Domain 7.4Phlebotomy

Capillary Puncture

Last updated June 16, 2026

Overview

A capillary puncture (dermal/skin puncture) collects a small blood sample by pricking the skin. It is essential for infants, point-of-care testing (glucose), and patients with difficult venous access.

1. Site Selection

Adults and Children (> 1 Year)

  • Site: Middle or Ring finger of the non-dominant hand.
  • Location: Fleshy, lateral (side) portion of the fingertip. Puncture perpendicular to fingerprint lines.
  • Avoid: Index finger (calloused/sensitive), Pinky (tissue too thin), Center of finger (bone too close).

Infants (< 1 Year)

  • Site: Heel Stick.
  • Location: Medial or Lateral plantar surface (outer edges) of the heel.
  • CRITICAL: Do NOT use the back of the heel or the arch. The calcaneus bone is too close, risking osteomyelitis (bone infection).

2. The Procedure

  1. Increase Blood Flow:
    • Warm the Site: Use a warmer for 3-5 minutes to cause vasodilation.
    • Use Gravity: Keep the patient's hand below the level of the heart. This helps blood flow to the fingertips naturally.
  2. Cleanse: Use alcohol and Allow to Air Dry. Wet alcohol stings and causes hemolysis.
  3. Puncture: Use a sterile lancet.
  4. Wipe Away the First Drop:
    • Why? The first drop is contaminated with tissue fluid and alcohol. Using it yields inaccurate results.
  5. Collect Sample: Apply gentle pressure.
    • Do NOT "Milk" the Finger: Aggressive squeezing causes hemolysis and mixes tissue fluid into the specimen.
  6. Order of Draw (Capillary): Different from venipuncture!
    • EDTA (Lavender) is FIRST to prevent microclots.
    • Other additives follow.
    • Serum tubes are last.

3. Special Considerations: Newborn Screening

  • Purpose: Genetic/metabolic testing (e.g., PKU).
  • Timing: Collected via heel stick 24-72 hours after birth.
  • Technique: Completely saturate the circles on the filter paper card. Do not layer drops.

4. Final Key Takeaways

  • Infant vs. Adult: Heel for infants (prevent bone injury); Middle/Ring finger for adults.
  • Safe Zone: Lateral (sides) of finger or heel.
  • Flow: Warm the site and keep the hand below the heart (gravity).
  • First Drop: Always wipe it away (removes tissue fluid).
  • Technique: No milking (causes hemolysis).