Antirabies antibody testing - Seroneutralisation test (RFFIT)

Test Description

Specifications:

Serum neutralization using the RFFIT method for determining the titer of antibodies against the rabies virus. This test can be performed either to monitor vaccine-induced immunity or as part of an ante-mortem diagnosis in a clinically suspected patient.

After preventive or curative rabies vaccination, this test can be used to assess the vaccination status of a patient. In the context of diagnostics, serology has limited sensitivity since seroconversion does not occur in every infected patient. For this test, paired serum samples must be submitted, taken at an interval of 7 to 10 days. Both blood samples must be collected before rabies immunoglobulins and/or vaccine are administered.

Results:

Quantitative test.
Titer of neutralizing antibodies expressed in International Units (IU)/ml.

• In case of diagnosis: An increase in titer between the first and second blood sample is indicative of a rabies virus infection.
• In case of vaccine monitoring: A titer of 0.5 IU/ml or higher indicates an immune response to the vaccine.

1. For checking immunity after preventive vaccination:

• < 0.5 IU/ml: no protection
• ≥ 0.5 IU/ml: priming is successful – long-term boostable

A minimum titer of 3 IU/ml is recommended for:

• Persons at high risk of exposure such as lab staff working with rabies and Lyssavirus and professionals or hobbyists frequently in contact with bats
• Persons who might not be able to receive booster treatment within 48 hours of exposure (e.g., in remote areas)

2. For checking immunity after curative vaccination:

• < 0.5 IU/ml: no protection; urgent (additional) vaccination is recommended, possibly combined with immunoglobulins
• 0.5 – 2.9 IU/ml: low protection; booster is recommended
• 3 – 10 IU/ml: good protection
• 10 IU/ml: very good protection

Sample retention period and timeframe for retesting (if sufficient sample is available): maximum 1 year

Purpose of the test

Titration of neutralizing antibodies against the rabies virus using the Rapid Fluorescent Foci Inhibition Test (RFFIT).

Criteria for performing this test as part of reference activities

• In case of diagnosis: clinical (encephalitis/myelitis) or epidemiological suspicion
• In case of vaccine monitoring: curative treatment (vaccination, possibly with immunoglobulins) after exposure to a potentially infected animal
• Monitoring vaccine immunity after a preventive vaccination is outside the scope of the reference center’s activities. In such cases, the test is billed to the requesting laboratory or hospital (€75.56/test).

Sample Instructions

• Type: Serum, blood in a sterile serum tube (without anticoagulants). For diagnostic purposes: paired sera with a 7–10 day interval.
• Storage and transport:
  • Store samples at 4°C after collection until transport
  • Transport chilled or at room temperature
  • In hermetically sealed container with triple packaging
  • Paired sera must be sent simultaneously
  • Sample stability: up to 2 weeks if kept below 37°C
• Minimum required volume for analysis: 0.5 ml (serum), 5 ml (blood)

Unacceptable Requests

This test has no diagnostic value for patients who have been exposed to a suspected animal but have not yet developed rabies symptoms. There is no seroconversion during the incubation period. Such individuals must be treated as soon as possible with a vaccine and possibly immunoglobulins. Contact the Institute of Tropical Medicine in Antwerp for this.

Turnaround Time (and Frequency of Testing)

• Turnaround time: 7 working days
• Testing days: Monday, Tuesday, Wednesday, Thursday

Reporting of Test Results and Pricing

• Test report will be sent within the maximum period, by post to the requesting lab or physician
• If non-conformity is found after receiving the sample (e.g., broken tube, insufficient volume, etc.) preventing the test from being carried out, the requester will be notified.
• Price: €75.56, billed to the requesting laboratory