Good advice for drawing blood from infant heels
by Dennis Ernst • September 07, 2020
Most phlebotomists dread having to draw newborns. No one wants to cause such a small, fragile human being pain. To treat and prevent illness, however, it’s a necessary discomfort. What isn’t necessary, however, is when we have to restick a newborn because of improper technique or errors in the process. Unfortunately, many babies experience multiple heelsticks. Poor blood flow can be caused by many factors, but knowing how to maximize the volume of blood from a heelstick is critical to minimizing the number of repeat punctures. So, naturally, the best way to reduce repeat heelsticks is to obtain a suitable specimen the first time. By being attentive and vigilant, we can eliminate unnecessary and painful repeat heelsticks for our smallest patients.
Gravity is your friend
How specimen collection personnel position the infant can make a significant difference in how easily the specimen is obtained. If possible, position the infant so that the foot is on a plane lower than the heart. This can be accomplished by elevating the head of the bassinet or car seat (for outpatient draws) slightly. Before making such an adjustment, however, check to see if the baby’s crib or car seat accommodates such repositioning, and that you are permitted to do so by facility policy. Additionally, keeping the foot as low as possible throughout the collection can help the capillary beds fill more quickly and completely making an adequate volume of specimen easier to obtain. For outpatients held by a parent, instruct the parent to keep the baby as upright as possible throughout the procedure.
Babies tend to wiggle away from things they don’t like. Most infants will reflexively pull their foot away from stimulation. To maintain control, firmly encircle the ankle with two fingers, ensuring your grip does not restrict blood flow.
Site Selection and Equipment
The precise location you choose to puncture the heel is a very important decision. The CLSI skin puncture standard lists the medial and lateral portions of the bottom surface of the heel as acceptable.(1) Heel bones in infants are close to the surface of the skin, so the lancet should puncture less than 2.0 mm deep. Osteomyelitis is an inflammation of the bone can lead to complications and disability. CLSI also states that a previously punctured non-healed site should be avoided. The chosen site should also not be bruised, scarred, or show signs of infection.
Cleanse the site first with an alcohol prep and allow it to dry completely. Wet alcohol can cause the baby unnecessary pain when the lancet punctures the skin.
The order of draw for capillary collections is also important, and different from venipunctures. After wiping away the first drop of blood with clean gauze (to prevent tissue fluid from contaminating the sample), the EDTA tube should be collected first followed by other additive tubes. Non-additive tubes are filled last. Incorrectly placing the EDTA tube later in the order risks platelet clumping, a natural occurrence when skin is punctured. Since this process is not immediate, the first tube filled is less likely to contain clumped platelets than later tubes. Because the EDTA tube is the one used to count platelets as part of the complete blood count (CBC), filling it first increases the lab’s ability to provide the physician with an accurate platelet count.
To ensure proper mixing, gently invert all additive tubes 5-10 times according to the tube manufacturer’s recommendations. One inversion is defined as upending the tube, then returning it to an upright position. Each time the tube is overturned, make sure the contents flow to the opposite end before uprighting so the additive mixes well with the sample. EDTA tubes are especially prone to clotting during sample collection, so it is prudent to gently tap the tube on a hard surface to agitate the sample during collection.
Quantity and Quality
Use only gentle pressure to ease blood from the puncture site. If the site was prewarmed, gentle pressure should be all that's necessary for a consistent and adequate flow. After collecting the drop, release the pressure applied to the site and give the capillary bed time to refill. If you find you are constantly squeezing and “milking” the foot to obtain enough blood, be aware that you are likely hemolyzing the specimen and contaminating it with tissue fluid. It’s also painful to the infant. If excessive squeezing is required, you should terminate the collection. The likelihood that the specimen will render accurate results decreases proportional to the force squeezing the heel. To make milking unnecessary, prewarm the heel with a warm compress not to exceed 42-degrees Celsius. The flow of blood through the capillary beds will be seven times more than that through sites that have not been prewarmed. The result: an adequate flow of blood into the collection tube with minimal or no squeezing.
If the device you use incorporates a scoop into its design, CLSI recommends the device not be scraped across the puncture site in an effort to force blood to the opening. Forceful scooping is also painful to the patient and forces tissue fluid into the sample.
Before terminating the draw, make sure the collection meets minimum fill requirements. Short samples cheat the patient out of an accurate test result, and often force testing personnel to request the specimen be recollected. Fill all tubes to their stated volume every time. Some specimens require special handling during and/or immediately after collection. Make sure you are prepared to protect light-sensitive specimens from exposure using amber light-blocking tubes or a light-tight wrap. If the specimen is to be immediately chilled, have an ice slurry available before you begin the procedure. Any delay or improper handling could force the laboratory to request a recollection due to the potential for a mishandled specimen to produce erroneous results.
Babies have it rough enough coming into the world. Unnecessary repeat collections only cause additional trauma. Those who draw their blood properly and compassionately can have a significant impact in making their new world a more welcoming place.
1. CLSI. Collecting Capillary Blood Specimens: Approved Standard - Seventh Edition. GP42-A7 Wayne, PA, 2020.
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