What is the test called for a tick bite?

Initial Assessment After a Tick Encounter

Risk Factors and Transmission Probability

The diagnostic evaluation after a tick exposure relies on serologic testing for Borrelia burgdorferi, most commonly a two‑tier approach: an enzyme‑linked immunosorbent assay (ELISA) screened by a Western blot confirmation. In some settings, polymerase chain reaction (PCR) on blood or tissue samples is added to detect early infection when antibodies are absent.

Risk factors that increase the likelihood of a positive result include:

Tick species known to transmit Borrelia (e.g., Ixodes scapularis in North America, Ixodes ricinus in Europe).
Attachment duration exceeding 24–36 hours, with transmission probability rising sharply after 48 hours.
Nymphal stage of the tick, which is small and more likely to remain unnoticed.
Geographic regions with established endemic foci.
Outdoor activity during peak tick season (late spring to early autumn).
Host factors such as immunosuppression or previous lack of prophylactic antibiotics.

Transmission probability is not uniform. Studies estimate that a fully engorged nymph can transmit Borrelia to a human in approximately 30–50 % of bites lasting more than 48 hours, whereas the risk drops below 5 % for removal within the first 24 hours. Adult ticks, although larger, generally have a lower infection rate but can still transmit the pathogen if attached long enough. Seasonal variation further modifies risk, with the highest probabilities observed in midsummer when tick activity peaks.

Clinical Surveillance and Symptom Monitoring

Clinical surveillance after a tick exposure relies on systematic observation of the patient’s condition and timely identification of emerging signs. Health professionals record the bite site, note the tick’s identification when possible, and schedule follow‑up appointments at defined intervals (e.g., 2, 4, and 8 weeks). Documentation includes temperature, rash appearance, joint pain, and neurologic complaints, enabling early detection of infections such as Lyme disease or anaplasmosis.

The diagnostic assay most frequently ordered for suspected tick‑borne illness is a two‑tier serologic evaluation. Initial screening employs an enzyme‑linked immunosorbent assay (ELISA) to detect antibodies, followed by a confirmatory Western blot if the ELISA result is positive. In cases where early infection is suspected and antibodies may be absent, polymerase chain reaction (PCR) testing of blood or tissue samples provides direct detection of pathogen DNA.

Key components of symptom monitoring:

Daily measurement of body temperature and documentation of fever spikes.
Visual inspection of the bite area for expanding erythema or target‑shaped lesions.
Assessment of joint stiffness or swelling, particularly in the knees and wrists.
Inquiry about fatigue, headache, or neurological disturbances such as facial palsy.

Prompt reporting of any abnormal findings to the treating clinician triggers immediate laboratory testing and, if necessary, initiation of antimicrobial therapy. Continuous surveillance ensures that treatment decisions are based on objective clinical evidence rather than speculation.

The Challenge of Early-Stage Diagnosis

Early-stage diagnosis after a tick bite confronts clinicians with limited biological signals. Within the first weeks, pathogen load is often low, and the host’s immune response has not produced detectable antibodies. Consequently, conventional serologic assays yield false‑negative results, forcing reliance on alternative methods.

Key obstacles include:

Timing of specimen collection – molecular techniques require fresh tissue or blood drawn before the pathogen disseminates; delayed sampling reduces nucleic‑acid concentration.
Test sensitivity – polymerase chain reaction (PCR) can identify Borrelia DNA at low levels, yet assay performance varies with primer design and laboratory proficiency.
Sample type – skin biopsies from the erythema migrans lesion provide higher pathogen yield than peripheral blood, but invasive collection limits routine use.
Cross‑reactivity – immunoassays such as ELISA may react with unrelated spirochetes, leading to ambiguous results without confirmatory Western blot.

