Lyme Disease Blood Test: How to Read the Result

The Lyme disease blood test looks for antibodies to Borrelia after a tick bite. Learn how two-tier testing works, why it can be falsely negative or positive, and how a doctor interprets it.

Published July 20, 202611 min readWritten by the Blood Analysis Team · Reviewed and verified by Julien Priour

The Lyme disease blood test looks for antibodies in your blood against Borrelia, the bacterium spread by an infected tick bite. It's a useful test, but a widely misunderstood one: it is not for everyone, it is not the right test at the very start of illness, and a positive result does not by itself prove an active infection. This guide explains what the test is for, how two-tier testing works, why it can be falsely negative or falsely positive, and how your clinician interprets it — always alongside your symptoms. It belongs to the broader family of infection and serology tests.

Key takeaways

Lyme disease is an infection caused by the bacterium Borrelia, spread by an infected tick bite; the classic early sign is an expanding rash called erythema migrans.¹²
⚠️ Erythema migrans is diagnosed clinically, by sight — at that stage you do NOT need a blood test, because antibodies are often not detectable yet, and antibiotics are started on the exam alone.³⁴
The blood test is most useful for disseminated Lyme (neurologic, joint, or heart involvement) that appears without a recognized erythema migrans.¹⁵
It is done in two tiers: a sensitive ELISA/EIA screen first, then — if positive or equivocal — a confirmatory Western blot / immunoblot (more specific).⁵¹
Antibodies take weeks to appear (so early tests can be falsely negative), and IgG persists for years after cure: a positive result does not necessarily mean a current infection.⁵⁴
⚠️ Beware over-testing and unvalidated "specialty lab" tests, which produce many false positives. Only your clinician interprets the result together with your symptoms.³⁴

What is the Lyme disease test?

Lyme disease (Lyme borreliosis) is a bacterial infection caused by bacteria in the Borrelia burgdorferi group. It spreads to people through the bite of an infected tick (mostly spring through fall, in wooded and grassy areas). Most tick bites do not transmit the disease.¹²

After infection, the immune system makes antibodies against the bacteria — first IgM (an early response), then IgG (later and longer-lasting). The Lyme disease blood test does not detect the bacterium itself; it detects these antibodies. That makes it indirect evidence of contact with Borrelia — which is exactly why interpreting it takes care.⁵¹

Serology is not a direct test for the bacterium. Lyme is almost never diagnosed by culture or PCR in routine practice, because the organism is hard to culture. So we rely on antibodies — and it's essential to know when they are trustworthy and when they are not.⁵

Why the test is done

A crucial, often-misunderstood point: the blood test is not ordered for erythema migrans. Erythema migrans — the expanding red rash, often circular, that appears at the bite site over days to weeks — is the hallmark of early localized Lyme. It is diagnosed clinically, on exam, and antibiotics are started without waiting for serology, because at this stage antibodies often haven't appeared yet (a blood test would be falsely reassuring).³⁴

The test becomes useful for disseminated, later disease that shows up without a recognized erythema migrans:¹⁵

neurologic Lyme (Lyme neuroborreliosis: facial palsy, meningitis, radicular pain);
joint disease (Lyme arthritis, often a swollen knee);
heart involvement (Lyme carditis, conduction block);
late skin disease (acrodermatitis chronica atrophicans, mostly in Europe).

In these situations antibodies have had time to develop, so serology is expected to be positive. Conversely, the test is not a screening tool to run "just in case" after a simple tick bite, or for isolated fatigue with no other sign: in that setting it mostly yields false positives and anxiety.³⁴

Do you need to fast?

No. The Lyme disease test is a simple venous blood draw that requires no fasting — you can eat normally beforehand, and no special preparation is needed. If other tests are ordered on the same requisition, follow the strictest instruction (see Do you need to fast before a blood test?).⁶

How to read the result

Lyme serology is not a number to compare against a "normal value." It's a qualitative test (positive / equivocal / negative) read in two tiers, in a set order. This is the official recommendation in the United States (CDC) and Europe alike.¹³⁵

Tier	Test	Role
Tier 1 (screen)	ELISA / EIA	A sensitive test that shouldn't miss true cases. If negative → stop (no tier 2). If positive or equivocal → confirm.
Tier 2 (confirm)	Western blot / immunoblot (IgM and/or IgG)	A more specific test: confirms the antibodies really target Borrelia and weeds out tier-1 false positives.

