Where should blood be taken for tick‑borne infections? - briefly
Blood for diagnosing tick‑borne diseases is usually obtained by venipuncture of a peripheral vein, most commonly the antecubital fossa. A capillary finger‑stick sample can be used for rapid point‑of‑care tests, but most laboratories require a venous specimen for definitive analysis.
Where should blood be taken for tick‑borne infections? - in detail
Blood sampling for tick‑borne diseases should be performed by venipuncture from a peripheral vein, most commonly the median cubital vein. This site provides sufficient volume for multiple assays and minimizes hemolysis risk.
For pathogens detected by polymerase chain reaction—such as Babesia, Anaplasma, Ehrlichia, and early‑stage Rickettsia—collect 3–5 mL of whole blood into an EDTA tube. EDTA preserves nucleic acids and prevents clotting, allowing accurate PCR amplification.
Serologic testing, required for later stages of Lyme disease, Rocky Mountain spotted fever, and Powassan virus, uses serum. After drawing an additional 5–10 mL of blood into a serum‑separator tube, allow clotting for 30 minutes, then centrifuge and store the serum at –20 °C or colder until testing.
When both molecular and antibody assays are needed, split the sample:
- EDTA tube: whole blood for PCR, stored at –80 °C if delay exceeds 24 hours.
- Serum tube: for ELISA, immunofluorescence assay, or Western blot, stored at –20 °C.
Timing of collection influences diagnostic yield:
- Acute phase (days 1–7): prioritize whole‑blood PCR to capture circulating pathogens before antibody production.
- Convalescent phase (days 14–28): obtain serum for paired serology, comparing acute and follow‑up titers.
Special populations require adjustments. In infants and small children, use a 22‑gauge butterfly needle to obtain 2–3 mL of venous blood, allocating the same proportion to EDTA and serum tubes. Capillary finger‑stick samples are insufficient for PCR and should be avoided except when venous access is impossible and only rapid antigen testing is performed.
Do not collect blood from sites with active infection or inflammation, such as the area surrounding a recent tick bite, to prevent localized immune interference.
In summary, optimal sampling for tick‑borne infections involves peripheral venous puncture, allocation of blood into EDTA and serum tubes, and timing that matches the pathogen’s diagnostic window. This approach maximizes the sensitivity of both molecular and serologic assays, ensuring reliable detection across the spectrum of tick‑transmitted diseases.