What is the name of the blood test after a tick bite?

Understanding Tick-Borne Diseases

The Importance of Prompt Testing

A blood assay is recommended after a tick bite to identify infection with Borrelia burgdorferi. The test typically begins with an enzyme‑linked immunosorbent assay (ELISA) and, if positive, proceeds to a Western blot for confirmation.

Prompt testing yields several clinical advantages:

Detects seroconversion before symptoms appear, allowing immediate antibiotic therapy.
Limits the risk of disseminated disease, which can involve joints, heart, and nervous system.
Reduces the duration of treatment needed, decreasing exposure to medication side effects.
Provides objective data for patient counseling and public‑health reporting.

Guidelines from the Infectious Diseases Society of America advise sampling within 2–4 weeks of a confirmed tick bite when exposure is known or when early skin lesions are present. Delaying beyond this window diminishes assay sensitivity because antibody levels may not have risen sufficiently, leading to false‑negative results.

Early identification also facilitates monitoring of treatment response. Baseline serology establishes a reference point; follow‑up samples can verify clearance of infection or detect persistent antibody titers that may indicate relapse.

In summary, conducting the appropriate blood test promptly after a tick bite maximizes diagnostic accuracy, shortens disease course, and improves long‑term health outcomes.

Common Tick-Borne Pathogens

After a tick attachment, clinicians typically request a diagnostic assay known as a tick‑borne disease panel. The panel combines serologic methods such as enzyme‑linked immunosorbent assay (ELISA) and immunoblot for Borrelia, and nucleic‑acid amplification tests (PCR) for bacterial and protozoal agents. The result identifies exposure to the most prevalent pathogens transmitted by ixodid ticks.

Common tick‑borne pathogens evaluated by this panel include:

Borrelia burgdorferi – agent of Lyme disease
Anaplasma phagocytophilum – causes anaplasmosis
Ehrlichia chaffeensis – responsible for ehrlichiosis
Babesia microti – triggers babesiosis
Rickettsia rickettsii – produces Rocky Mountain spotted fever
Powassan virus – leads to encephalitis

The panel’s comprehensive approach enables early detection and targeted therapy for infections acquired through tick bites.

Diagnostic Approaches for Tick Bites

Direct Pathogen Detection Tests

Polymerase Chain Reaction («PCR») Testing

A molecular blood assay is commonly ordered after a tick bite to identify infectious agents.

Polymerase Chain Reaction (PCR) testing amplifies targeted DNA sequences, allowing detection of minute quantities of pathogen genetic material in a serum or whole‑blood sample.

Typical targets include:

Borrelia burgdorferi (Lyme disease)
Anaplasma phagocytophilum (anaplasmosis)
Babesia microti (babesiosis)
Rickettsia spp. (spotted fever group)

Key practical points:

Blood is drawn into anticoagulant tubes; plasma or whole blood may be used.
Optimal sensitivity occurs when the sample is collected 1–3 weeks after the bite, coinciding with peak pathogenemia.
PCR provides high specificity; false‑positive results are rare when proper controls are employed.
Negative PCR does not exclude infection if sampling occurs too early or after antimicrobial therapy.

PCR testing thus serves as the definitive laboratory method for confirming tick‑borne infections when serologic assays are inconclusive or when rapid diagnosis is required.

Antigen Detection Tests

Antigen detection assays are the primary laboratory method employed to confirm infection following a tick bite. The test identifies specific proteins of Borrelia burgdorferi, the bacterium that causes Lyme disease, directly in patient serum or plasma. Commercial kits are marketed under names such as Lyme ELISA, Lyme Immunoblot, and rapid antigen‑capture assays.

Key characteristics of these assays include:

Use of monoclonal or polyclonal antibodies to bind Borrelia antigens.
Quantitative or qualitative readout, often expressed as optical density or signal intensity.
Sensitivity that increases after the first two weeks of infection, when bacterial load in blood peaks.
Specificity enhanced by incorporating recombinant antigens (e.g., VlsE, OspC) that reduce cross‑reactivity with other spirochetes.

