TBE IgG (Tick-borne Encephalitis): Guide

What are tick-borne encephalitis IgG antibodies

Tick-borne encephalitis (TBE) IgG antibodies are proteins produced by the immune system after contact with the tick-borne encephalitis virus or after vaccination. IgG-class antibodies appear later than IgM and persist for a long time, sometimes for life. The purpose of this test is to determine whether a person has been exposed to the virus or whether a vaccine has produced a protective immune response.

The test is most commonly performed using the ELISA method from a venous blood sample. The result is expressed in VIEU/mL or U/mL units. The specific positive result threshold depends on the laboratory's test kit.

Reference ranges

The TBE IgG test is qualitative or semi-quantitative — the result is classified as negative, equivocal, or positive based on the laboratory's stated cutoff value. There are no universal numerical norms, as each manufacturer's kit has its own cutoff values. It is important to follow the specific laboratory's guidelines.

When might the result be positive

• After a past tick-borne encephalitis infection — antibodies can persist for years or decades.
• After TBE vaccination — the vaccine stimulates IgG production.
• Cross-reactions — rare, but possible with other flaviviruses.

A positive IgG result by itself does not indicate an active infection. It shows that the immune system has encountered the virus or a vaccine antigen at some point.

When might the result be negative

• The person has not been exposed to the TBE virus and has not been vaccinated.
• The test was performed too early after infection — IgG antibodies typically appear 2–4 weeks after symptom onset.
• Immunosuppression — in some cases the immune system does not produce a sufficient quantity of antibodies.

What to do with the results

If the test was performed because of suspected infection, it is important to evaluate IgG together with IgM antibodies. Positive IgM with negative IgG suggests a possible early infection stage. Both positive — may indicate a recently resolved or active-response phase. Positive IgG without IgM — past infection or vaccination.

In equivocal cases, the doctor may recommend repeating the test after 2–3 weeks and monitoring antibody dynamics.

Monitoring over time

If you are being vaccinated against TBE, the IgG test can show whether the vaccine has produced an immune response. After a complete vaccination course, IgG is typically detectable. Timely booster doses help maintain protective levels.

Questions for your doctor

1. Does my IgG result indicate a past infection or a vaccination effect? 2. Should IgM antibodies also be tested to rule out infection? 3. When should I have a repeat test if my result is equivocal? 4. Is my vaccination schedule sufficient for protection against tick-borne encephalitis?