Testing a child for Lyme disease involves a blood draw that checks for antibodies the immune system produces in response to the Lyme-causing bacteria. The standard approach uses two blood tests run in sequence, and the process is the same for children as for adults. Timing matters: antibodies typically take one to four weeks to develop after a tick bite, so testing too early can produce a false negative even when the infection is real.
The Two-Step Blood Test
The CDC recommends a two-tier testing process. The first step is a screening blood test called an enzyme immunoassay (EIA), which looks for antibodies against the Lyme bacteria. If this first test comes back negative, no further testing is needed. If it comes back positive or borderline, a second test is run on the same blood sample to confirm the result.
In the traditional version, that second test is a Western blot, which looks for antibodies reacting to specific proteins from the bacteria. For an early infection (symptoms present for 30 days or less), two out of three specific protein markers need to light up on the IgM portion of the blot. For a later-stage infection, at least five out of ten markers need to appear on the IgG portion. The overall result is only considered positive when both tiers are positive.
Many labs now use a newer approach called modified two-tier testing, which replaces the Western blot with a second, different EIA. This version catches about 10 to 20% more true positives during early infection compared to the traditional method, while maintaining the same rate of false positives. At later stages of disease, both approaches perform about equally well.
Why Timing Changes Everything
This is the single most important thing to understand about Lyme testing in children: the tests detect your child’s immune response, not the bacteria itself. In the first one to two weeks after infection, sensitivity ranges from roughly 35% to 60%, meaning the test misses a significant number of kids who actually have Lyme. The immune system simply hasn’t produced enough antibodies yet to register on the test.
If your child has a bull’s-eye rash (erythema migrans), most doctors will diagnose and treat Lyme based on that rash alone, without waiting for blood test results. The rash is considered reliable enough on its own, and waiting for antibodies to develop would only delay treatment. Blood testing becomes more important when there’s no rash but other symptoms point toward Lyme, or when symptoms suggest the infection has been present for weeks.
If a test comes back negative but your child’s symptoms persist and Lyme remains a concern, retesting in two to three weeks can catch antibodies that weren’t detectable the first time around.
Symptoms That Prompt Testing
In children, Lyme disease can look different depending on how far the infection has progressed. Early on, the telltale sign is the expanding red rash at the bite site, often with a clearing center. But not every child develops one, and kids may not notice or report a tick bite in the first place.
Beyond the rash, symptoms that should raise suspicion include fever, fatigue, headache, and muscle or joint aches. Joint swelling, particularly in the knees, is one of the more common later-stage presentations in children. Facial drooping (similar to Bell’s palsy) can appear on one or both sides of the face and is a hallmark of neurological Lyme in kids. Other neurological signs include numbness, tingling, shooting pain in the arms or legs, stiff neck, sensitivity to light, and severe headache. Some children develop these neurological symptoms within weeks of the initial infection.
When Spinal Fluid Testing Is Needed
If your child shows signs of neurological involvement, such as facial palsy, severe headaches with a stiff neck, or weakness in the limbs, the doctor may recommend a lumbar puncture (spinal tap) in addition to blood testing. This procedure collects a small amount of spinal fluid to look for inflammation and Lyme-specific antibodies produced within the nervous system.
The spinal fluid is checked for elevated white blood cell counts (particularly a type called lymphocytes), protein levels, and whether the body is making Lyme antibodies inside the central nervous system rather than just in the bloodstream. A confirmed diagnosis of neurological Lyme requires finding those locally produced antibodies in the spinal fluid or detecting the bacteria’s genetic material through a PCR test. This level of testing is only necessary when neurological symptoms are present. It’s not part of routine Lyme screening.
What Not to Test
If you found a tick on your child but they have no symptoms, guidelines from the Infectious Diseases Society of America recommend against running Lyme blood tests. Testing an asymptomatic child after a tick bite frequently produces misleading results, either false positives that trigger unnecessary treatment or false negatives that provide false reassurance.
Similarly, sending the tick itself to a lab for testing is not recommended for making treatment decisions. Even if the tick tests positive for Lyme bacteria, that doesn’t reliably predict whether your child will develop an infection. And a negative tick test doesn’t rule it out. Species identification of the tick can be useful (only blacklegged ticks transmit Lyme), but testing the tick for bacteria isn’t a substitute for monitoring your child for symptoms.
Co-infection Testing
Blacklegged ticks can carry more than just Lyme. The most common co-infection is anaplasmosis, which shows up in roughly 10% of Lyme patients. Babesiosis and other tick-borne illnesses occur less frequently but are worth knowing about. Anaplasmosis is treated with the same antibiotic used for Lyme, so your child would be covered for both even without separate testing. Babesiosis, a parasitic infection, requires different medication, so your doctor may order additional blood work if symptoms like high fever, chills, or anemia seem out of proportion to a typical Lyme presentation.
Some providers test for Bartonella or Mycoplasma alongside Lyme, but there is no evidence that ticks transmit these organisms. If your child’s doctor orders a broad “co-infection panel,” it’s worth asking which tests are supported by evidence for tick-borne transmission.
Understanding Your Child’s Results
A positive result on both tiers means your child has produced antibodies to the Lyme bacteria, which is consistent with an active or recent infection. Treatment decisions are based on this result combined with your child’s symptoms and exposure history.
One important nuance: IgG antibodies can remain detectable for months or even years after the infection has been successfully treated. A positive IgG result does not mean the infection is still active, and repeat testing should not be used to track whether treatment is working. Resolution of symptoms is what confirms successful treatment, not changes in antibody levels.
If your child tests positive for IgM antibodies (the type produced early in infection) but negative for IgG, and symptoms have been present for more than 30 days, the result should be interpreted cautiously. In that scenario, your doctor may recommend retesting in one to two weeks to see if IgG antibodies develop, which would confirm the diagnosis. Isolated IgM-positive results in patients sick for more than a month can sometimes be false positives.
A negative first-tier test generally means Lyme is unlikely, but if the blood was drawn within the first couple of weeks after a bite, a negative result doesn’t fully rule it out. The key question is always how long it’s been since the possible exposure and whether symptoms match.