Interpretation follows a two‑tiered protocol: a positive antigen detection result triggers a confirmatory Western blot or immunoblot to verify the presence of multiple Borrelia proteins. Negative results obtained within the early window period do not exclude infection; repeat testing after 2–3 weeks is recommended.

Antibody Detection Tests

Enzyme-Linked Immunosorbent Assay («ELISA»)

Enzyme‑Linked Immunosorbent Assay (ELISA) is the standard serologic method employed to evaluate patients after a tick bite when Lyme disease is suspected. The assay detects IgM and IgG antibodies directed against Borrelia burgdorferi antigens, providing quantitative results that guide clinical decisions.

Key characteristics of ELISA in this context:

Target antibodies: IgM (early infection) and IgG (later stages).
Specimen: Venous whole blood or serum collected 2–4 weeks post‑exposure, when antibody levels become measurable.
Sensitivity: Approximately 85 %–95 % for confirmed cases, increasing with disease progression.
Specificity: Ranges from 90 % to 98 %, with false‑positive risk reduced by using recombinant antigens.
Interpretation: Positive results require confirmatory testing (e.g., Western blot) to differentiate true infection from cross‑reactivity.
Turnaround: Results typically available within 24 hours, facilitating prompt treatment decisions.

The ELISA workflow includes coating microtiter plates with B. burgdorferi antigens, adding patient serum, washing away unbound components, introducing enzyme‑linked secondary antibodies, and measuring colorimetric change proportional to antibody concentration. This quantitative output enables clinicians to assess exposure, monitor seroconversion, and evaluate therapeutic response after a tick bite.

Western Blot Test

The blood test commonly ordered after a tick bite to confirm Lyme disease is the Western Blot assay. This method detects antibodies that the immune system produces in response to infection with Borrelia burgdorferi.

During the test, patient serum is mixed with proteins extracted from the bacterium. The proteins are separated by electrophoresis, transferred onto a membrane, and incubated with the serum. If specific antibodies are present, they bind to the corresponding protein bands, which become visible after adding a labeled secondary antibody.

Interpretation follows established criteria:

Presence of at least two of the three diagnostic bands for IgM (24 kDa, 39 kDa, 41 kDa) indicates a recent infection.
Presence of at least five of the ten diagnostic bands for IgG (including 18 kDa, 23 kDa, 28 kDa, 30 kDa, 39 kDa, 41 kDa, 45 kDa, 58 kDa, 66 kDa, 93 kDa) suggests a later-stage or persistent infection.

The assay is performed after an initial enzyme‑linked immunosorbent assay (ELISA) yields a positive or equivocal result. Western Blot provides higher specificity, reducing false‑positive diagnoses that can occur with ELISA alone.

Limitations include reduced sensitivity in the early days post‑exposure, when antibody levels may be undetectable, and potential cross‑reactivity with antibodies from other spirochetal infections. Clinicians must consider timing of the test, clinical presentation, and epidemiological exposure when interpreting results.

Complete Blood Count («CBC») and Other Non-Specific Tests

A complete blood count (CBC) is frequently ordered when a patient presents after a tick bite. The CBC provides quantitative data on red and white blood cells, hemoglobin, hematocrit, and platelets, allowing clinicians to detect anemia, leukocytosis, leukopenia, or thrombocytopenia that may signal early infection or immune response.

In addition to the CBC, physicians often request non‑specific laboratory studies that support a broader assessment:

Erythrocyte sedimentation rate (ESR) or C‑reactive protein (CRP) to gauge systemic inflammation.
Liver function panel (ALT, AST, bilirubin) to identify hepatic involvement.
Renal function tests (creatinine, BUN) to monitor kidney status.
Serum electrolytes and glucose to evaluate metabolic balance.

These tests do not diagnose a specific tick‑borne disease but help identify abnormalities that prompt further targeted investigations, such as serology or polymerase chain reaction assays for Lyme disease, anaplasmosis, or babesiosis. The combined results guide clinical decision‑making and treatment planning.

Specific Tests for Lyme Disease

Two-Tiered Testing Protocol

Initial Screening: ELISA

The blood test most commonly ordered after a tick bite is an enzyme‑linked immunosorbent assay (ELISA) used as the initial screening for Lyme disease. ELISA detects antibodies—IgM and IgG—produced in response to Borrelia burgdorferi. The assay employs recombinant antigens to increase specificity and reduces cross‑reactivity with other spirochetes.

