How to read your Lyme test results
"Positive IgG, negative IgM — am I sick or not?" The lab report answers a precise question that nobody explains to you. Here's the translation: what each line measures, why timing decides what it means, and the questions worth bringing to your doctor.
1) Lyme testing is a two-tier system — a screening test, then a confirmation test — and you're only "positive" when both tiers agree. A positive first tier alone is not a diagnosis. 2) The test photographs your immune system, not the bacteria — and that camera is slow. IgM antibodies rise in the first weeks and stop being meaningful after about a month; IgG rises from roughly weeks 4–6 and then persists for years, even after successful treatment. That's why "positive IgG" so often means history, not activity — and why only the combination of result + symptoms + timing, read by a doctor, means anything at all.
Every week, someone posts a photo of their Lyme lab report to a forum with the caption "please help me read this." We've written about when to test and what the rash means; this page is the missing third piece — what the report says once it exists. One thing before any of it: this is translation help for a conversation with your doctor, not a substitute for one. The same line on two different people's reports can mean two different things, and the difference lives in clinical context we can't see from here.
What the lab actually did
A sensitive screening test for antibodies against Borrelia. Deliberately tuned to catch everything — which means it also catches look-alikes. Negative here = negative overall, done. Positive or equivocal → tier 2.
The specific test, reported as separate IgM and IgG results (the blot version lists individual "bands"). Since 2019 labs may run a second EIA instead — the "modified two-tier" — which is why some reports show no bands at all.
The clock behind the letters
IgM and IgG aren't two tests for the same thing — they're timestamps. IgM is the immune system's first responder; IgG is the long-term memory. Where you are on this clock changes what any result can mean:
Schematic, not to scale, and individual immune responses vary. The three practical takeaways: tests drawn in the first 2–3 weeks are frequently negative even in real infections (the window our timeline page warns about); IgM is only interpretable early — CDC guidance disregards IgM once an illness has lasted beyond about 30 days; and IgG persists for years after treatment, which is why there is no "test of cure."
The five reports people post, decoded
Too early to mean anything
This result is a photograph of a reaction that hasn't had time to develop — it neither clears you nor convicts the tick. The watch window and symptom checklist carry the next few weeks, and an expanding rash would be diagnosed on sight without any blood work.
Worth asking: "If symptoms appear, do we re-test, or treat on the clinical picture?"
A negative result wearing a scary first line
The screening tier is built to over-catch — viral infections, autoimmune conditions, and other bacteria can all trip it. The confirmation tier said no. Under the two-tier rule this is a negative overall, and a common one; it is not "a little bit positive."
Worth asking: "Given my symptoms, what else should we be looking at instead?"
The pattern that fits genuinely early Lyme
Early responder up, long memory not yet built — in someone with a recent bite or exposure and compatible symptoms, this is the textbook early-infection signature, and doctors treat it as such in context. The same pattern without any plausible exposure deserves more skepticism, which is the doctor's call to make.
Worth asking: "Does my exposure history and symptom timeline fit this result?"
The red flag most people read backwards
This looks alarming and usually isn't Lyme. By months into a real infection, IgG should have appeared; an isolated IgM that late is, per CDC guidance, not interpretable — and frequently a false positive. The honest translation: this result is more likely a testing artifact than late-breaking early Lyme.
Worth asking: "Should we disregard this IgM given how long I've had symptoms, and what explains them instead?"
The "confusing positive IgG" — antibody memory, needing context
The result behind half the forum posts. It can mean three different things: later-stage Lyme, if you have compatible current symptoms (certain joint, neurological, or heart presentations); past exposure — including an old infection your body or a forgotten course of antibiotics already resolved, since IgG persists for years; or occasionally cross-reaction from something unrelated. The lab value is identical in all three. Symptoms, history, and sometimes further workup are what separate them — there is no shortcut around that conversation.
Worth asking: "Which of these three does my clinical picture actually support — and if it's past exposure, does this result need any treatment at all?"
