Explanation

Borrelia IgG antibodies (Lyme disease): what is measured?

Lyme disease is caused by the Borrelia bacterium, which is transmitted through a tick bite. This test measures whether your blood contains IgG antibodies against that bacterium. IgG is the antibody the immune system makes later, usually a few weeks to months after infection, and it then often remains detectable for years. According to the CBO guideline on Lyme disease, testing takes place in two steps: first this screening test (an EIA), and with a positive or doubtful result an immunoblot on the same blood sample as confirmation.

What can it detect?

Antibodies that fit Lyme disease that has been causing symptoms for some time, such as Lyme arthritis (swollen knee), nerve symptoms or the skin condition acrodermatitis
A past Borrelia infection, even if it caused no symptoms

Result

What does the result mean?

Positive result

A positive screening test means that IgG antibodies were found, so your immune system has had contact with the Borrelia bacterium at some point. On its own, this is not proof of Lyme disease: according to the guideline, the result must be confirmed with an immunoblot, and only then is it assessed together with the symptoms. About 5 to 10 in 100 healthy Dutch people have these antibodies without being ill, and in people who work outdoors a lot this is more common. With long-lasting vague symptoms without signs that clearly fit Lyme disease, the chance of a false-positive result is very high, according to the LCI guideline (RIVM).

Negative result

A negative result means that no IgG antibodies were found. With symptoms that have been present for more than 8 weeks, this makes Lyme disease very unlikely, because at that stage almost everyone with Lyme disease has IgG antibodies. In the first weeks after infection, IgG is often not yet detectable; the test can then be repeated after 4 to 8 weeks. With a typical red ring or spot after a tick bite, a negative result says little: at that early stage, the test finds about half of the infections.

After an abnormal result

With a positive or doubtful result, the GP has an immunoblot done on the same blood sample and assesses the result together with the symptoms; with symptoms of the nerves, joints or heart, referral to hospital usually follows. With symptoms of short duration and a negative result, the test can be repeated after 4 to 8 weeks. Lyme disease is not notifiable in the Netherlands.

Reliability

How reliable is the test?

According to the CBO guideline on Lyme disease, this is the first step of two-step testing: a positive or doubtful screening test is confirmed with an immunoblot on the same sample. In Lyme disease that has been causing symptoms for more than 8 weeks, the sensitivity of serology is close to 100 percent, so it is mainly a negative result that is meaningful. In an early infection with a red ring or spot, the sensitivity is about 50 percent, so the test then misses half of the infections. How much a positive result says depends strongly on how likely Lyme disease already was beforehand; in people without matching signs, it says little.

What can affect the result?

IgG antibodies often remain detectable for years to a lifetime after a past or treated infection and then say nothing about an active infection.
In the first weeks after infection, the test can be negative even though there is an infection (window period).
Cross-reactions occur, among others with other infections and with autoimmune diseases; that is why the immunoblot is needed as confirmation.
Antibodies are not suitable for checking the effect of a course of antibiotics: they fall just as much in people with and without lasting symptoms.

Who it is for

Who is the test useful for?

Useful for

Useful with symptoms that fit Lyme disease and have been present for a few weeks, such as a swollen knee without a clear cause, radiating nerve pain, paralysis of one side of the face or a bluish-red, thin skin change on an arm or leg. Not useful with a typical red ring or spot after a tick bite: that is a clinical diagnosis and the test is not sensitive enough for it. Also not useful after a tick bite without symptoms, as a check after treatment, or as a general check in people without symptoms, because antibodies then often occur without disease.

How common is it?

In the Netherlands, people together get about 1.5 million tick bites a year and about 27,000 people a year get Lyme disease. By far most of them only have a red ring or spot; about 1,500 people a year get symptoms of the joints, skin, nerves or, very occasionally, the heart. About 5 to 10 in 100 healthy Dutch people have antibodies against Borrelia without active disease.

RIVM and the RIVM/LCI guideline on Lyme disease

Drawbacks and risks

Antibodies also occur in healthy people; without matching symptoms, a positive result can lead to an incorrect diagnosis of Lyme disease and unnecessary antibiotic use.
A positive screening test without a confirming immunoblot can cause unnecessary worry, while the result does not yet say anything.

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