Key points for clinicians:

Timing: Blood should be drawn at least 2–3 weeks after the bite or onset of symptoms; earlier sampling may yield false‑negative results because antibodies have not yet reached detectable levels.
Interpretation:
1. Negative result – suggests absence of exposure; no further testing required unless clinical suspicion remains high.
2. Positive or equivocal result – requires confirmation with a Western blot (IgM/IgG) to differentiate true infection from nonspecific reactivity.
Sensitivity and specificity: ELISA sensitivity ranges from 70 % to 90 % in early disseminated disease, while specificity exceeds 95 % when recombinant antigens are used.
Sample handling: Serum or plasma collected in clot‑activator tubes; avoid hemolysis, which can interfere with optical density readings.

The ELISA serves as the first step in a two‑tier diagnostic algorithm, providing a rapid, cost‑effective screen before more labor‑intensive confirmatory testing.

Confirmatory Test: Western Blot

The definitive laboratory assay used to verify infection after a tick bite is the Western blot.

The Western blot follows an initial screening test—typically an enzyme‑linked immunosorbent assay (ELISA)—and provides confirmation by detecting antibodies that bind to specific protein bands of the pathogen. Each band corresponds to a distinct antigen; the pattern of reactive bands determines a positive or negative result according to established criteria.

Key characteristics of the Western blot:

Targets IgM and IgG antibodies against defined protein fragments.
Requires a serum sample collected at least 2–4 weeks after exposure for optimal sensitivity.
Interpreted by comparing the observed band profile to reference standards; a certain number of bands must be present for a confirmed diagnosis.
Offers high specificity, reducing false‑positive rates inherent to screening assays.

Clinical relevance: a positive Western blot confirms the presence of antibodies to the tick‑borne organism, guiding treatment decisions and public‑health reporting. A negative result, despite a positive screening test, suggests either early infection before seroconversion or a false‑positive screening outcome, prompting repeat testing after an appropriate interval.

Challenges in Lyme Disease Diagnosis

The blood assay most commonly ordered after a tick bite is a two‑step serologic evaluation for Borrelia burgdorferi, beginning with an enzyme‑linked immunosorbent assay (ELISA) followed by a confirmatory Western blot or a C6 peptide ELISA.

Diagnosing Lyme disease with this approach encounters several obstacles:

Seroconversion delay: Antibody production may not be detectable until 2–4 weeks post‑exposure, producing false‑negative results in early infection.
Variable test sensitivity: ELISA sensitivity ranges from 50 % to 70 % in early disease, improving to >90 % in later stages; clinicians must interpret negative results cautiously.
Cross‑reactivity: Antibodies against other spirochetes or common infections (e.g., syphilis, Epstein‑Barr virus) can generate false‑positive ELISA outcomes, necessitating confirmatory testing.
Lack of standardization: Different laboratories use distinct antigen preparations and cutoff values, leading to inconsistent results across providers.
Interpretation complexity: Western blot criteria differ between U.S. and European guidelines, and borderline bands may be reported ambiguously.
PCR limitations: Molecular detection of Borrelia DNA in blood is rarely positive due to low bacteremia, restricting its utility to specific tissue samples.

Effective management requires combining laboratory data with detailed exposure history, clinical signs, and, when appropriate, repeat testing after the seroconversion window.

Tests for Other Tick-Borne Illnesses

Anaplasmosis and Ehrlichiosis

Indirect Fluorescent Antibody («IFA») Test

The Indirect Fluorescent Antibody (IFA) test is the standard serologic assay used to detect antibodies against tick‑borne pathogens such as Borrelia burgdorferi (Lyme disease), Anaplasma phagocytophilum, and Rickettsia species. Blood is drawn 2–4 weeks after exposure; the serum is incubated with antigen‑coated slides, followed by a fluorescein‑labeled anti‑human IgG antibody. Under a fluorescence microscope, specific binding appears as bright spots, confirming the presence of pathogen‑specific antibodies.

