Capillary Blood Collection: Heel Stick & Finger Stick Procedures

Capillary blood collection is essential for neonates, infants, and pediatric patients when venipuncture is not feasible. Master the heel stick and finger stick procedures, and you will be confident collecting from the most challenging patient populations.

When to Use Capillary vs. Venipuncture

Capillary Collection Is Preferred For:

• Neonates (0-7 days old): Heel stick is the standard of care. Venous puncture is rarely attempted due to tiny vessel size.
• Infants (7 days-2 years): Heel stick for sampling
• Pediatric patients (2-12 years): Finger stick acceptable if cooperation is possible. Heel stick if child cannot cooperate.
• Adults with difficult veins: Finger stick if venipuncture is unsuccessful after 2 attempts and urgent testing is needed.
• Burn victims or patients on anticoagulation: Capillary collection reduces bleeding time compared to large-bore venipuncture.

Venipuncture Is Preferred For:

• Microorganism cultures (blood cultures): Venipuncture is sterile; capillary sticks carry higher contamination risk from skin flora.
• Large-volume samples: Venipuncture is much faster and yields larger volumes.
• Coagulation studies: Light blue tubes require precise 9:1 blood-to-citrate ratio, which is difficult to achieve with capillary collection.

Neonatal Heel Stick Procedure (CLSI H04 Standard)

Approved Heel Stick Sites

The heel is the only approved site for neonates. Specific zones on the plantar surface (bottom of the heel) are safe; others risk nerve and artery damage.

• Medial plantar surface (inner side): SAFE. Start from the midline and extend toward the inside of the foot. This is the preferred zone.
• Lateral plantar surface (outer side): SAFE. From the midline toward the outside of the foot. Secondary preferred zone.
• Posterior heel (back): AVOID. Risk of puncturing the calcaneal artery (posterior tibial artery runs here).
• Anterior heel (front, near toes): AVOID. Risk of nerve damage (plantar nerve runs here).

Visual rule: Imagine a vertical line down the middle of the heel (from middle of big toe to middle of heel). Stay lateral to this line on the medial side OR lateral to this line on the outer side. Never go posterior.

Heel Stick Depth and Needle Selection

Maximum penetration depth: 2.0 mm

Why: Neonatal heels are thin. Penetrating deeper than 2.0 mm risks hitting bone (calcaneus), blood vessels, or nerves.

Lancet selection: Use a 2.0 mm or smaller lancet designed for neonatal use. Many facilities use automated safety lancets (e.g., Tenderfoot, Quikeel) that control depth precisely to 2.0 mm.

Step-by-Step Heel Stick Procedure

1. Warm the heel: Apply a warm (not hot) compress or heat pad to the heel for 3-5 minutes. Warming increases capillary blood flow 5-7 fold and ensures adequate sample volume. Temperature should be
2. Cleanse the site: Use 70 percent isopropyl alcohol or chlorhexidine on a sterile pad. Use circular motions, working outward from the intended puncture site. Allow to air dry completely (do not blow or fan).
3. Position the foot: Hold the infant foot firmly but gently, with the heel accessible and downward (gravity aids blood flow).
4. Palpate the site: Use your finger to identify a safe site in the medial or lateral plantar area. Mark mentally; do not mark with pen (pen ink can be ingested if infant brings foot to mouth).
5. Insert the lancet: Hold the lancet at 90 degrees (perpendicular) to the skin surface. Use a swift, confident motion to penetrate 2.0 mm. This should be one smooth motion, hesitation increases pain and tissue damage.
6. Discard the first drop: Wipe away the first drop of blood with sterile gauze. The first drop contains tissue fluid and skin cells, which can falsely elevate glucose, potassium, and other analytes. CLSI H04 requires this step.
7. Collect capillary tubes: Allow subsequent drops to fill capillary tubes by gentle contact. Do NOT squeeze the heel excessively, this drives tissue fluid into the capillaries and contaminates the sample. Let blood flow naturally.
8. Order of collection: Fill tubes in this order: (1) Lavender (EDTA) for hematology, (2) Gold/SST for chemistry, (3) Heparinized tubes for other chemistry, (4) Special capillary tubes for blood banking or testing. This minimizes additive carryover (though carryover is less of an issue in capillary than venipuncture).
9. Apply pressure: After collection, apply firm pressure to the site with sterile gauze for 1-2 minutes until bleeding stops. An infant clotting may take longer than an adult.
10. Bandage: Apply a sterile adhesive bandage sized for the infant (small bandage, not adult-size). Ensure it cannot be pulled off and ingested.

Heel Stick Troubleshooting

Inadequate blood flow after warming: Re-warm for another 2-3 minutes. Some infants have poor peripheral circulation. Avoid aggressive squeezing, it contaminates the sample.

Excessive bleeding: Hemophilia or coagulopathy. Apply pressure for 3-5 minutes. Call pediatrician if bleeding does not stop.

