Blood is drawn from infants using two main approaches: a heel stick for capillary samples and venipuncture for venous samples, with the choice depending on the baby’s age, size, and which tests are needed. The heel stick is far more common in newborns and young infants because it requires less technical skill and yields enough blood for routine screening, but the two methods are not interchangeable. They produce measurably different lab results, carry different risks, and call for different pain-management strategies.
The Heel Stick and Why It Dominates Newborn Blood Collection
If your baby has had blood drawn in the first days or weeks of life, it was almost certainly taken from the heel. Heel pricks are the standard method for capillary blood sampling in neonates and infants, used for everything from the newborn metabolic screening panel to bilirubin checks and blood glucose monitoring. The procedure targets the outer edges of the heel, avoiding the center where nerves and the calcaneus bone sit closer to the surface. A small blade or spring-loaded device punctures the skin, and the collector gently squeezes blood into a tiny tube or onto a filter-paper card.
The devices used for this have improved considerably. Older manual lancets required the practitioner to control puncture depth by hand, which led to inconsistent cuts and more tissue damage. Automated incision devices produce a controlled, uniform cut. A comparative study of heel-stick devices found that automated incision devices yielded significantly more blood in less time and produced less hemolysis, the rupturing of red blood cells that can compromise sample quality.1JAMA Network (American Medical Association). A Comparative Study of Heel-stick Devices for Infant Blood Collection A later study evaluating a spring-loaded blade device found that babies grimaced less, cried for a shorter time, and were far more likely to need only a single puncture compared with those stuck by a standard manual lancet.2JAMA Network. Evaluation of a New Lancet Device (BD QuikHeel) on Pain Response and Success of Procedure in Term Neonates
Even with better devices, technique matters. If the person collecting blood squeezes the heel too hard to coax out drops, the sample can become contaminated with tissue fluid, which artificially raises potassium and hemoglobin values. That kind of squeezing-related error has been documented especially in the youngest newborns.3Clinical Chemistry. Studies on the quality of specimens obtained by skin puncture of children 1. Tendency to hemolysis, and hemoglobin and tissue fluid as contaminants
Venipuncture in Infants
When larger volumes of blood are needed or when tests require a true venous sample, clinicians perform venipuncture, inserting a small needle into a vein. In neonates and infants, the available veins are tiny and often hard to see, so practitioners may use sites that would be unusual in adults. Scalp veins, the veins on the back of the hand, and the great saphenous vein along the inner leg are all commonly used access points.4PubMed Central. Peripheral Venipuncture in Pediatric Patients: A Mini-Review of Clinical Practice and Technological Advances Scalp veins, while startling for parents to see, are relatively superficial and can be easier to access in very small babies than veins in the arms or legs.
First-attempt success rates for infant venipuncture can be frustratingly low with traditional methods. One technology that has shown promise is the vein finder, a device that uses near-infrared light to project an image of the veins onto the skin. A quasi-experimental study in preterm infants found that using a vein finder raised the first-attempt success rate from roughly 47% to 87%, cut the time to successful cannulation nearly in half, and reduced complications like infiltration and phlebitis.5BMJ. Comparing the effects of vein finder technology and traditional venipuncture on pain and behavioural states in preterm infants: a quasi-experimental study The evidence is not universally positive, though. A different study testing a near-infrared device in a pediatric blood-drawing center found no improvement in first-attempt success rates.6PubMed Central. Impact of near infrared light in pediatric blood drawing Centre on rate of first attempt success and time of procedure The discrepancy may come down to population differences, since finding veins in preterm infants is a harder problem than in older, larger children, leaving more room for a device to help.
Umbilical Artery Catheters in the NICU
For very sick or very premature babies in the neonatal intensive care unit, there is a third route: blood sampling through an umbilical artery catheter. These catheters are threaded through one of the arteries in the umbilical stump shortly after birth and sit in the aorta, providing easy access for repeated blood draws without additional needle sticks. This is critical for babies who need frequent monitoring of blood gases and other labs.