Key characteristics of the IFA test:

Sensitivity ≈ 85–95 % for established infections; lower during early seroconversion.
Specificity ≈ 90 % when validated antigen panels are employed.
Turnaround time ≈ 1–2 days after specimen receipt.
Interpretation requires comparison with a paired acute‑ and convalescent‑phase sample; a four‑fold rise in titer indicates recent infection.

Advantages include high specificity for a broad range of tick‑borne agents and the ability to differentiate between closely related species. Limitations involve reduced sensitivity during the first week after bite, reliance on experienced microscopy, and potential cross‑reactivity with other spirochetal infections.

Clinical use:

Ordered when a patient presents with erythema migrans, fever, or neurologic symptoms following a tick bite.
Guides antimicrobial therapy by confirming the causative organism.
Provides epidemiologic data for public‑health surveillance of tick‑borne diseases.

PCR Testing

Polymerase chain reaction (PCR) is the standard blood assay employed after a tick bite to identify pathogen DNA. The method amplifies minute quantities of genetic material, allowing detection of infections before serologic antibodies become measurable.

A clinician orders the test when a patient reports recent exposure to ticks and exhibits early symptoms such as fever, rash, or joint pain. Blood is drawn into an anticoagulant tube; the specimen is processed within 24 hours to preserve nucleic acids. Results are typically available within 48–72 hours.

PCR can target several tick‑borne organisms, including:

Borrelia burgdorferi (Lyme disease)
Anaplasma phagocytophilum (anaplasmosis)
Ehrlichia chaffeensis (ehrlichiosis)
Babesia microti (babesiosis)
Rickettsia species (spotted fever group)

Positive amplification confirms active infection, guiding immediate antimicrobial therapy. Negative PCR does not exclude later seroconversion; follow‑up testing may be required if symptoms persist.

Rocky Mountain Spotted Fever

Serologic Tests

Serologic testing is the standard laboratory method used to evaluate a patient after a tick bite when infection with Borrelia burgdorferi is suspected. The assay detects antibodies generated in response to the spirochete and guides clinical decision‑making.

The typical serologic algorithm consists of two steps:

Enzyme‑linked immunosorbent assay (ELISA) – screens for IgM and IgG antibodies; a positive result triggers confirmatory testing.
Western blot – separates B. burgdorferi proteins by electrophoresis and identifies antibody binding to specific antigenic bands; distinguishes early (IgM) from later (IgG) immune responses.

Interpretation depends on the interval between exposure and specimen collection. IgM antibodies may appear 2–4 weeks after the bite, while IgG antibodies usually become detectable after 4–6 weeks. A negative result obtained too early does not exclude infection; repeat testing after an appropriate interval is recommended.

Limitations include cross‑reactivity with other infections, false‑positive results in endemic areas, and reduced sensitivity in early localized disease before seroconversion. Consequently, serologic results must be correlated with clinical findings such as erythema migrans, neurological symptoms, or arthritic manifestations.

In practice, the combination of ELISA screening followed by Western blot confirmation provides the most reliable serologic assessment after a tick bite, enabling timely initiation of antimicrobial therapy when indicated.

Babesiosis

Blood Smear Examination

Blood smear examination is a diagnostic procedure frequently ordered after a patient reports a recent tick exposure. The test involves spreading a thin layer of peripheral blood on a glass slide, fixing the cells, and staining them with Roman‑Romanowsky dyes such as Giemsa or Wright. Under a light microscope, laboratory professionals evaluate the morphology of red and white blood cells and search for intracellular organisms.

Key objectives of the smear in the setting of a tick bite include:

Detection of Babesia parasites within erythrocytes, which appear as ring forms or Maltese‑cross tetrads.
Identification of Ehrlichia or Anaplasma morulae inside neutrophils or monocytes.
Assessment of platelet count and morphology, which may be altered in tick‑borne infections.

The procedure provides rapid visual evidence, typically within a few hours of specimen receipt. Sensitivity varies with the pathogen load; early infection or low parasitemia can yield false‑negative results. Consequently, clinicians often combine smear findings with serologic assays (e.g., indirect immunofluorescence) or molecular tests (PCR) to confirm the diagnosis.

