Heel prick test

The neonatal metabolic screening programme, better known as the “heel prick”, is a blood test that is carried out on all newborns. This sample and a file with the baby's data are sent to the laboratory where more than 60 markers are analysed to screen for the 25 diseases included so far. When any of the markers studied is altered, this is communicated to the clinical reference unit which contacts the family to perform other studies to confirm or rule out the disease.

It can be used to detect 25 diseases in which rapid action can change the prognosis. The diseases included in the programme are:

• Congenital hypothyroidism.
• Cystic fibrosis.
• Phenylketonuria.
• 5 further amino acid metabolism disorders.
• 8 organic acid metabolism disorders.
• 6 fatty acid metabolism disorders.
• Sickle cell disease.
• Severe combined immunodeficiency.
• Biotinidase deficiency disorder.

Screening can also detect healthy children who have a genetic alteration related to a condition, but who will not develop the disease itself. They are known as carriers. Diseases that are not part of the programme may also be diagnosed. In this case, the same procedure is followed as for other diseases. 

The diseases included in the programme have a treatment that, when given early, can prevent or reduce the symptoms and injuries that would result without appropriate action. 

A superficial prick is made on the baby's heel. The puncture has to be made in the most lateral portion of the plantar surface of the heel. A few drops of blood are extracted and used to cover approved absorbent paper on both sides. This paper is sent to the laboratory for analysis. Along with taking the blood, data on the family and the newborn are collected on a form that will later be used to send the results obtained and contact the parents, if necessary. The ideal time to do this is 48 hours after birth, at the hospital where the baby was born. 

Performing the test only takes a few minutes, and the results will be received approximately three weeks later. In most cases the test results are normal. In the event that an abnormality is detected, medical professionals will contact the family.

Nursing staff prepare the material necessary for the test (sterile gauze, antiseptic, capillary, specific incision device or lancet, dummy and sucrose). The specific incision devices used for the heel prick test outline an arc where the puncture is made. Delicate incision produces less pain, less bruising, facilitates healing and provides the necessary quantity of blood, thus reducing the number of repetitions.  

The newborn's foot is placed below the height of the heart to increase venous flow.   

A gentle massage is given to warm the area and it is verified that the newborn is at a comfortable temperature.

Hygienic hand washing is performed prior to putting gloves on, and then the newborn's heel is pricked. A gauze soaked in 2% aqueous or alcoholic chlorhexidine is recommended to disinfect the pricked area and then it’s left to fully dry on exposure to the air.

The heel must be perfectly dry before performing the test, as any residue may alter the results. 

The surface on which the paper is left to dry must be clean, dry and at room temperature. Exposure to sunlight or heat sources should be avoided. Soaking the paper with the blood must be done with the necessary precautions to ensure that the practitioner's skin does not come into contact with the filter paper circles, as this could alter the analytical results. Therefore, using gloves is recommended.  

This test is contraindicated in newborns where both heels are oedematous, injured or infected. In certain circumstances, the heel cannot be accessed for sampling. When heel prick testing is contraindicated or not possible due to local heel problems, venous blood sampling is recommended.  

Newborns admitted to the ICU can be assessed for the risk/benefit ratio of carrying out the heel test compared to taking an arterial/venous blood sample if they have an umbilical catheter. A venous puncture can be used to perform another analysis.  

In newborns who require a blood transfusion, the test should be performed prior to transfusion whenever possible, even within the first 48 hours of the baby’s life. The test should be repeated where appropriate, according to the type of transfusion. 

The test is performed by nursing staff at the health centre where the newborn was born.  

Prevention and treatment of pain must be considered an essential right for newborns. Some studies suggest that the presence of the mother (holding the child with skin-to-skin contact or breastfeeding during the process) can mean that the infant shows less distress. 

If the parents are not present at the time of the procedure, sucking a dummy can reduce pain scale scores. The maximum effect is achieved when breast milk or sucrose administration is used in conjunction with suckling and restraint (keeping the newborn in a flexed position with the limbs close to the torso, towards the midline). Newborns who are held like this during the procedure recover their basal heart rate more quickly, and express less pain. 

Possible sequelae for the newborn include residual pain and a small bruise around the puncture site, which disappears after a few days.