Band counting, briefly
If your tier 2 was a Western blot, the report lists individual protein "bands" — and this is where people drive themselves furthest into the night. The rules are thresholds, not vibes:
Two of three specific bands, and only within roughly the first 30 days of illness. One band present = negative.
Five of ten specific bands. Two or three reactive bands is a negative result — not a "weak positive," however it feels to read.
One band deserves its own sentence: 41 kDa is the flagellin band, and it reacts to tail proteins shared by many bacteria — including harmless ones. A lone 41 kDa band is one of the most common sources of false alarm on any blot report.
What no Lyme test can tell you
- Whether treatment worked. Antibodies persist for years after successful treatment, so serology is never a test of cure — recovery is judged by symptoms, not repeat blood work.
- New infection vs. old antibodies. A second tick bite in someone previously infected can't be confirmed or excluded by serology alone; the old positive muddies the water.
- Anything about STARI. The lone-star-tick rash illness mimics the Lyme rash and tests Lyme-negative — a negative result with a southern rash doesn't close the case.
- Infection during the early window. A negative in week one or two is an absence of evidence, not evidence of absence — which is why early Lyme is a clinical diagnosis.
A word on the specialty-lab report in your other tab
If you've been in these forums long, you've seen them: labs offering urine PCR panels, lymphocyte transformation tests, or in-house blot criteria that count bands the standard criteria don't. We understand exactly why they're tempting — they tend to return positives to people the standard tests told "no," and an answer, any answer, feels better than limbo. The honest position: results from tests that haven't passed FDA review shouldn't drive treatment decisions, and both the CDC and infectious-disease societies caution against them, because unvalidated positives lead to real harms — months of unnecessary antibiotics, and worse, the actual diagnosis going unhunted. Persistent symptoms are real and deserve a relentless workup. That's an argument for better tools, not looser ones.
Bring the actual lab printout, your symptom timeline, and your exposure story (when, where, what kind of tick if known) to a doctor — ideally one who sees tick-borne disease regularly. If any of these apply, make that appointment prompt:
- a positive two-tier result with current symptoms;
- an expanding rash at any point — that's treated on sight, test or no test;
- facial drooping, heart palpitations, shooting nerve pains, or marked joint swelling — later-stage signs that still respond well to treatment;
- results you and your doctor can't reconcile — a second opinion from an infectious-disease specialist is a normal next step, not an escalation.
Frequently asked
Does a positive IgG mean I have Lyme right now?
Not by itself. IgG persists for years — including after successful treatment — so a positive IgG can reflect later-stage Lyme (if symptoms fit), a past resolved exposure, or occasionally cross-reaction. The lab value is identical in all three cases; symptoms and history are what distinguish them, which makes this a clinical question rather than a lab question.
Why is my IgM positive six months after the bite?
Late isolated IgM positives are frequently false positives, and CDC guidance is to disregard IgM once illness has lasted beyond about 30 days — by then a real infection should show IgG. Ask your doctor directly whether your IgM result should be discounted on timing grounds; it's a known limitation, not a controversial question.
Should I retest after finishing antibiotics?
No — serology stays positive for years after successful treatment, so a repeat test can't tell you whether the bacteria are gone. Doctors track recovery by symptoms over weeks to months. A still-positive follow-up test is the expected outcome, not a treatment failure.
My blot shows two reactive IgG bands — is that "borderline"?
Under CDC criteria an IgG blot needs at least 5 of 10 bands; two bands is a negative result, full stop. And if one of them is the 41 kDa band, know that it's the least specific of all — it reacts to flagella shared across many common bacteria.
I'm sick, my tests are negative, and nobody has answers. What now?
If exposure was recent, timing may explain it — the first weeks are a known blind spot, and a rash would be diagnosed clinically anyway. If the illness is established and two-tier testing is negative, Lyme is genuinely unlikely, and the most useful next step is widening the search with your doctor rather than repeating Lyme tests. Your symptoms are real either way; the goal is the right diagnosis, not a particular one.