What will a blood test show after a tick bite? - briefly
A blood analysis can identify antibodies or genetic material of tick‑borne organisms (e.g., Borrelia, Anaplasma, Babesia), confirming recent infection. It may also show increased inflammatory markers if the bite has provoked a systemic response.
What will a blood test show after a tick bite? - in detail
A blood analysis performed after a tick attachment is used to detect infection, assess immune response, and rule out complications. The most common pathogens transmitted by ticks in temperate regions are Borrelia burgdorferi (Lyme disease), Anaplasma phagocytophilum (anaplasmosis), Babesia microti (babesiosis), and Rickettsia species (spotted fever). Specific laboratory findings for each agent are listed below.
- Lyme disease – Enzyme‑linked immunosorbent assay (ELISA) for IgM and IgG antibodies against B. burgdorferi followed by Western blot confirmation. Early infection may show a positive IgM with a rising titer; later stages display IgG seroconversion. Polymerase chain reaction (PCR) on blood is less sensitive but can be employed when serology is equivocal.
- Anaplasmosis – Indirect immunofluorescence assay (IFA) detecting IgG antibodies; a four‑fold rise between acute and convalescent samples confirms infection. PCR targeting the 16S rRNA gene provides rapid detection during the acute phase, often before antibodies develop.
- Babesiosis – Thick‑smear microscopy reveals intra‑erythrocytic parasites; quantitative PCR measures parasitemia. Serologic testing (IFA) for IgG may indicate past exposure but does not differentiate active disease.
- Rickettsial infections – IFA for specific IgM/IgG antibodies; a significant increase in titer between paired sera confirms diagnosis. PCR on whole blood or tissue samples can identify Rickettsia DNA early in the illness.
Additional laboratory parameters can signal systemic effects of tick‑borne diseases:
- Complete blood count (CBC) – Anaplasmosis frequently causes leukopenia and thrombocytopenia; babesiosis may produce anemia and elevated lactate dehydrogenase (LDH); Lyme disease can lead to mild lymphocytosis.
- Liver function tests (ALT, AST, alkaline phosphatase) – Mild elevations are common in anaplasmosis and babesiosis, reflecting hepatic involvement.
- Inflammatory markers – C‑reactive protein (CRP) and erythrocyte sedimentation rate (ESR) often rise in acute infection but lack specificity.
When a tick bite occurs in an area where emerging pathogens such as Powassan virus or Ehrlichia spp. are present, clinicians may order PCR panels that screen for multiple agents simultaneously. Negative results across all assays reduce the likelihood of a tick‑borne infection but do not eliminate the need for clinical monitoring, especially if the bite was recent and symptoms have not yet manifested.
In summary, a post‑exposure blood workup can reveal:
- Serologic conversion indicating exposure to specific spirochetes, rickettsiae, or protozoa.
- Direct detection of pathogen DNA/RNA via PCR during the early phase.
- Hematologic and biochemical changes reflecting organ involvement.
- Evidence of co‑infection when multiple agents are identified in the same sample.
These findings guide targeted antimicrobial therapy and inform prognosis.