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Capillary and Dermal Puncture Flashcards

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  1. When performing a fingerstick on an adult patient, which finger is the PREFERRED site?

    Answer: Middle or ring finger

    The middle (third) and ring (fourth) fingers are preferred for adult fingersticks because they have adequate tissue depth and fewer nerve endings than the index finger.

  2. Why is the first drop of blood wiped away during a capillary puncture?

    Answer: To remove tissue fluid that could dilute or contaminate the sample

    The first drop contains tissue fluid released when the skin is punctured, which dilutes the blood sample and can alter test results; it must be discarded.

  3. The correct order of draw for capillary specimens collected in micro-collection tubes is:

    Answer: Blood gases → EDTA → other additive tubes → serum tube

    Capillary order of draw begins with blood gas specimens (if collected), then EDTA (lavender/pink) first to ensure accurate hematology results, then other additive tubes, then serum tubes last.

  4. What is the maximum recommended depth of a heel puncture in a full-term neonate?

    Answer: 2.0 mm

    CLSI recommends a maximum lancet depth of 2.0 mm for full-term neonates to avoid penetrating the calcaneus (heel bone) and causing osteomyelitis.

  5. Which area of the neonatal heel is the CORRECT site for a heelstick?

    Answer: Medial or lateral plantar surface of the heel

    CLSI guidelines specify the medial or lateral plantar surface of the heel as safe sites, avoiding the posterior curve and center where the calcaneus is close to the surface.

  6. Warming the fingertip or heel before a capillary puncture primarily serves to:

    Answer: Increase local blood flow (arterialization) for adequate sample collection

    Warming vasodilates local capillaries and increases blood flow up to 7-fold, making sample collection easier and improving the quality of arterialized capillary blood.

  7. A phlebotomist performs a fingerstick and squeezes the finger excessively to obtain enough blood. This practice can cause which test result to be FALSELY ELEVATED?

    Answer: Potassium

    Excessive squeezing (milking) causes cell lysis and release of intracellular potassium, and introduces tissue fluid—both of which falsely elevate potassium in the sample.

  8. In capillary puncture, the lancet should be positioned perpendicular to the fingerprint lines. Why?

    Answer: To ensure the wound opens freely and blood flows more easily

    Puncturing perpendicular (across) the fingerprint lines allows the wound to gape slightly and blood to flow freely; puncturing parallel to the lines tends to seal the wound shut.