The diagnostic pathway typically proceeds as follows:

Clinical assessment – identification of characteristic rash, exposure history, and symptom onset.
Molecular detection – PCR targeting specific gene regions (e.g., flaB, ospA) performed on lesion biopsy or early blood draw.
Serologic testing – ELISA screening followed by confirmatory immunoblot if sufficient time has elapsed for antibody development.

Effective early detection hinges on prompt specimen acquisition, selection of high‑sensitivity molecular assays, and integration of clinical judgment with laboratory data.

Serological Diagnostic Protocols for Borreliosis

The Standard Two-Step Testing Strategy

Tier One Screening: «Enzyme Immunoassay» («EIA»)

Enzyme Immunoassay (EIA) serves as the initial, tier‑one screening method for detecting infection after a tick bite. The assay measures antibodies that target specific antigens of the pathogen transmitted by the tick, most commonly Borrelia burgdorferi, the causative agent of Lyme disease.

The procedure involves coating a microtiter plate with recombinant antigens, adding patient serum, and allowing any specific antibodies to bind. A secondary enzyme‑linked antibody recognizes bound antibodies; the addition of a substrate produces a measurable color change. The intensity of the color correlates with antibody concentration, providing a quantitative result.

Key characteristics of the tier‑one EIA:

High sensitivity, reducing the chance of missing early infections.
Automated platforms enable rapid processing of multiple samples.
Results expressed as optical density values with established cutoff thresholds for positive, negative, and equivocal outcomes.

Interpretation guidelines:

Positive result → proceed to tier‑two testing (Western blot) for confirmation.
Negative result → unlikely current infection; repeat testing may be warranted if clinical suspicion persists.
Equivocal result → repeat the assay after a defined interval or advance to confirmatory testing.

Limitations include possible cross‑reactivity with antibodies from other spirochetal infections and reduced sensitivity during the first few weeks post‑exposure. Nonetheless, EIA remains the standard first‑line assay for evaluating patients who present after a tick bite.

Tier Two Confirmation: The «Western Blot» Assay

The Western blot assay serves as the second‑tier test used to confirm the presence of antibodies against Borrelia burgdorferi after an initial screening result. It detects specific protein bands on a nitrocellulose membrane, each representing a distinct antigenic component of the spirochete. A positive result requires the identification of a predefined combination of bands, typically including OspC (22 kDa), p41 (flagellin), and one or more of the following: p100, p39, p58, p83, or p93. The assay distinguishes true infection from cross‑reactive antibodies that may cause false‑positive screening outcomes.

Sample collection involves venous blood drawn into serum separator tubes. After clotting and centrifugation, serum is applied to the blot. Proteins are separated by electrophoresis, transferred onto the membrane, and probed with patient serum. Bound IgM and IgG antibodies are visualized using enzyme‑linked secondary antibodies and a chromogenic substrate.

Interpretation follows CDC‑recommended criteria:

IgM: at least two of three specific bands (24 kDa, 39 kDa, 41 kDa) must be present.
IgG: five or more of ten designated bands must be detected.

Results are reported as positive, negative, or indeterminate when the band pattern does not meet the threshold. Timing of testing is critical; specimens collected less than three weeks after exposure often lack detectable antibodies, leading to false‑negative outcomes.

Advantages of the Western blot include high specificity and the ability to differentiate between recent and past infection based on IgM versus IgG patterns. Limitations involve labor‑intensive procedures, longer turnaround time, and the requirement for skilled interpretation. When combined with a first‑tier enzyme immunoassay, the Western blot provides a robust confirmation strategy for diagnosing Lyme disease following a tick encounter.

Timing Considerations for Seroconversion

After a tick bite, clinicians typically request a two‑step serologic assay to detect antibodies against Borrelia burgdorferi, beginning with an enzyme immunoassay and confirming positive results with an immunoblot.

Seroconversion does not occur immediately. IgM antibodies usually become detectable 2–4 weeks after exposure; IgG antibodies generally appear 4–6 weeks post‑bite. Individual variation can shift these windows by several days.