Serology is only considered positive when both tiers are positive. A positive ELISA alone, without confirmation, is not enough.¹⁵

What's new: the "modified two-tier" (EIA-EIA) algorithm. Since 2019, the U.S. CDC has cleared an alternative in which the Western blot is replaced by a second ELISA (two EIAs run in sequence). This modified two-tier testing is easier to automate and performs at least as well as the classic Western blot, with better early sensitivity in several studies.¹⁷⁸

Two limits to always keep in mind:

Antibodies take weeks to appear. In the first weeks after a bite, serology can be falsely negative even though infection is present. That's why we never rely on an early test to rule out early Lyme — and why erythema migrans is treated without serology.⁵⁴
IgG persists for a long time. After treated, cured infection, IgG antibodies stay detectable for months or years. A positive test may simply reflect past contact with the bacterium, not active infection. You also don't "follow" a cured Lyme with repeat serologies: the result doesn't necessarily fall.⁵⁴

Understanding your results

A positive result

A test positive on both tiers means your body has encountered Borrelia. But — this is the key point — it does not by itself tell you whether the infection is active, old, or cured. Interpretation depends entirely on the clinical picture:³⁵⁴

a positive test with a suggestive picture (arthritis, facial palsy, meningitis…) supports Lyme disease and guides treatment;
a positive test with no suggestive symptoms does not prove active Lyme: it may reflect past contact (IgG persists) or be a false positive (cross-reaction with other infections). It does not, on its own, justify antibiotics.

That's why testing "just in case" in someone without suggestive signs mostly creates confusion. The result is always read with a clinician, factoring in exposure, symptoms, and their timing.

A negative result

A negative test usually means no Borrelia infection — except at the very start: in the first weeks, antibodies may be absent (a false negative). When early Lyme is strongly suspected, a clinician may repeat the test a few weeks later (a "convalescent" sample) to catch antibodies as they rise.⁵³

On the other hand, a negative test is strong evidence against Lyme when symptoms have lasted months or years: by then, true Lyme borreliosis would almost always be seropositive. A negative test in that setting is a cue to look for another cause of the symptoms.⁴³

The "chronic Lyme" question: staying with the evidence

This is a sensitive topic that deserves honesty and respect. Some people are left, after appropriate treatment, with real and sometimes disabling symptoms — fatigue, pain, trouble concentrating. Clinicians recognize this as post-treatment Lyme disease syndrome (PTLDS). These symptoms are real and deserve care and attention.⁴

At the same time, the evidence does not support some common practices:

prolonged courses of antibiotics (for months) have not shown benefit in randomized trials and carry real risks;⁴³
unvalidated tests offered by some "specialty" labs (non-standardized serologies, lymphocyte transformation tests, and the like) produce many false positives and should not be used to make the diagnosis;³⁴
a positive test does not automatically explain chronic symptoms: pinning every lasting fatigue on "chronic Lyme" risks missing another, treatable diagnosis.³

The goal isn't to minimize anyone's suffering — it's to stay grounded in evidence so as not to feed false promises. The path forward is built with a clinician, keeping an open mind about the cause.

What affects your Lyme test

Several things shape how the test reads: the time since the bite (too early = false negative), early antibiotic treatment (which can blunt the antibody response), and especially cross-reactions — other infections (other spirochetes such as syphilis, some viral infections, mononucleosis, sometimes autoimmune disease) can make the ELISA falsely positive, which is exactly why the tier-2 confirmation exists.⁵¹ The Lyme test is often ordered alongside others: an inflammation marker such as CRP, and sometimes other infection and serology tests to work up a febrile or neurologic picture. Always report your symptoms, when they started, and any known tick bite: that context is what gives the result meaning.

Recent research

According to recent PubMed-indexed publications:

The modified two-tier (EIA-EIA) algorithm is spreading. Cleared by the CDC in 2019, it replaces the Western blot with a second ELISA. Independent studies confirm it is at least as reliable as the classic approach, with better early sensitivity — including in European patients with erythema migrans.⁷⁸
Performance depends heavily on stage. A multicenter study shows serology is poorly sensitive at the erythema-migrans stage (hence the clinical diagnosis there) but almost always positive in disseminated disease (neuroborreliosis, arthritis); it also notes that routinely adding IgM mainly increases false positives.⁹⁵
A vaccine in clinical trials. The candidate vaccine VLA15 (targeting Borrelia's OspA protein) showed good immunogenicity and acceptable tolerability in a phase 2 trial across adults, adolescents, and children — a prevention strategy now under evaluation (trial NCT04801420).¹⁰¹¹
The debate over persistent symptoms (PTLDS) remains active. Recent reviews confirm that ongoing active infection has not been demonstrated as the cause of PTLDS in humans, and that prolonged antibiotics provide no benefit — steering research toward other mechanisms.⁴

These findings concern diagnosis and research; they do not authorize self-medication and do not replace your physician's advice.

Get your Lyme disease test interpreted by AI DiagMe

A Lyme result is never read alone: its meaning depends on your symptoms, the time since the bite, the stage of illness, and other tests (CRP, other infection and serology tests). That cross-reading is what tells an active infection apart from a distant past exposure.

👉 AI DiagMe interprets your lab results — blood, urine, or stool — in plain language, taking your whole profile into account. An informational service that does not provide a diagnosis and complements, never replaces, your physician.

Frequently asked questions

Should I get a Lyme test after a tick bite?

