SOP-P-003 — Capillary (Skin Puncture) and Neonatal Heel-Stick Blood Collection Procedure SOP

1.0 Purpose

This SOP gives the bench procedure for collecting diagnostic capillary blood specimens by skin puncture, for neonatal heel sticks, pediatric finger sticks, and adult micro-sampling. It covers accurate device selection, controlled penetration depth, the correct microtainer order of draw, bedside labeling, and patient safety.

2.0 Scope

This SOP applies to all capillary blood sampling by authorized Medical Technologists and trained patient-care personnel for tests within TCH scope (such as complete blood count, blood film evaluation, bedside glucose, and micro-volume chemistry), in inpatient wards and outpatient areas. Venous sampling is covered in Adult and Pediatric Venipuncture Procedure Sop.

3.0 Definitions

• Capillary Blood: Blood obtained through skin puncture, composed of physiological mixtures of arteriolar, venular, and capillary blood along with interstitial and intracellular fluids.
• Heel-Stick: Controlled skin incision on the plantar surface of an infant's heel using an automated safety lancet.
• Calcaneus: The heel bone of an infant; vulnerable to osteochondritis or osteomyelitis if incision depth exceeds safe anatomical margins.
• Micro-Collection Tube (Microtainer): Small-volume collection tube (250–500 µL) containing spray-dried anticoagulant or separator gel specifically designed for capillary blood.
• Milking: Repetitive, forceful squeezing or stripping of adjacent tissue around a puncture site, prohibited because it causes hemolysis and tissue-fluid dilution.

4.0 Responsibility

4.1 Hospital Director

• Approves this procedure and ensures safety-engineered, auto-retractable incision devices are available.

4.2 Pathologist

• Reviews this procedure for clinical adequacy and sets the micro-sample limitations for specific diagnostic tests.

4.3 Chief Medical Technologist / Laboratory Quality Manager

• Maintains version control, reviews capillary quality indicators (hemolysis, microclots, QNS rates), and audits staff compliance.
• Ensures all collecting personnel have documented training and competency assessment in skin puncture and heel-stick techniques.

4.4 Medical Technologists

• Verify patient identity with two independent identifiers and confirm request details before puncture.
• Select the proper anatomical site, device, and penetration depth for the patient's age and physical development.
• Collect blood without milking the tissue, follow the capillary order of draw, and label containers at the bedside.

4.5 Laboratory Aides

• Clean collection trays, stock microtainers, and prepare warming compresses under technologist direction.
• Help comfort infants and stabilize pediatric limbs during collection.
• Shall not perform skin puncture, select lancets, or manipulate exposed incision devices.

4.6 Patient Care Area Personnel (Nursing)

• Coordinate ward patient timing, give the neonatal clinical history, and help with infant holding.

5.0 Policy / Procedure

5.1 Clinical Indications for Capillary Collection

• Capillary collection is indicated when: - The patient is an infant or small child where venipuncture presents excessive trauma or difficulty. - Adult patients present with severe burns, extreme obesity, thrombotic tendencies, or severe venous fragility. - Only a small volume of blood is required and the analytical method is validated for capillary specimens (such as CBC, smear, or POCT glucose).
• Capillary blood is contraindicated when the patient is severely dehydrated, in shock, has marked peripheral edema, or requires large blood volumes (>1–2 mL) for multiple diagnostic tests.

5.2 Device Selection and Penetration Depth

Use only single-use, auto-disabling safety lancets with pre-set retraction mechanisms. Reusable lancets or manual surgical blades are prohibited:

5.3 Anatomical Site Selection and Landmarks

• For infants under 1 year of age, perform heel puncture strictly within the medial or lateral plantar borders of the heel: - Puncture within the medial safe zone (medial to an imaginary line drawn posteriorly from the middle of the great toe to the heel) or the lateral safe zone (lateral to an imaginary line drawn posteriorly from between the fourth and fifth toes to the heel). - Never puncture the posterior curvature of the heel (bone is only 1–2 mm beneath the surface), the central plantar arch (risk of tendon and nerve injury), previous puncture sites, or areas showing edema or bruising.
• For children over 1 year of age and adults, perform finger puncture on the fleshy palmar surface of the distal phalanx of the middle (3rd) or ring (4th) finger: - Place the puncture slightly off-center of the fleshy pad, oriented perpendicular to the epidermal ridges (fingerprint whorls) to facilitate drop formation. - Never puncture the fifth (little) finger (tissue depth is inadequate), thumb, index finger (calloused or hypersensitive), side or edge of the finger, or earlobes.