Testing before the expected serologic window often yields false‑negative results. Practical timing guidelines are:

Perform the initial serology no earlier than 3 weeks after the bite or symptom onset.
If the first test is negative and clinical suspicion remains high, repeat the assay after an additional 2 weeks.
For patients presenting within the first week, consider direct detection methods (e.g., PCR of skin or blood) rather than serology.

Effective diagnosis relies on aligning specimen collection with the anticipated rise of antibodies, thereby maximizing the sensitivity of the two‑step serologic protocol.

Distinguishing Acute from Past Infection

Testing after a tick exposure aims to determine whether an infection is currently active or represents a resolved past exposure. The most widely used assay is a two‑step serologic protocol: an initial enzyme‑linked immunosorbent assay (ELISA) followed by a confirmatory immunoblot. The ELISA detects antibodies of two classes:

IgM appears within 1–3 weeks of infection, peaks around 4–6 weeks, and declines thereafter; its presence suggests a recent or ongoing infection.
IgG becomes detectable after 3–4 weeks, rises slowly, and can persist for months or years; a solitary IgG result without IgM indicates a prior, likely resolved infection.

When symptoms emerge within the first week after a bite, antibodies may be absent. In that window, polymerase chain reaction (PCR) testing of blood, skin biopsy, or cerebrospinal fluid can identify pathogen DNA, confirming an acute infection before seroconversion.

Interpretation guidelines:

Positive IgM + IgG – active infection, initiate treatment.
Positive IgM alone – early infection, consider repeat testing in 2 weeks to confirm seroconversion.
Positive IgG alone – past exposure, no current disease activity unless clinical signs suggest otherwise.
Negative serology with early symptoms – perform PCR; if PCR is negative, repeat serology after 2–3 weeks.

Accurate distinction between current and historical infection relies on timing of sample collection, the antibody class profile, and, when necessary, nucleic‑acid detection.

Molecular and Direct Detection Methods

Use of «Polymerase Chain Reaction» («PCR») Testing

Advantages of «PCR» for Early Detection

Polymerase‑chain reaction (PCR) is the preferred laboratory method for confirming exposure to tick‑borne pathogens shortly after a bite. By amplifying minute quantities of pathogen DNA, PCR delivers results when serologic tests remain negative because antibodies have not yet formed.

Key advantages for early detection include:

Sensitivity to low‑level infections, allowing identification of pathogens before clinical symptoms appear.
Rapid turnaround; most platforms produce a definitive result within 24 hours of specimen receipt.
Specificity for individual species, enabling targeted therapy and avoidance of broad‑spectrum antimicrobials.
Compatibility with various sample types (blood, skin biopsies, or tick remnants), increasing diagnostic flexibility.
Quantitative output that can monitor treatment efficacy and disease progression.

These attributes make PCR the most reliable assay for promptly diagnosing tick‑related illnesses, reducing the risk of severe complications through timely intervention.

Specimen Requirements for «PCR» Analysis

When a tick bite raises suspicion of a pathogen, polymerase chain reaction (PCR) is the preferred molecular assay for confirming infection. Proper specimen collection and handling are essential to preserve nucleic acid integrity and ensure reliable results.

The specimen must be:

Whole blood collected in an EDTA tube; anticoagulant prevents clotting that could degrade DNA.
Approximately 2–5 mL of blood, sufficient to extract the required amount of nucleic acid.
Processed within 24 hours of collection; if immediate processing is impossible, store at 4 °C for up to 12 hours, then freeze at –80 °C for longer periods.
Transported in a sealed, leak‑proof container, accompanied by a temperature log confirming cold‑chain maintenance.

For tissue or skin biopsies taken from the bite site:

Use a sterile scalpel to obtain a 3–5 mm fragment.
Place the tissue in a sterile, nucleic‑acid‑free tube with a minimal volume of RNA/DNA preservation solution (e.g., RNAlater) or transport medium.
Keep the specimen on ice and deliver to the laboratory within 12 hours; otherwise, freeze at –80 °C.

