3 Capillary Blood Collection

When capillary collection is appropriate

Capillary collection obtains a small specimen through a skin puncture. It may be useful when only a small volume is needed or venous access is difficult, but it cannot provide the volume required for many tests. Capillary results may differ from venous results, so use this method only when the test and laboratory permit it.

Selecting a safe puncture site

Choose a Puncture site according to the patient’s age and size, while also considering clinical judgment and local policy. Weight, development, lancet depth, and test requirements can affect site selection. Heel puncture is usual from birth to about 6 months, with finger puncture for older children, but these are guides rather than substitutes for judgment or policy.

• Adults and older children: Usually use the fleshy side of the distal pad of the middle or ring finger. Puncture across, not parallel to, the fingerprint ridges. Avoid the thumb, index finger, and little finger.

• Infants and young children: Usually use the medial or lateral plantar surface of the heel. Avoid the center and back curve of the heel, where bone is closer to the skin. Do not puncture a newborn’s fingers.

Avoid sites that are swollen, infected, bruised, scarred, cold, or recently punctured.

Equipment and preparation

Prepare the required test request and patient-identification materials; gloves and any other protective equipment required by standard precautions; an approved, single-use safety lancet suited to the patient and site; alcohol prep and sterile gauze; the correct microcollection tubes or newborn-screening filter-paper card; and a sharps container. Use the puncture device and collection containers specified by the laboratory.

Collection sequence and technique

1. Identify and prepare the patient. Confirm the patient using the required identifiers, match the order to the requested tests, explain the procedure, and assemble the correct collection devices. Position and support the patient safely. For a child, use an age-appropriate comforting hold with a caregiver when appropriate.

2. Choose and prepare the site. Select an appropriate site and lancet depth. Warm a cool infant heel gently if needed, following local procedure. Clean the site with the approved antiseptic and allow it to dry completely.

3. Puncture once. Make a quick, deliberate puncture with a sterile, single-use lancet. Do not reuse a lancet or repeatedly puncture the same spot. Wipe away the first drop, which may contain tissue fluid or surface debris.

4. Collect in capillary order. When multiple specimens are required, collect hematology specimens first, followed by chemistry and then blood-bank specimens. This is not the venipuncture tube order. Tube colors and test-specific requirements vary, so follow the laboratory’s current microcollection instructions, especially for special tests such as blood gases. If several tubes or a larger volume are needed, ask whether venipuncture is more suitable.

5. Let blood flow freely. Allow a rounded drop to form and collect it with the appropriate microcollection device. Gently massage toward the site if needed, but do not milk, scrape, or squeeze the finger or heel forcefully: tissue-fluid contamination and hemolysis can affect results. Avoid introducing air bubbles where the test or collection device does not permit them.

6. Mix and finish. Fill containers to the required amount and mix additive tubes as directed by the manufacturer or laboratory. Apply clean gauze and steady pressure until bleeding stops, and check the site before leaving the patient. Dispose of the lancet immediately in a sharps container.

Specimen labeling and handling

Label each specimen at the point of collection according to laboratory policy, using the required patient identifiers and collection details. Check that the container is correctly filled, closed, and mixed when required; protect it from contamination; and send it promptly under the test’s transport and storage requirements. Do not assume every capillary specimen can be held or transported in the same way.

For newborn dried-blood-spot screening, use the designated card and follow the program’s instructions. Let a large drop soak into each printed circle in a single application. Do not touch the card to the skin or layer additional blood onto a partly filled spot. Dry and submit the card as instructed by the screening program; drying and delivery requirements are program-specific.

Age-appropriate technique and safety

Technique and site choice must be adapted to age and the patient’s circumstances.

• Infants: Use the medial or lateral plantar heel and an age-appropriate lancet. Warm the heel gently if needed and position the infant securely but calmly. Excessive compression or puncture depth can injure tissue or bone.

• Older children: Choose heel or finger based on age, size, development, and local guidance. Explain the steps simply, offer reassurance, and stabilize the hand or foot before puncturing.

• Adults: The middle or ring finger is generally preferred. Support the hand and avoid areas with poor circulation or damaged skin.

• All ages: Use standard precautions, one sterile lancet per puncture, and firm pressure afterward. Follow institutional limits on collection attempts and seek assistance if unsuccessful.