5.4 Pre-Puncture Preparation and Warming

• Confirm patient identity using at least two independent identifiers (full name and hospital MRN) with the patient or parent/guardian.
• Instruct a second staff member or parent on holding the child's foot or hand securely and comfortably to prevent sudden withdrawal during puncture.
• If the extremity is cool or poorly perfused, apply a warm, moist towel or warming compress (temperature not exceeding 42 °C) to the site for 3–5 minutes. Warming increases arterial blood flow up to sevenfold without altering hematological values.
• Cleanse the site with a 70% isopropyl alcohol pad using gentle friction. Allow the skin to air-dry completely for 30 seconds; residual alcohol causes stinging, cellular hemolysis, and prevents round drop formation. Do not use povidone-iodine, as iodine contamination falsely elevates potassium, phosphorus, and uric acid results.

5.5 Puncture and Collection Technique

• Hold the infant's heel or patient's finger firmly, and position the safety device against the sanitized skin at the chosen landmark.
• Trigger the device so the blade automatically incises the tissue and immediately retracts into the housing. Discard the used device directly into the point-of-use sharps container.
• Wipe away the first drop of blood firmly with a sterile dry gauze pad; the first drop contains excess intracellular fluid and tissue thromboplastins that compromise test accuracy and trigger premature clotting.
• Allow a large, rounded drop of blood to form naturally at the incision site.
• Position the collection scoop of the microtainer directly underneath the drop, allowing blood to flow smoothly down the interior wall of the tube.
• Apply gentle, intermittent pressure to the surrounding tissue. Do not milk, squeeze, or scrape the skin with the tube edge, as this lyses erythrocytes and introduces tissue fluids.
• A single collector shall perform no more than two skin punctures per patient encounter. If sufficient blood is not obtained after two attempts, notify the Chief Medical Technologist / Laboratory Quality Manager and follow the escalation protocol in Phlebotomy Workflow Unacceptable Specimens and Adverse Reactions Sop.

5.6 Capillary Order of Draw

To avoid microclot formation in hematology tubes from activated platelets, collect microtainers in the following mandatory sequence:

Note: EDTA microtainers must be collected first and inverted immediately to maintain cell suspension integrity.

5.7 Post-Puncture Hemostasis, Bedside Labeling, and Transport

• Press a clean, sterile gauze pad firmly against the puncture site until bleeding has completely ceased (typically 1–2 minutes). For children aged 2 years and older, apply an adhesive bandage. For infants and children under 2 years of age, do not apply adhesive tape or bandages (to avoid skin excoriation and accidental choking hazards); ensure complete hemostasis before release.
• Affix the printed or clearly handwritten label to each microtainer at the bedside immediately after collection. Ensure the label specifies: Patient Full Name, Hospital MRN, Collection Date and Time, and Collector Initials. Note "Capillary" as the specimen source.
• Place sealed microtainers upright in a designated rack or transport container and deliver immediately to the laboratory workstation per Specimen Handling Packaging Transportation Policy.

6.0 Records

7.0 References

• DOH Clinical Laboratory QMS Tool, Section 3 — Service Delivery
• DOH Administrative Order No. 2021-0037, Annex B1 — Technical Standards for Clinical Laboratories
• ISO 15189:2022, Section 7.2 — Pre-examination Processes
• WHO Guidelines on Drawing Blood: Best Practices in Phlebotomy (2010)
• CLSI GP42, Procedures and Devices for the Collection of Diagnostic Capillary Blood Specimens

Companion policies:

• Specimen Collection Policy — Laboratory-wide specimen collection rules and order of draw
• Adult and Pediatric Venipuncture Procedure Sop — Diagnostic adult and pediatric venipuncture procedure
• Laboratory Retention Schedule Policy — Master retention schedule for phlebotomy records and requisitions