Additional considerations:

Label each sample with patient identifier, collection date, and specimen type.
Avoid hemolysis; gently invert tubes 5–10 times to mix anticoagulant.
Document any prior antimicrobial therapy, as it may affect pathogen load.

Adhering to these requirements maximizes the likelihood of detecting tick‑borne DNA, enabling accurate molecular diagnosis.

Alternative Diagnostic Approaches

Specialized Direct Antigen Tests

Specialized direct antigen tests detect pathogen components in specimens obtained after a tick bite, providing a rapid means to confirm infection without relying on antibody responses. These assays target surface proteins, flagellar proteins, or metabolic enzymes unique to the causative organism, most commonly Borrelia burgdorferi in Lyme disease.

Detection platforms include enzyme‑linked immunosorbent assays (ELISA), lateral flow immunochromatography, and chemiluminescent immunoassays. Each format captures antigens such as OspC, VlsE, or flagellin B, then generates a measurable signal proportional to antigen concentration.

Targets: outer‑surface protein C, VlsE, flagellin B, p41 (Borrelia)
Sample types: skin biopsies, whole blood, serum, cerebrospinal fluid
Turnaround time: 30 minutes to 2 hours, depending on platform
Sensitivity: highest during early disseminated phase when circulating antigen load peaks
Specificity: enhanced by using monoclonal antibodies against conserved epitopes

Clinical use focuses on early diagnosis when serologic conversion may be absent. Positive antigen results guide immediate antimicrobial therapy, while negative results in the acute window do not exclude infection and may be followed by repeat testing or complementary serology.

Laboratory Analysis of the Tick Specimen («Tick Testing»)

Laboratory analysis of a removed tick provides a direct method for identifying pathogens transmitted during the bite. The procedure, commonly referred to as tick testing, involves several validated techniques:

Polymerase chain reaction (PCR): Detects DNA of bacteria, viruses, or protozoa such as Borrelia burgdorferi, Anaplasma phagocytophilum, and Babesia microti.
Enzyme‑linked immunosorbent assay (ELISA): Screens for specific antigens or antibodies associated with tick‑borne infections.
Immunofluorescence assay (IFA): Visualizes pathogen presence using fluorescently labeled antibodies.
Culture methods: Rarely employed; isolate viable organisms for susceptibility testing when feasible.

Specimens are typically placed in sterile vials with ethanol or a suitable transport medium, then shipped to a certified reference laboratory within 24 hours. Laboratories follow strict chain‑of‑custody protocols to preserve sample integrity and ensure accurate results.

Interpretation of test outcomes must consider the tick species, geographic origin, and feeding duration. Positive detection of a pathogen does not guarantee clinical disease, but it guides clinicians in selecting appropriate prophylactic or therapeutic measures.

Patients should retain the tick for testing, label the container with collection date and location, and provide a brief exposure history to the laboratory. This systematic approach maximizes diagnostic yield and informs evidence‑based management of tick‑related illnesses.

Diagnostics for Co-Infections

Testing for Anaplasmosis and Ehrlichiosis

Testing for the bacterial infections transmitted by ticks, specifically Anaplasma phagocytophilum and Ehrlichia chaffeensis, relies on laboratory methods that detect the pathogen or the host’s immune response.

Molecular detection (polymerase chain reaction) identifies pathogen DNA in whole blood and provides the most rapid confirmation, particularly during the acute phase when bacterial load is highest. Real‑time PCR assays target species‑specific genes such as msp2 for Ehrlichia and 16S rRNA for Anaplasma, delivering results within 24 hours.

Serologic testing assesses antibodies against the organisms. Indirect immunofluorescence assay (IFA) remains the reference method; a single serum sample with a high titer suggests recent infection, while a four‑fold rise between acute and convalescent samples confirms diagnosis. Enzyme‑linked immunosorbent assay (ELISA) offers a high‑throughput alternative with comparable sensitivity.