No, not routinely. A tick bite does not call for an immediate blood test: too early, it would be falsely negative. The right steps are to remove the tick promptly, watch the area for a few weeks, and see a clinician if an expanding red rash appears (erythema migrans) or symptoms develop.¹²

What does a positive Lyme test mean?

That your body has encountered Borrelia. It does not by itself say whether the infection is active, old, or cured — IgG persists for years. A positive test with suggestive symptoms supports the diagnosis; without symptoms, it doesn't prove active Lyme. Only a clinician interprets it with the clinical picture.⁵³

Does a negative test rule out Lyme disease?

Usually yes — except at the very start, when antibodies may be absent (false negative). But a negative test is strong evidence against Lyme when symptoms have lasted for months: by then, true Lyme would almost always be positive.⁵⁴

Why isn't serology done for erythema migrans?

Because erythema migrans is diagnosed clinically, by sight, and at that early stage serology is often still negative. Antibiotics are started without waiting for the lab. Testing here would risk falsely reassuring you.³⁴

What is "two-tier" testing (ELISA then Western blot)?

A highly sensitive ELISA/EIA screen acts as the first filter. If it's positive or equivocal, a more specific Western blot / immunoblot confirms. Serology is positive only when both are. A newer variant (CDC-cleared) replaces the Western blot with a second ELISA.¹⁵

Is there such a thing as "chronic Lyme"? Do I need long-term antibiotics?

Some people have real, lasting symptoms after treatment — this is recognized as post-treatment Lyme disease syndrome (PTLDS). However, prolonged antibiotic courses have not shown benefit in trials and carry risks. The way forward is built with a clinician, without relying on unvalidated tests.⁴³

Can I trust "Lyme specialty lab" tests?

Be cautious. Unvalidated tests (non-standardized serologies, cellular tests, and so on) produce many false positives and are not recommended for diagnosis. Rely on validated testing (ELISA plus confirmation) interpreted by a clinician.³⁴

Is a Lyme test a cancer marker?

No. It only looks for antibodies against a bacterium. It has nothing to do with cancer screening.

The bottom line

The Lyme disease blood test looks for antibodies against the bacterium Borrelia — it's not a number but a qualitative, two-tier test (an ELISA screen, then a Western blot or a second ELISA to confirm). Keep the essentials in mind: it's not done for erythema migrans (a clinical diagnosis, treated right away); it's most useful for disseminated disease; it can be falsely negative early (antibodies lag) and IgG persists after cure (positive ≠ active infection). Be wary of over-testing and unvalidated tests. PTLDS is real, but prolonged antibiotics have not proven beneficial. No serology is read alone — it's your whole symptom picture and context that counts, which is what AI DiagMe provides, alongside your physician.

Sources

Official U.S. sources and peer-reviewed publications (PubMed, ClinicalTrials.gov) used for this guide:

Centers for Disease Control and Prevention (CDC) — Lyme Disease: Diagnosis and Testing (two-tier serologic testing). cdc.gov ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹²
Mayo Clinic — Lyme disease: Diagnosis & treatment. mayoclinic.org ↩ ↩² ↩³
Infectious Diseases Society of America (IDSA), AAN & ACR — Clinical Practice Guidelines for the Prevention, Diagnosis and Treatment of Lyme Disease (2020). idsociety.org ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵
Kullberg BJ, Vrijmoeth HD, van de Schoor F, Hovius JW. Lyme borreliosis: diagnosis and management. BMJ, 2020. PubMed · DOI ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷
Branda JA, Steere AC. Laboratory Diagnosis of Lyme Borreliosis. Clin Microbiol Rev, 2021. PubMed · DOI ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷
MedlinePlus (U.S. National Library of Medicine, NIH) — Lyme Disease Tests. medlineplus.gov ↩
Landry ML, Hassan S, Rottmann BG, et al. Performance of two modified two-tier algorithms for the serologic diagnosis of Lyme disease. J Clin Microbiol, 2024. PubMed · DOI ↩ ↩²
Baarsma ME, Schellekens JFP, Meijer BC, et al. Diagnostic parameters of modified two-tier testing in European patients with early Lyme disease. Eur J Clin Microbiol Infect Dis, 2020. PubMed · DOI ↩ ↩²
Hoeve-Bakker BJA, Jonker M, Brandenburg AH, et al. The Performance of Nine Commercial Serological Screening Assays for the Diagnosis of Lyme Borreliosis: a Multicenter Modified Two-Gate Design Study. Microbiol Spectr, 2022. PubMed · DOI ↩
Wagner L, Obersriebnig M, Kadlecek V, et al. Immunogenicity and safety of different immunisation schedules of the VLA15 Lyme borreliosis vaccine candidate in adults, adolescents, and children: a randomised, observer-blind, placebo-controlled, phase 2 trial. Lancet Infect Dis, 2025. PubMed · DOI ↩
ClinicalTrials.gov — A Study to Evaluate Different Immunization Schedules of VLA15 in Healthy Participants (Lyme borreliosis vaccine). Identifier NCT04801420. clinicaltrials.gov ↩