Interpretation requires expertise in distinguishing true pathogenic inclusions from artifacts. Experienced technologists apply standardized criteria to report presence, quantity, and species‑specific features. Results guide therapeutic decisions, such as initiating doxycycline for ehrlichiosis or atovaquone‑azithromycin for babesiosis.

In summary, blood smear examination offers a direct, time‑efficient method to visualize tick‑transmitted organisms and evaluate hematologic alterations, serving as an essential component of the diagnostic work‑up after a tick bite.

PCR Testing

PCR testing is the primary laboratory method used to detect pathogen DNA in a blood sample after a tick exposure. The assay amplifies short segments of genetic material, allowing identification of organisms such as Borrelia burgdorferi (the cause of Lyme disease) within hours of collection.

Key characteristics of PCR testing for tick‑borne infections:

Specimen type: Whole blood, serum, or plasma collected in an anticoagulant tube.
Timing: Optimal sensitivity between 2 weeks and 1 month post‑bite; earlier samples may yield false‑negative results.
Target genes: Species‑specific sequences (e.g., flaB, ospA for Borrelia), providing high specificity.
Result turnaround: Typically 24–48 hours from receipt in the laboratory.

Clinical utility derives from its ability to confirm infection when serology is inconclusive, to differentiate between co‑infecting agents (e.g., Anaplasma, Ehrlichia), and to guide antimicrobial therapy promptly.

Factors Influencing Test Selection

Timing of the Tick Bite

The interval between a tick attachment and the collection of a blood sample determines the reliability of serologic detection. A bite that occurred within the past 24 hours is unlikely to produce detectable antibodies; the immune response generally requires at least 5–7 days to become measurable. Testing performed before this window yields a high probability of false‑negative results.

Guidelines for optimal timing:

0–4 days after bite: No serologic testing recommended; focus on prompt tick removal and observation for erythema migrans.
5–14 days: First‑line enzyme‑linked immunosorbent assay (ELISA) may detect early IgM antibodies; a positive result should be confirmed with a Western blot.
15–30 days: IgG antibodies become detectable; repeat ELISA and confirmatory Western blot improve diagnostic accuracy.
Beyond 30 days: Persistent or late‑stage infection may be assessed with the same assays; PCR on blood or tissue specimens can supplement serology when neurological or cardiac involvement is suspected.

Accurate documentation of the bite date enables clinicians to select the appropriate testing window, reducing misdiagnosis and guiding timely treatment.

Symptoms and Clinical Presentation

A tick bite can introduce Borrelia burgdorferi, the spirochete responsible for Lyme disease. Early manifestations typically appear within three to thirty days and include a circular erythema migrans lesion that expands outward, often exceeding five centimeters in diameter. The rash may be warm, but it is usually painless. Accompanying systemic signs consist of fever, chills, headache, fatigue, and myalgias. In some cases, patients report neck stiffness or facial nerve palsy, indicating early neuroborreliosis.

If the infection progresses, later stages present with arthritis, most frequently affecting large joints such as the knee. Joint swelling is often intermittent and may be accompanied by erythema and limited range of motion. Neurologic involvement can evolve into peripheral neuropathy, radiculopathy, or encephalopathy, producing sensory disturbances, tremor, or cognitive deficits. Cardiac involvement, though less common, manifests as atrioventricular conduction abnormalities, detectable by electrocardiography.

The laboratory evaluation appropriate after a tick exposure is a two‑tier serologic protocol. The initial screening employs an enzyme‑linked immunosorbent assay (ELISA) to detect IgM and IgG antibodies against B. burgdorferi. A positive ELISA is confirmed by a Western blot, which identifies specific protein bands characteristic of the pathogen. Positive serology, in conjunction with the clinical picture described above, confirms the diagnosis and guides antimicrobial therapy.

Geographic Location and Endemic Diseases

Geographic distribution determines which tick‑borne pathogens are likely to be encountered, and therefore which serologic assay should be ordered after a bite. In regions where Borrelia burgdorferi predominates, a two‑tier Lyme disease test—first an enzyme immunoassay (EIA) or immunofluorescence assay (IFA), followed by a Western blot if positive—is standard. In the southeastern United States, where Ehrlichia chaffeensis and Anaplasma phagocytophilum are endemic, a polymerase chain reaction (PCR) panel or indirect immunofluorescence assay for ehrlichiosis and anaplasmosis is recommended. In parts of Europe and Asia where tick‑borne encephalitis virus circulates, a specific IgM/IgG ELISA for TBEV is indicated. When multiple pathogens co‑occur, a multiplex PCR or broad‑spectrum serology panel may be employed.

