For decades taking a blood sample by pricking a newborn's heel to test for phenylketonuria (PKU), an inherited metabolic disorder, has been standard practice in hospitals. But a new study suggests that the practice is painful and that taking blood from the back of a baby's hand hurts less.
Researchers at the Karolinska Hospital in Stockholm divided 120 healthy, full-term newborns into three groups. The first group of 50 babies underwent PKU testing by having blood taken from a vein on the back of the hand using a needle (venipuncture). The second group had blood from the heel taken using a small lancet; in the third group the heel was punctured with a large lancet.
To assess pain, the team of researchers led by Dr. Bjorn A. Larsson recorded the intensity and duration of crying as well as "total screaming time" and videotaped the infants' expressions. They then scored the facial expressions using a widely accepted coding system that measures infants' pain. The team also administered sham heel lancing on a control group of 11 babies.
In their study published in the May issue of Pediatrics, the team found that crying and scores on the expression test showed that the venipuncture group had significantly less pain than did those whose heels were lanced. Those whose heels were lanced using the large instrument expressed the greatest distress.
In addition, only one attempt to draw blood was necessary for 86% of the venipuncture group; success on the heel stick group was lower: 19% in the small lancet group and 40% in the large lancet group.
The findings, the team wrote, have broader implications. Sampling by heel prick is a common procedure performed on newborns and in some cases is performed repeatedly.
Repetitive painful procedures can lead to hypersensitivity reactions that can trigger a chronic pain response.