.1 UI/mL. If your serum diluted to 1:5 cannot neutralize virus (reported result is <0.1 IU/mL), booster dose may be recommended (for people determined to be at risk of rabies virus exposure - See ACIP recommendations).

Reference Range(s)