Tick bite this summer: what can a blood test actually tell you?

Bitten this summer and feeling off now, what applies?

A tick bite in July that still nags at you in September is common. The first thing worth knowing: the vast majority of bites lead to no infection at all. The risk of developing Lyme disease after a single tick bite is around 2 percent.

Tiredness and generally feeling off in autumn have many possible explanations, and a tick bite two months ago is rarely the most likely one. Lyme disease usually causes more specific problems, above all a spreading redness around the bite site or clear nerve symptoms.

So the right first step is a review of your actual symptoms. If you have any of the signs described below, contact healthcare. If you have no symptoms at all, Swedish clinical practice holds that no test will help you, however recent the bite.

Which symptoms matter after a tick bite?

The most important sign is erythema migrans: a redness that grows in size around the bite site, often as a ring. It usually appears 1 to 4 weeks after the bite. No blood test is needed here at all. A doctor makes the diagnosis by looking at the redness and treats with antibiotics straight away. Taking an antibody test at that point can even mislead, since fewer than 50 percent have formed antibodies by the time the redness shows.

If the bacterium spreads in the body, other symptoms can follow, usually 2 to 6 weeks after the bite: facial paralysis, severe pain radiating into the arms or legs that is often worse at night, headache, neck stiffness or fever. By then the redness may already have faded.

Vague tiredness without any of these signs rarely points to Lyme disease. If you do seek care, it is the symptom picture that guides the workup.

What can a Lyme blood test show, and not show?

A Lyme blood test measures antibodies of the IgM and IgG type. A positive result shows that you have met the bacterium at some point, not that it is making you ill right now. That is the test's fundamental limitation, and there is no way around it.

The antibodies remain for years after a resolved infection, including one you never noticed. In southern and central Sweden roughly 5 to 10 percent of the population carry antibodies against Borrelia, the vast majority without being ill. A positive result without symptoms is therefore not grounds for treatment in Swedish care.

The test can also falsely reassure: early in an infection it is often negative. Serology has its place when a doctor suspects disseminated infection and interprets the result together with symptoms, sometimes alongside a spinal fluid sample. General inflammation markers such as CRP (a rapid measure of inflammation) and ESR (the sed rate) say nothing specific about Lyme disease.

Should you get tested after a bite without symptoms?

No. Swedish practice recommends neither blood tests nor preventive antibiotics after an uncomplicated tick bite. The reason is simple: a positive result without symptoms changes nothing, since it is not treated, and a negative result early after the bite rules nothing out.

What you should actually do is remove the tick as soon as possible with tweezers or a tick remover close to the skin, then keep an eye on the bite site for a few weeks. If a clear spreading redness appears, or symptoms such as fever and headache, contact healthcare.

Enkel Health does not offer tests for Borrelia or TBE today. The advice above does not depend on that: after a bite without symptoms there is no blood test, from us or anywhere else, that gives you a useful answer.

What about TBE, can a blood test show infection or protection?

TBE is a virus, not a bacterium, and the logic differs. When TBE is suspected in someone with symptoms, such as fever and severe headache, healthcare does use blood tests: the diagnosis is made by detecting antibodies against the TBE virus in blood, sometimes alongside a spinal fluid sample. There is no curative treatment; the infection resolves on its own and care is aimed at the symptoms.

Protection against TBE comes from the vaccine. The Public Health Agency of Sweden recommends vaccination for adults and children from age 3 who risk tick bites in risk area 1, the areas where the risk of infection is highest.

A blood test after a bite without symptoms does not help here either. The same goes for the question of whether your vaccine has given protection: antibody testing is not how protection is assessed in routine care. Follow the vaccination schedule instead, and check with healthcare if you are unsure about your doses.

When should you seek care right away?

Contact a primary care centre if any of this applies:

1. A redness around the bite site that keeps growing, no matter how long ago the bite was. 2. Fever, headache or marked tiredness in the weeks after a bite. 3. Pain radiating into the arms or legs, especially if it is worse at night.

Seek urgent care, calling 112 if needed, if you develop:

1. Severe headache with a stiff neck. 2. Facial paralysis, for example one corner of the mouth drooping. 3. High fever and feeling seriously unwell.

If in doubt, call 1177 for advice. Lyme disease is treated effectively with antibiotics once a doctor has made the diagnosis, which is exactly why symptoms should be assessed by healthcare rather than monitored with tests on your own.

This article is general health information, not medical advice and not an assessment of your values. If you have symptoms or concerns, contact your healthcare provider.