Microscopic examination of a peripheral blood smear can reveal morulae within neutrophils (Ehrlichia) or granulocytes (Anaplasma). This approach is inexpensive but less sensitive, useful when laboratory resources are limited.

Typical diagnostic workflow:

Collect whole blood in EDTA tube for PCR and smear.
Draw serum for IFA or ELISA; obtain a second sample 2–4 weeks later if initial titer is low.
Perform PCR first if symptoms began within 1–2 weeks of tick exposure.
Use serology to support diagnosis when PCR is negative or when presentation is delayed.

Interpretation considers the timing of specimen collection, clinical picture, and geographic prevalence of tick‑borne pathogens. Positive PCR during early illness confirms infection; seroconversion or a significant rise in antibody titer validates exposure in later stages.

Identification of Babesiosis Parasites

Examination of Peripheral Blood Smears

Examination of peripheral blood smears provides a rapid microscopic assessment of organisms that may be transmitted by ticks. A thin film of anticoagulated blood is spread on a glass slide, fixed, and stained with Giemsa or Wright reagents. Under oil immersion, the observer evaluates erythrocytes, leukocytes, and platelets for characteristic intracellular or extracellular forms.

Typical microscopic findings associated with tick exposure include:

Babesia spp.: ring‑shaped parasites, sometimes forming the distinctive “Maltese cross” within red cells.
Ehrlichia spp.: basophilic intracytoplasmic inclusions (morulae) in neutrophils or monocytes.
Anaplasma phagocytophilum: similar morulae, primarily in neutrophils.
Rickettsial organisms: rarely visible, but endothelial cell changes may be noted.

The test offers immediate visual confirmation, requires minimal laboratory infrastructure, and can be performed on fresh or stored specimens. Limitations comprise reduced sensitivity when parasitemia is low, operator‑dependent interpretation, and inability to identify species without supplemental molecular methods. For definitive diagnosis, peripheral smear results are often combined with polymerase chain reaction or serologic assays.

Management of Multiple Pathogens

The diagnostic approach for a suspected tick exposure relies on a multiplex polymerase chain reaction (PCR) panel that simultaneously detects DNA from the most common tick‑borne organisms. This assay, often referred to as a tick‑borne disease panel, provides rapid identification of pathogens such as Borrelia burgdorferi, Anaplasma phagocytophilum, Ehrlichia chaffeensis, Rickettsia spp., and Babesia spp.

Effective management of the multiple pathogens identified by the panel includes:

Immediate initiation of pathogen‑specific antimicrobial therapy (e.g., doxycycline for bacterial agents, atovaquone‑azithromycin for Babesia).
Assessment of disease severity and organ involvement to determine need for hospitalization.
Monitoring of laboratory markers (complete blood count, liver enzymes, renal function) to track treatment response.
Follow‑up serologic testing when indicated to confirm clearance or identify late seroconversion.
Patient education on preventive measures (protective clothing, repellents, prompt tick removal) to reduce reinfection risk.

Co‑infection is common; therefore, treatment regimens must cover all detected agents without delay. Adjustments to therapy are guided by antimicrobial susceptibility data, patient allergies, and comorbid conditions. Continuous surveillance of regional tick‑borne pathogen prevalence informs selection of the most appropriate diagnostic panel and empirical treatment protocols.

Interpretation and Clinical Implications

Factors Influencing Test Accuracy

Diagnosing tick‑borne infections depends on laboratory assays whose reliability varies with several controllable and inherent factors.