Typical endemic agents and their preferred diagnostic tests:

Borrelia burgdorferi – EIA/IFA screening, confirmatory Western blot
Ehrlichia spp. – PCR or indirect immunofluorescence assay
Anaplasma spp. – PCR or indirect immunofluorescence assay
Tick‑borne encephalitis virus – IgM/IgG ELISA
Rickettsia spp. – Immunofluorescence assay or PCR

Selection of the appropriate blood test depends on the patient’s travel history, local tick species, and known disease prevalence in the area of exposure.

Interpretation of Test Results

Understanding False Positives and False Negatives

The blood assay used after a tick attachment is typically an enzyme‑linked immunosorbent assay (ELISA) followed by a confirmatory Western blot. Both steps are vulnerable to inaccurate results, which can misguide clinical decisions.

False‑positive contributors

Cross‑reactive antibodies from other infections (e.g., Epstein‑Barr virus, syphilis)
Recent vaccination or exposure to unrelated bacterial antigens
Laboratory contamination or improper sample handling
Low‑specificity ELISA kits lacking stringent cutoff values

False‑negative contributors

Testing performed before antibody levels rise (seroconversion window)
Immunosuppression reducing antibody production
Early infection with low bacterial load, below assay detection limits
Use of outdated or poorly validated reagents

Interpretation requires correlating laboratory data with clinical presentation and exposure history. Repeating the test after an appropriate interval or employing alternative methods such as polymerase chain reaction (PCR) can resolve ambiguous outcomes.

The Role of Medical Professionals in Diagnosis

Medical practitioners must assess a patient’s exposure to ticks, document any rash or systemic symptoms, and decide whether laboratory evaluation is warranted. The standard blood assay ordered after a tick bite is a Lyme disease serologic panel, typically beginning with an enzyme‑linked immunosorbent assay (ELISA) and, if positive, followed by a Western blot for confirmation. Clinicians determine the appropriate timing of specimen collection, usually 2‑4 weeks post‑exposure, to maximize antibody detection and reduce false‑negative results.

Key responsibilities of health‑care providers include:

Collecting a detailed exposure and symptom history.
Selecting the serologic test based on clinical presentation and epidemiologic risk.
Interpreting ELISA and Western blot results in the context of disease stage.
Communicating findings to the patient and outlining treatment options when infection is confirmed.
Arranging follow‑up testing for equivocal or early‑stage cases.

Effective diagnosis relies on the practitioner’s ability to integrate clinical judgment with laboratory data, ensuring timely and accurate identification of tick‑borne infection.

Follow-up Testing and Monitoring

After a tick attachment, clinicians typically schedule a serologic evaluation to detect Borrelia infection. The standard assay is an enzyme‑linked immunosorbent test (ELISA) performed on a blood sample, often followed by a confirmatory immunoblot if the initial result is positive. This two‑step approach constitutes the primary diagnostic protocol for Lyme disease.

Follow‑up testing is recommended at specific intervals to capture seroconversion that may occur after the initial exposure. Common schedules include:

Baseline blood draw at the time of presentation or within a few days of the bite.
Repeat serology 2–4 weeks later to identify emerging antibodies.
Additional testing at 6–8 weeks if symptoms persist or if the earlier results were equivocal.

Monitoring extends beyond laboratory values. Patients should be instructed to report new or worsening signs such as erythema migrans, fever, fatigue, joint pain, or neurologic changes. Documentation of symptom progression guides decisions about repeat testing or initiation of antimicrobial therapy.

Interpretation of results must consider the timing of the bite, the stage of infection, and the possibility of false‑negative early ELISA outcomes. A negative baseline test does not exclude later seroconversion; therefore, clinicians rely on the scheduled repeat assays and clinical observation to ensure timely detection and treatment.