Can Ticks Be Tested for Lyme Disease?
Ticks can be tested for Lyme disease and other tick-borne pathogens. Laboratories may analyze a removed tick for Borrelia burgdorferi, the bacterium responsible for Lyme disease. However, the accuracy of tick testing 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.
Learn more about the limitations of Lyme disease testing and diagnosis.
Can a Tick Be Tested After It Bites You?
Yes. Laboratories can test ticks for Lyme disease and other tick-borne pathogens using PCR techniques. However, results must be interpreted cautiously, particularly when the tick is engorged.
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 does not always reveal the true prevalence of Borrelia burgdorferi. Several explanations 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 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, non-engorged ticks are more likely to remain alive until DNA extraction, while engorged ticks may die 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 testing is not always reliable in determining your risk of infection.
If an engorged tick is removed and tested, it can be negative for Borrelia burgdorferi 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 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 important limitations.
When Tick Testing May Be Helpful:
- Confirms exposure to tick-borne pathogens in your region
- Identifies potential co-infections such as Babesia or Anaplasma
- Provides surveillance data for public health monitoring
- 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 DNA degradation
- Not all laboratories 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 infection.
When clinical suspicion is high based on symptoms or attachment duration, empirical antibiotic therapy may be warranted even when tick testing is negative.
Key Point
Ticks can be tested for Lyme disease, but testing results may be misleading—particularly when the tick is engorged. Negative results do not reliably exclude infection.
Clinical Insight
Ticks that feed long enough to become engorged are the most likely to transmit infection, yet they may be the least reliable specimens for laboratory testing. Clinical judgment and patient monitoring remain more important than tick testing results.
Frequently Asked Questions
Can ticks be tested for Lyme disease?
Yes. Ticks can be tested for Borrelia burgdorferi and other pathogens using PCR methods, though results must be interpreted cautiously.
Why do engorged ticks test negative more often?
Blood meal inhibitors, degradation of DNA, and tick death prior to testing may interfere with PCR detection.
Should I test a tick that bit me?
Tick testing can provide useful information but does not determine whether transmission occurred.
If my tick tests negative, am I safe?
No. A negative tick test does not rule out infection.
Should I wait for tick testing before treating symptoms?
No. Clinical decisions should be based on symptoms and exposure risk rather than tick testing results.