Timing of specimen collection – Early samples may lack detectable antibodies or pathogen DNA, while later samples improve sensitivity but risk false‑positive serology due to lingering antibodies.
Assay type – Enzyme‑linked immunosorbent assays (ELISA), immunoblot, polymerase chain reaction (PCR), and culture each have distinct limits of detection; PCR excels for acute infection, whereas serology is more informative for past exposure.
Specimen quality – Proper handling, storage temperature, and avoidance of contamination preserve nucleic acids and proteins essential for accurate measurement.
Prior antimicrobial therapy – Antibiotics administered before sampling can suppress pathogen load, reducing PCR positivity and attenuating antibody responses.
Cross‑reactivity – Antibodies generated against related organisms may bind assay targets, inflating false‑positive rates, especially in regions with high prevalence of other spirochetes.
Laboratory expertise – Technician proficiency, calibration of equipment, and adherence to validated protocols directly affect reproducibility and error rates.
Epidemiological prevalence – In low‑incidence areas, the positive predictive value of any test declines, making confirmatory testing essential.

Understanding and managing these variables enhances the diagnostic precision of the test employed after a tick bite, supporting timely clinical decisions.

Guidelines for Test Result Management

Managing the outcomes of the diagnostic assay used after a tick exposure requires a systematic approach to ensure accuracy, timely communication, and appropriate clinical action.

The laboratory should first verify patient identification and sample integrity before processing. Once the assay—commonly a two‑tier serologic test for Borrelia infection—has been completed, the result must be entered into a secure information system with a timestamp and the analyst’s signature.

Interpretation guidelines:

Positive screening (ELISA) followed by confirmatory immunoblot indicates active infection; document the specific IgM and IgG bands.
Negative screening excludes current infection; record the assay’s sensitivity range.
Equivocal results demand repeat testing or alternative methods; note the rationale for retesting.

Communication protocol:

Deliver final reports to the ordering clinician through encrypted electronic health records within 24 hours of verification.
Include a concise interpretation, recommended next steps, and reference ranges.
Notify the clinician immediately for results that necessitate urgent treatment, such as a positive confirmatory test.

Documentation requirements:

Archive raw data, quality control logs, and interpretive comments for a minimum of seven years.
Maintain a log of result disclosures, including date, recipient, and method of transmission.

Follow‑up actions:

Encourage clinicians to schedule patient counseling within 48 hours of a positive result.
Recommend repeat serology at 4–6 weeks for cases with initial equivocal findings.
Record any subsequent testing and clinical outcomes to facilitate audit and quality improvement.

Treatment Protocols Following Positive Diagnosis

A confirmed tick‑borne infection requires immediate antimicrobial therapy to prevent tissue damage and systemic complications. The choice of drug, dosage, and treatment length depends on the identified pathogen, disease stage, patient age, and pregnancy status.

Early localized infection (≤ 72 hours of rash)
Doxycycline 100 mg orally twice daily for 10–14 days (children < 8 years: amoxicillin 500 mg three times daily).
Early disseminated disease (multiple skin lesions, neurologic signs, cardiac involvement)
Doxycycline 100 mg twice daily for 21 days; if cardiac involvement is present, consider intravenous ceftriaxone 2 g daily for 14–21 days.
Late disseminated disease (arthritis, chronic neurologic manifestations)
Doxycycline 100 mg twice daily for 28 days or oral cefuroxime axetil 500 mg twice daily for 28 days; intravenous ceftriaxone 2 g daily for 28 days may be required for severe neurologic disease.
Pregnant or breastfeeding patients
Amoxicillin 500 mg three times daily for 14–21 days; cefuroxime 500 mg twice daily is an alternative.
Pediatric patients (< 12 years)
Amoxicillin 50 mg/kg/day divided every 8 hours for 14–21 days; cefuroxime 30 mg/kg/day divided every 12 hours is acceptable.

Supportive measures include anti‑inflammatory agents for arthritis, cardiac monitoring for conduction abnormalities, and education on tick‑bite prevention. Follow‑up serology is recommended 4–6 weeks after treatment completion to confirm serologic decline; persistent antibodies do not necessarily indicate treatment failure. If symptoms recur or persist beyond the expected resolution period, reassessment with repeat testing and possible extension of antimicrobial therapy is warranted.