The concern with this method is not pain from puncture but rather what happens inside the baby’s brain during the draw. Withdrawing blood through a catheter sitting in the aorta can temporarily reduce cerebral blood flow and oxygenation. Research on very low birth weight infants showed that when blood was drawn quickly, within about 20 seconds, there was a significant drop in the amount of oxygenated hemoglobin in the brain. When the draw was slowed to around 40 seconds, that drop disappeared.7Pediatrics. Slow Blood Sampling From an Umbilical Artery Catheter Prevents a Decrease in Cerebral Oxygenation in the Preterm Newborn A follow-up study added nuance: the drop in cerebral oxygenation depended more on how much blood was withdrawn than on how quickly it was drawn. Reducing the sample volume blunted the effect more than simply slowing the draw speed.8Acta Paediatrica. Umbilical artery catheter blood sampling volume and velocity: Impact on cerebral blood volume and oxygenation in very‐low‐birthweight infants Based on this kind of evidence, NICU teams at institutions like the University of Iowa Children’s Hospital have changed their protocols to mandate slower withdrawal and flushing rates for umbilical artery catheter blood sampling.9PubMed Central. How fast is too fast? a practice change in umbilical arterial catheter blood sampling using the Iowa Model for Evidence-Based Practice
Managing Pain During the Procedure
Infants absolutely feel pain during blood draws, and the idea that newborns are too neurologically immature to register it was abandoned by medicine decades ago. The good news is that several simple, non-drug interventions are surprisingly effective.
The most studied is oral sucrose. A large Cochrane review found high-quality evidence that giving a small amount of sweet solution, typically about half a milliliter of 24% sucrose, before a heel lance or venipuncture meaningfully reduced pain scores in both preterm and full-term infants.10PubMed Central. Sucrose for analgesia in newborn infants undergoing painful procedures An earlier trial demonstrated the magnitude of the effect plainly: newborns who received a sucrose solution before blood collection cried about half as much during the procedure as those who received water, and they calmed down within about a minute afterward compared with two and a half to three minutes for the water group.11Pediatrics. Sucrose as an Analgesic for Newborn Infants The benefit extends to sick hospitalized infants, not just healthy newborns. A randomized trial in ill neonates confirmed that sucrose reduced both the facial pain response during the lance and crying during the recovery period.12PubMed. Oral sucrose for procedural pain in sick hospitalized infants: a randomized-controlled trial
Breastfeeding during or just before a heel stick consistently outperforms most other comfort measures. A randomized trial comparing breastfeeding, skin-to-skin contact, and swaddling with holding found that breastfeeding produced the lowest pain scores after the procedure.13PubMed Central. Comparison of different methods for reducing pain during a heel lance in newborns: a randomized trial Other research found that breastfeeding was more effective than heel warming alone for reducing both pain and calming time.14PubMed. Effects of breastfeeding and heel warming on pain levels during heel stick in neonates It likely works through a combination of sucrose in the breast milk itself, the physical comfort of being held, and the distraction of sucking.
Skin-to-skin contact, sometimes called kangaroo care, and facilitated tucking, where the baby is gently held in a curled, contained position, also reduce pain responses. One study found that facilitated tucking actually caused less crying than breastfeeding or kangaroo care, though all three were better than no intervention.15PubMed. The Effect of Breastfeeding, Kangaroo Care, and Facilitated Tucking Positioning in Reducing the Pain During Heel Stick in Neonates Parent involvement has its own benefits. A study of mothers providing gentle human touch during venipuncture found that the touched infants had higher oxygen saturation, lower pain scores, and shorter crying, while the mothers themselves reported less anxiety.16PubMed Central. The Effect of Mother’s Gentle Human Touch on Preterm Neonate’s Pain and Maternal Anxiety During Venipuncture in Turkiye
Why Topical Numbing Creams Are Not the Default
If you have ever used a numbing cream before a child’s vaccination, you might wonder why EMLA cream, the standard topical anesthetic containing lidocaine and prilocaine, is not routinely applied before infant blood draws. The answer is that it does not work particularly well for this purpose, and it carries a specific risk in newborns.
A meta-analysis of six trials involving over 700 infants found that EMLA showed little or no pain reduction compared with sucrose, breastfeeding, or even placebo.17PubMed. Efficacy and Safety of EMLA Cream for Pain Control Due to Venipuncture in Infants: A Meta-analysis On top of that, EMLA can raise methemoglobin levels, a form of hemoglobin that cannot carry oxygen. While one study in term neonates found that the increase stayed well below harmful levels after a one-hour application of a small amount of cream,18Acta Paediatrica. Methaemoglobin formation after the use of EMLA cream in term neonates a trial in healthy preterm infants found no significant pain benefit and noted higher methemoglobin concentrations eight hours after application, concluding that routine use in this population was not supported.19Archives of Disease in Childhood – Fetal and Neonatal Edition. Randomised controlled trial of eutectic mixture of local anaesthetics cream for venepuncture in healthy preterm infants Skin blanching from the cream is also common. For most routine infant blood draws, sucrose and breastfeeding are both more effective and safer.
Does Warming the Heel Actually Help?
Warming the heel before a capillary blood sample is a time-honored practice. The idea is that heat dilates the tiny blood vessels, making blood flow faster and reducing the need to squeeze. Many hospital protocols still mandate it. But recent evidence suggests the benefit may be smaller than assumed, or even nonexistent.
