Blood Collection via Capillary Puncture in Infants
The Heel Stick
The areas of the bottom surface of the newborn's heel contain the best capillary bed and provide protection against damaging the calcaneus. Therefore a heel stick is the preferred method to collect a blood sample from neonates and infants under 6 months of age because their fingers are too small. When choosing the puncture site care should be taken not to select a site that has already (recently) been punctured before.
The puncture should be made on the flat bottom surface of the foot, not on the posterior curvature of the heel where the heel bone (calcaneus) is very close to the skin surface. Sticking an infant straight into the medial aspect of the back of the heel could cause damage to nerves, the bone, or infection to this sensitive area.
Drawing Blood from an Infant's Heel
The National Committee for Clinical Laboratory Standards (NCCLS) recently made a change in the standards regarding heel sticks in infants. The depth of an infants heel skin puncture should not exceed 2 mm to avoid hitting a bone (changed from 2.4 mm). Beside protecting the calcaneus, this depth is adequate to reach the capillary beds and provide sufficient blood flow to collect the sample. Most experts warn specifically against the use of a surgical blade of any kind for heelstick because of the danger of a deep puncture, infection, and damage to the infant's calcaneus.
A full-color chart illustrating proper specimen collection, "Neonatal Screening Blood Specimen Collection and Handling Procedure," may be obtained at no charge from Schleicher & Schuell, Inc., P.O. Box 2012, Keene, NH 03431; 1-800-245-4024; FAX 603-357-7700.
Preparing the heelstick site and drawing blood as follows:
The equipment needed for the heelstick is a sterile 2 mm lancet, sterile alcohol prep, sterile gauze pads, soft cloth, blood collection form, blood collection tube or dry blood spot paper, gloves. Do not contaminate filter paper circles by touching them or by spilling liquids on them before or after blood collection.
Warm the heel for 3 minutes prior to puncture by using "heel warmers" for neonates which are very safe to use, or if not available, by wrapping a moist warm wash cloth up to 41°C. Moist heat helps to increase blood flow to the area to be punctured. The increase in blood flow has been found to be as much as sevenfold. The blood specimen must be collected immediately after the 3 minute warming, because the wash cloth will rapidly cool the heel as it cools and this will actually slow the blood flow
As with fingersticks and venipunctures, it is important to cleanse the puncture site. High risk newborns are especially prone to infection. The antiseptic should remain in contact with the skin for at least 1 minute and should be rubbed off with a dry, sterile swab. If the site is not dried well, the antiseptic can mix with the specimen and the blood will not "bead up" well at the puncture site. Rather, the blood will spread over the moist area, making it difficult to collect.
Thoroughly scrub your hands and arms to the elbow with soap and water, and put on disposable gloves.
Positively identify the infant!!!!
Thoroughly cleanse the plantar surface of the foot with 70% alcohol, then dry the alcohol scrub area with sterile gauze. NOTE: Vigorous scrubbing of the entire foot bottom helps promote circulation near the skin surface.
Place neonate on stomach if possible and place his/her limb lower than the level of the heart to increase blood flow to the foot.
Perform a swift, clean puncture on the plantar surface of the heel at a 45-60 degree angle. NOTE: The "crown" portion of the heel should not be used. It is too close to the calcaneus.
Wipe away the first drop of blood.
Gently and progressively squeeze the lower leg and ankle using a "tennis racket" grip.
Place a sterile gauze over the puncture site after collection until the puncture wound seals. Occasionally, a small bandage is required, but should not be used unless absolutely necessary because of the sensitive nature of neonatal skin. Never apply a bandage to an older baby or toddler's injection site because there is a danger of pulling it off and swallowing it!
Watch for any signs of distress from the patient that are unusual or appear to impair cardiopulmonary function. Be careful not to displace any lines or monitoring devices attached to the patient!
Discard contaminated materials properly
Label specimen cards or tubes correctly
Lancets for Capillary Puncture
A wide variety of lancets are available for capillary puncture. Unfortunately, none are exactly the right length and width to provide a puncture of 2 mm deep and 2.0-2.5 mm in length for a heelstick. Therefore, most experts recommend use of lancets of the correct length which are designed with guards to prevent deep punctures, although in most the width of the lancet is not ideal either. One lancet, however, designed for heel sticks on infants and premature babies that is exemplary for safety and ease of use is the BD Quikheel® Safety Lancet. You can read usage tips and view a video here.
*Quikheel is a registered trademark of Becton, Dickinson and Company.