Can Ticks Be Tested for Lyme Disease?

Ticks can be tested for the Lyme disease bacteria and other tick-borne pathogens. But the accuracy of test results may depend on whether the tick is engorged.

A study by Gasmi et al. found that results may not be accurate when testing ticks which are engorged. The authors examined 4,596 I. scapularis (blacklegged) ticks removed from individuals living in Quebec.

They found that 24.9% of the non-engorged blacklegged ticks were infected with Borrelia burgdorferi, the causative agent of Lyme disease.

The Unexpected Finding: Engorged Ticks Test Lower

Engorged ticks were expected to have an even higher rate of infection with the Lyme disease bacteria. But the prevalence was much lower with only 8.9% of engorged ticks testing positive for the Lyme disease agent.

These findings are consistent with those from another Canadian study, suggesting this is a reproducible phenomenon rather than an isolated observation.

This counterintuitive result raises important questions about the reliability of tick testing as a diagnostic tool.

Why Do Engorged Ticks Test Negative?

It is still unclear why testing of engorged ticks is not accurately revealing the higher prevalence of Borrelia burgdorferi infection. Several theories have been proposed.

Blood Meal Inhibitors

The presence of inhibitors in the blood meal may interfere with DNA extraction and testing accuracy. Components of mammalian blood could affect the sensitivity of polymerase chain reaction (PCR) testing used to detect bacterial DNA.

Collection and Transportation Issues

Problems with the collection and transportation of engorged ticks may contribute to false negatives. Engorged ticks are more fragile and may degrade more quickly than non-engorged ticks.

Tick Viability

Perhaps the most straightforward explanation: engorged ticks may die during the interval between tick removal and laboratory testing. As Gasmi noted, un-engorged ticks are more likely to remain alive up to DNA extraction, while engorged ticks may well have died days or weeks before testing.

Dead ticks may yield degraded DNA samples that produce false negative results.

What This Means for Patients Who Find Ticks

A tick can be tested for Lyme disease, but it isn’t always a reliable tool in determining your risk of infection.

If an engorged tick is removed and tested, it can be negative for the Borrelia burgdorferi bacteria—even when the tick was actually infected and transmission may have occurred.

This creates a dangerous false reassurance. Patients who receive negative tick testing results may assume they are not at risk, when in fact the test simply failed to detect infection in an engorged tick.

Should You Test a Tick After a Bite?

Tick testing can provide useful information, but it has significant limitations.

When Tick Testing May Be Helpful:
– Confirms exposure to tick-borne pathogens in your area
– Identifies co-infections (Babesia, Anaplasma, Bartonella)
– Provides data for public health surveillance
– May support clinical diagnosis when positive

When Tick Testing Is Unreliable:
– Engorged ticks often test negative despite infection
– Negative results do not rule out transmission
– Testing delays may allow degradation
– Not all labs test for all pathogens

Most importantly, treatment decisions should not wait for tick testing results. If symptoms develop or the tick was attached for an extended period, clinical evaluation and empirical treatment may be appropriate regardless of tick testing outcomes.

Clinical Approach When a Tick Is Found

When a patient presents with a removed tick, the focus should be on clinical assessment rather than tick testing alone.

Consider the duration of attachment, the presence of symptoms, and the patient’s exposure history in an endemic area. Monitor for development of erythema migrans rash or systemic symptoms in the days and weeks following tick removal.

If tick testing is performed, interpret negative results cautiously—particularly if the tick was engorged. A negative tick test does not exclude the possibility of transmission or infection.

When clinical suspicion is high based on symptoms or attachment duration, empirical antibiotic therapy may be warranted even when tick testing is negative.

Frequently Asked Questions

Can ticks be tested for Lyme disease?
Yes, ticks can be tested for Borrelia burgdorferi and other tick-borne pathogens using PCR testing. However, accuracy varies based on tick engorgement status and testing conditions.

Why do engorged ticks test negative more often?
Engorged ticks may test negative due to blood meal inhibitors affecting DNA extraction, tick death before testing, or collection and transportation issues. Only 8.9% of engorged ticks tested positive compared to 24.9% of non-engorged ticks.

Should I test a tick that bit me?
Tick testing can provide useful information but has significant limitations. Negative results do not rule out infection, particularly if the tick was engorged. Clinical assessment and symptom monitoring are more important than tick testing results.

If my tick tests negative, am I safe?
No. A negative tick test does not guarantee you were not exposed to Lyme disease or other tick-borne infections. Engorged ticks frequently test negative despite being infected.

Should I wait for tick testing results before treating symptoms?
No. Treatment decisions should be based on clinical presentation, not tick testing results. If symptoms develop or attachment was prolonged, empirical treatment may be appropriate regardless of tick testing outcomes.

Clinical Takeaway

Tick testing for Lyme disease reveals an important paradox: the ticks most likely to transmit infection—those that fed long enough to become engorged—are the least likely to test positive. This finding has critical implications for patient care. A negative tick test cannot provide reassurance. It may simply reflect the technical limitations of testing engorged specimens rather than the absence of infection. Patients who submit engorged ticks for testing and receive negative results may be falsely reassured and delay seeking care when symptoms develop. This is why clinical judgment must guide care, not laboratory results from tick testing. When a patient presents with a tick bite, the focus should be on symptom monitoring, clinical assessment, and low threshold for empirical treatment—not waiting for tick testing results that may be falsely negative precisely when infection risk is highest.