Lyme Disease Testing: Why the Results Confuse People

Few test results generate as much argument as a Lyme disease test. People are told they are negative and do not believe it. People are told they are positive years after treatment and think the infection never left. Both reactions come from the same misunderstanding about what the test actually measures.

It does not look for the bacteria. It looks for your immune system’s response to them — and antibodies behave differently from the thing that caused them.

Two consequences of testing for antibodies

Almost every confusing Lyme result follows from one of two facts.

• Antibodies take time to appear. In the first couple of weeks after infection, the test is often negative even though the infection is real. Testing too early is the single most common cause of a falsely reassuring result.
• Antibodies persist afterwards. They can remain detectable for years after successful treatment. A positive test months or years later does not mean the infection is still active, and it is not a way to check whether treatment worked.

What two-tier testing means

Standard testing runs in two steps. The first is a sensitive screening test, designed to miss as few true cases as possible, which means it produces some false positives. The second is a more specific test run only on samples that screened positive, to sort the true from the false.

How to read a two-tier result

Result	What it means	What follows
First test negative	Testing stops here	Lyme unlikely, unless it is very early — repeat if symptoms began recently
First positive, second negative	The screen was a false positive	Reported negative overall; no treatment for Lyme
Both positive	Antibodies confirmed	Interpreted with your symptoms and exposure, not alone
Positive after past treatment	Antibodies persisting	Expected; not evidence of ongoing infection
Positive, no symptoms, no exposure	Possible false positive	Usually not treated on the result alone

That third row is where clinical judgment enters. A positive test in someone with a plausible exposure and matching symptoms means something quite different from the same result in someone with neither.

The rash is better evidence than the blood test

The expanding rash that can follow a bite — often but not always ring-shaped, growing over days, usually not itchy or painful — is diagnostic on sight. If it is present and typical, treatment starts without waiting for serology, because the test is frequently negative at that stage.

Not everyone gets it, and it is missed easily on the back or scalp, or on darker skin where the redness is harder to see. Its absence proves nothing. Our article on tick bites in Georgia covers the other tick-borne illnesses in this region, several of which are more common here than Lyme.

Treatment, and what it does and does not resolve

Early Lyme disease is treated with a short course of oral antibiotics — typically two to three weeks — and the great majority of people recover fully. Later manifestations affecting joints, the nervous system or the heart are treated for longer, sometimes intravenously.

A minority of people have symptoms that persist for months after treatment: fatigue, aches, difficulty concentrating. Those symptoms are real, and they are recognized. What repeated studies have not supported is that they are caused by ongoing infection or improved by extended courses of antibiotics — which carry their own harms, as our articles on antibiotic duration and C. difficile describe.

That is an uncomfortable answer, because it acknowledges the symptoms without offering a simple fix. It is also the honest one, and it is why persistent symptoms after Lyme are worth a proper assessment rather than an assumption in either direction.

Geography is part of the interpretation too. Lyme is concentrated in the Northeast, the mid-Atlantic and the upper Midwest, and is far less commonly acquired in Georgia than the tick-borne illnesses covered in our article on what Georgia ticks carry. A positive result in someone who has never left the Southeast is read more cautiously than the same result after a summer in Connecticut — which is exactly the kind of context a test result alone cannot supply.

After a tick bite, before any test

1. Remove the tick promptly with fine-tipped tweezers, gripping close to the skin and pulling steadily upward
2. Do not burn it, smother it, or twist it
3. Wash the area and your hands
4. Note the date; the timing matters far more than the tick itself
5. Watch the site for an expanding rash over the following weeks
6. Do not send the tick for testing — a positive tick does not mean you were infected
7. Seek advice about a single preventive antibiotic dose, which is considered in specific circumstances and only within 72 hours

Testing everyone who has been bitten is not recommended. Most bites do not transmit anything, and a test taken immediately after a bite reflects your status before it.

When to seek an opinion

• An expanding rash after a known or possible tick bite
• Fever, headache and aches in the weeks after outdoor exposure; see fever and where you have been
• A swollen, painful joint — the knee is the classic one — weeks to months later
• Facial weakness on one side, or new numbness or tingling
• Palpitations, breathlessness or fainting, which can indicate heart involvement
• Persistent symptoms after treatment, which deserve assessment rather than repeated courses

Interpreting equivocal serology, and sorting out symptoms after treatment, is something an infectious disease practice does regularly. Our article on when to see an infectious disease specialist explains what that involves, and you can reach us through the contact page.

Frequently asked questions