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Background
The Rapid Fluorescent Focus Inhibition Test (RFFIT) is a specialized in vitro assay that measures virus-neutralizing antibodies against the rabies virus. It is crucial for assessing the immune response following rabies vaccination or exposure. RFFIT offers a rapid, reliable, and reproducible alternative to animal-based neutralization tests eliminating the need for live animal testing. It uses virus neutralization in combination with fluorescent microscopy to detect rabies virus replication in susceptible cells, specifically baby hamster kidney (BHK-21) cells after exposure to test serum. The test provides quantitative results enabling the measurement of neutralizing antibody titers for determining protective immunity.
The RFFIT method which aligns with international standards set by the World Health Organization and the World Organisation for Animal Health has gained widespread adoption due to its improved sensitivity and reduced testing time. Today, it remains a gold standard in rabies diagnostics used extensively in clinical, research and surveillance settings. It plays a pivotal role in determining vaccine efficacy guiding post-exposure prophylaxis and ensuring the safety of at-risk populations. The test’s robust methodology and precise quantification of neutralizing antibodies make it an essential tool in the global fight against rabies.
Indications/Applications
Post-Vaccination Immunity Assessment is a crucial tool for confirming the presence of neutralizing antibodies in individuals vaccinated against rabies. It is recommended for high-risk groups, travelers to rabies-endemic areas and those receiving post-exposure prophylaxis (PEP). Post-Exposure Prophylaxis (PEP) monitoring evaluates the effectiveness of rabies immunoglobulin and vaccine administration ensuring sufficient antibody titers are achieved. Protective Immunity Levels determine protective immunity levels and whether booster vaccinations are necessary especially in those with occupational risks or previous exposure. Rabies Exposure Investigations aid in risk assessment for initiating or modifying PEP. Preclinical and Clinical Vaccine Studies evaluate the immunogenicity of new rabies vaccines during development and measure antibody responses in test subjects.
Reference Range
The normal range is 0.1 to 15.0 IU/mL. The WHO defines an appropriate response to rabies immunization in people as a result of 0.5 IU/mL or above.
Interpretation
The Rapid Fluorescent Focus Inhibition Test (RFFIT) is a quantitative measurement of neutralizing antibodies against the rabies virus. It is used to evaluate the immune status of individuals or animals, guide clinical decisions and assess vaccine efficacy. The interpretation of RFFIT results depends on the antibody titer and the clinical context.
Protective Immunity (Titer ≥ 0.5 IU/mL) indicates adequate levels of neutralizing antibodies capable of providing protection against rabies virus infection. No further immediate action is needed and this is common in individuals who have completed pre-exposure prophylaxis (PrEP) or post-exposure prophylaxis (PEP). Insufficient Immunity (Titer < 0.5 IU/mL) suggests insufficient levels of neutralizing antibodies to ensure protection and may require booster vaccination especially in high-risk individuals like occupational groups (veterinarians, laboratory workers) or individuals exposed to a confirmed or suspected rabid animal.
Undetectable or Minimal Neutralizing Antibodies (Titer < 0.1 IU/mL) indicates no or negligible detectable immunity against the rabies virus. Immediate action is required like starting post-exposure prophylaxis (PEP) in case of potential exposure. This result may occur in unvaccinated individuals or immunocompromised individuals who failed to respond adequately to vaccination.
Collection And Panels
Sample type: Serum
Sample collection tube: Red top, gel barrier or serum separator tube (SST)
Sample volume: 2 mL
Sample minimum volume: 0.5 mL
Sample stability: Samples are stable for 2 weeks at room temperature, 9 months in refrigerator and 1 year in frozen condition.
Unacceptable sample: Grossly hemolyzed or lipemic samples are not acceptable.
References
Both our subscription plans include Free CME/CPD AMA PRA Category 1 credits.
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