Crying/distress: Normal in infants. Continue collection. Comfort after, not during, to maintain focus.

Finger Stick Procedure (Pediatric & Adult)

Approved Finger Sites

Preferred sites: 3rd and 4th fingers (middle and ring fingers)

Acceptable sites: 2nd and 5th fingers if 3rd and 4th are unavailable (callused, bandaged, or infected)

Surface selection: Lateral (side) surface of the finger, NOT the fingertip. The fingertip has more nerve endings and causes more pain. The lateral surface has better capillary blood flow and is less sensitive.

Avoid: Thumb (thick keratin layer, hard to penetrate), index finger (callused from writing), pinky (too much bone, too little tissue), fingers with recent punctures or infections.

Step-by-Step Finger Stick Procedure

1. Warm the finger: Ask the patient to warm their hands or apply a warm compress for 2-3 minutes. Alternatively, have them swing their arm in a windmill motion (centrifugal force increases blood flow to fingertips).
2. Select the site: Choose the 3rd or 4th finger, lateral (outer) surface, midway between the tip and the knuckle.
3. Cleanse the site: Use 70 percent isopropyl alcohol on a sterile pad, working in circular motions. Allow to air dry completely.
4. Palpate: Gently press the site to ensure good blood flow. If skin is very pale or cool, re-warm.
5. Insert the lancet: Hold at 90 degrees perpendicular to the skin. Use a swift, confident motion. Depth is typically 2-3 mm for adults (slightly deeper than heel sticks, since fingers are less delicate).
6. Discard the first drop: Wipe away with sterile gauze. Always discard the first drop, CLSI H04 applies to all capillary collection, not just heel sticks.
7. Collect capillary tubes or spots: For glucose testing, let blood drop onto a glucose meter or test strip. For capillary tube collection (micro-hematocrit, small chemistry samples), allow blood to fill tubes by gentle contact (do not squeeze).
8. Apply pressure: After collection, apply firm pressure with sterile gauze for 1-2 minutes.
9. Bandage: Optional for adults; usually not necessary if bleeding has stopped. For pediatric patients, a small bandage provides comfort and prevents re-bleeding.

Special Technique: Finger Stick for Glucose Testing

Glucose testing is the most common finger stick procedure:

• Glucose meters are sensitive to cold: If the patient hands are cold, glucose readings are falsely low by 5-10 percent. Warm hands before collecting.
• Avoid alcohol residue: Allow alcohol to air dry completely. Residual alcohol can dilute the blood drop and falsely lower glucose.
• Do not squeeze: Let blood flow naturally. Squeezing dilutes the sample with tissue fluid and falsely lowers glucose readings.
• Adequate volume: Most meters require 0.3-0.5 μL of blood. A drop the size of a small pearl is usually adequate. Check your meter requirements.

Order of Collection for Capillary Tubes

When drawing capillary samples for multiple tests, follow this sequence to minimize cross-contamination:

1. Lavender (EDTA) for hematology or blood banking
2. Green (heparin) for chemistry or plasma studies
3. Gold (serum separator) for chemistry
4. Red (plain) for serology
5. Blue (citrate) for coagulation (rarely done via capillary; limited sample volume)

Practical note: Most capillary collections are for a single test (glucose, hematocrit, or hemoglobin), so full multi-tube order is rarely needed. If multiple tests are ordered, check your lab protocol for tube order.

First Drop Discard: Why It Matters

The first drop of blood from any capillary puncture contains:

• Tissue fluid (plasma that leaked during puncture)
• Epithelial cells and debris
• Skin flora (bacteria)

This contamination falsely elevates:

• Glucose (tissue glucose oxidase interference)
• Potassium (leakage from damaged cells)
• Hemoglobin/hematocrit (cell debris)

CLSI H04 mandate: Always discard the first drop. No exceptions. This is a quality and accreditation requirement.

Special Populations

Premature Infants (

Heel stick is still acceptable, but use

Infants with Osteomyelitis or Septic Arthritis of the Foot

Avoid heel stick entirely (risk of spreading infection). Use finger stick or venipuncture if possible.

Patients with Severe Anemia or Thrombocytopenia

Capillary collection is acceptable but may result in slower blood flow. Allow extra time for filling capillary tubes. Apply pressure longer to stop bleeding (2-5 minutes).

Summary: Key Takeaways

• Neonates: Heel stick only (medial or lateral plantar surface, never posterior). Maximum depth 2.0 mm.
• Infants and children: Heel or finger stick depending on cooperation and age. Finger stick preferred for older children.
• Always warm the site first (3-5 minutes for heels, 2-3 minutes for fingers).
• Always discard the first drop (CLSI H04 requirement).
• Never squeeze excessively (dilutes sample with tissue fluid).
• Apply pressure for 1-2 minutes after collection to stop bleeding.
• Order of collection: EDTA, heparin, gold/SST, red, blue (if needed).

Master these procedures and you will be the go-to phlebotomist for pediatric and neonatal collections in your facility.