A randomized controlled trial comparing three different warming methods found that although the methods produced measurably different skin temperatures, there was no difference in blood flow velocity, hemolysis, or infant comfort scores between the groups.20PubMed Central. Warming Prior to Heel Stick Blood Sample Quality and Infant Comfort—A Randomized Controlled Trial A study specifically in very low birth weight newborns went further, comparing heel sticks with and without prior warming and finding no clinically relevant differences in any outcome. The researchers concluded that preheating the heel may be an unnecessary step.21PubMed. Heel Warming in Very-Low-Birth-Weight Newborns for Capillary Blood Sampling This does not mean warming is harmful; it is just that the time spent preparing a warm compress may not be buying you anything except a short delay before the inevitable stick.
Capillary vs. Venous Samples and Why the Difference Matters
A persistent source of confusion in neonatal medicine is that blood from a heel stick and blood from a vein do not give identical lab results. A study comparing capillary and venous complete blood counts in newborns found that capillary samples consistently showed higher hemoglobin, hematocrit, red blood cell counts, and white blood cell counts, while venous samples had higher platelet counts.22PubMed. Significant differences between capillary and venous complete blood counts in the neonatal period The practical implication is that a hemoglobin value from a heel stick cannot be directly compared with a reference range derived from venous blood, and vice versa. If a borderline result is obtained by one method, clinicians often repeat it using the other to confirm.
Capillary sampling also carries a higher burden of pre-analytical errors. An observational study of nearly a thousand pediatric blood samples found that about 20% of capillary samples had some kind of pre-analytical error, compared with roughly 9% of venous samples, making capillary collection about three times as error-prone after adjusting for other factors.23PubMed Central. Capillary blood sampling increases the risk of preanalytical errors in pediatric hospital care: Observational clinical study The most common problems include hemolysis, clotting in the tube, and insufficient volume. This is one reason venipuncture tends to be preferred once babies are large enough for the veins to be practical.
How Much Blood Loss Is Too Much
Healthy full-term babies can handle the small volumes taken for routine screening without any issue. The story is very different for extremely premature infants who spend weeks or months in the NICU with frequent lab monitoring. These babies have tiny total blood volumes to begin with, and the cumulative loss from repeated draws adds up.
A study tracking iatrogenic blood loss in extreme preterm infants found that the median cumulative loss was about 24 milliliters per kilogram of body weight per patient, which works out to roughly 29% of total blood volume. The most premature babies fared worst, losing about 30 milliliters per kilogram at 24 weeks’ gestation compared with about 16 milliliters per kilogram at 27 weeks.24PubMed. Iatrogenic blood loss in extreme preterm infants due to frequent laboratory tests and procedures This is a major driver of anemia in the NICU and a frequent reason these infants need red blood cell transfusions. Efforts to reduce unnecessary lab draws, use micro-sample tubes, and develop point-of-care testing that requires only a few drops are all aimed at this problem. Researchers have even developed rule-based calculator systems to help clinicians estimate exactly how much blood a given set of ordered tests will require from a specific infant, flagging when the total draw volume approaches a risky percentage of that baby’s blood supply.25Archives of Advanced Engineering Science. Development of an Expert System Calculator for Pediatric Blood Draw: A Conceptual Study
Rare but Real Complications of Heel Sticks
For the vast majority of infants, a heel stick leaves nothing behind except a tiny mark that fades in a day or two. The blood spot procedure can cause pain, local nerve irritation, minor bleeding, and a small risk of infection or scarring.26British Journal of Nursing. A safety lancet for neonatal blood spot tests: a design that facilitates pain-free, atraumatic samples In extremely rare cases, the puncture can introduce bacteria into the calcaneus, leading to osteomyelitis, a bone infection. A systematic review of heel-puncture-related calcaneal osteomyelitis in newborns found that while most cases resolved with antibiotics, some children followed for years afterward developed calcaneal deformity or flatfoot.27PubMed Central. Systematic Review of Heel Puncture-Related Osteomyelitis of the Calcaneal in Newborn Infants Proper site selection, staying on the medial and lateral aspects of the heel and avoiding the posterior curve, is the primary defense against this, since it keeps the blade far from the bone.
Parents seeing their newborn’s heel pricked for the first time often find it distressing, but the evidence overwhelmingly supports these routine screenings. The conditions caught by newborn blood spot testing, things like phenylketonuria, congenital hypothyroidism, and sickle cell disease, can cause irreversible harm if missed. A brief heel stick is a very small price for catching them early. If you want to help your baby through it, ask whether you can breastfeed during the draw or provide skin-to-skin contact. The science backs you up: your presence and touch are among the most effective pain relievers available for a procedure this brief.