Chapter 9: Capillary Puncture & Related Procedures

Vocabulary flashcards covering equipment, procedures, sites, and tests associated with capillary puncture and capillary blood collection.

Capillary Puncture

A skin puncture technique used to obtain a capillary specimen composed of arterial blood (greater portion), venous blood, and interstitial fluid.

Indications for Capillary Puncture

• Difficult venipuncture

• need for repeat collection

• small blood volume required

• newborn screening

• fragile veins.

Capillary Specimen

Mixture of arterial, venous, and capillary blood plus interstitial and intracellular fluid.

Lancet

Sharp, pointed instrument that punctures the skin; depth ≤2 mm for children, ≤3 mm for adults.

Puncture Site (Finger)

Always lateral side of the distal segment of the middle or ring finger on the non-dominant hand.

Sites to Avoid (Finger)

Index finger, thumb, pinky, finger tip center, or side of a mastectomy.

Heel Stick Site (<1 year)

Plantar surface of the heel—medial to an imaginary line from the great toe or lateral to a line between 4th & 5th toes.

Calcaneus Warning

Calcaneus bone lies ~2 mm below heel skin; hitting bone risks osteomyelitis or osteochondritis.

Microcollection (Microtainer) Tube

Small plastic tube, color-coded like venous tubes, filled by capillary action or from a syringe.

Microhematocrit Tube

Plastic capillary tube (50-75 µL) coated with ammonium heparin (red) or none (blue) for hematocrit/PCV tests.

Sealant (Clay)

Plastic clay used to seal one end of a microhematocrit tube before centrifugation.

Warming Device

Heats the puncture area to raise blood flow up to seven-fold, ensuring adequate sample volume.

Capillary Blood Gas (CBG) Collection Tube

Narrow, 100 mm tube holding ~100 µL; color band indicates anticoagulant presence.

Stirrer

Small metal bar inserted into CBG tube to mix blood and anticoagulant.

Magnet

Used externally to move the metal stirrer and mix the specimen.

Plastic Cap

Cap placed on CBG tube to maintain anaerobic conditions.

• Phenylketonuria

• cystic fibrosis

• galactosemia

• Congenital hypothyroidism

Common Neonatal Screenings

• Blood smears

• neonatal screening

• blood gases

• CBC

• electrolytes

• point-of-care tests

• neonatal bilirubin.

Frequent Capillary Tests

Capillary Order of Draw

1) Blood gases

2) EDTA

3) Heparin (green)

4) Other additives

5) Serum (red or gold).

Most Important Part of Capillary Puncture

Always wipe away the first drop of capillary blood before collecting for a smear.

Spreader Slide Angle

Hold the spreader slide at a 30–35° angle.

Slides must have…

No Clots

No Bubbles

Feathered Edge: The thin, tapered end of a blood smear.