Chapter 10. Neonatal blood tests
Introduction
There are a number of reasons why a midwife might need to perform blood tests on a newborn baby, and these include: newborn screening tests; serum bilirubin tests; and blood glucose monitoring. All of these tests involve a ‘heel prick’ to draw a small amount of blood from the baby’s heel. This procedure often raises anxiety in the parents and the student midwife in particular. Learning to undertake this test with compassion and dexterity is paramount to minimize the dread it has the potential to evoke.
Consider the following scenario and the questions which follow it in relation to newborn screening tests:
Megan, student midwife, felt nervous as she cuddled the week-old baby. Her face was flushed as she turned to the new mother and mumbled, ‘You can leave the room while I do this if you want.’ She wished everyone would go, including the midwife. Last time she had tried to do the blood spot test, the midwife had to take over. She really did not want to fail again.
What do you need to know in order to interpret this situation? Reflecting on this scenario you may have asked yourself:
■ Why would the woman wish to leave the room?
■ Why was the student so anxious?
■ What was the test for?
■ How was it taken?
■ Why would the midwife have to take over?
■ What could the student do to increase her chances of success this time? 
Newborn screening tests
The detection of abnormal conditions in both the mother and baby is an important part of the role of the midwife, as is the ability to recognize when to take action following the discovery of any abnormality (NMC 2004). Screening has become a complex issue as more screening tests become available. The United Kingdom (UK) National Screening Committee defines screening as:
Screening is a public health service in which members of a defined population, who do not necessarily perceive they are at risk of, or are already affected by a disease or its complications, are asked a question or offered a test, to identify those individuals who are more likely to be helped than harmed by further tests or treatment to reduce the risk of a disease or its complications.
(UKNSPC 2007)
Much of the examination carried out on babies during their first year of life is a form of screening, including the newborn examination carried out in the first 24–48 hours of life, and the weight and growth checks carried out by midwives and health visitors. While some tests focus on confirming normality, some tests are carried out specifically to identify certain diseases or conditions. The metabolic screening or dry spot test (also known as the Guthrie test) is one form of screening which tests for certain inherited diseases. The UK Newborn Screening Centre has been set up to monitor this screening programme. Each year approximately 250 babies with phenylketonuria (PKU) or congenital hypothyroidism (CHT) are identified through screening, allowing effective treatments to be started before irreversible neurological damage has occurred, preventing lifelong disability (UKNSPC 2007).
Current metabolic screening (dry spot; blood spot)
Based on the Guthrie test which was developed by Dr Guthrie in the early 1960s, its primary purpose was to monitor blood phenylalanine levels in patients with PKU. It has been used in the UK to screen newborn babies for PKU since 1969 (UKNSPC 2007). Since then a number of other screening tests have been added to the screening programme, including congenital hypothyroidism and a range of other conditions. A spot of blood from a heel prick is collected on a piece of blotting paper and allowed to dry. The Guthrie card enables four separate spots of blood to be collected and hence a range of conditions can be identified. Discs of this paper are then punched out and subjected to laboratory testing. This test is usually performed on or around the sixth postnatal day.
The conditions that are screened for may vary between health authorities. Cystic fibrosis screening is currently being implemented across England but is still not available in all areas (UKNSPC 2007).
Some health authorities undertake anonymous HIV prevalence surveillance using the Guthrie card. The midwife must keep abreast of such developments in order to provide parents with accurate information about the screening of their baby (NMC 2004). It is essential that the practitioner develops an understanding of the conditions that the sample will be tested for so that she can provide parents with accurate information in a clear and concise manner.
Phenylketonuria (PKU)
This is an autosomal recessive condition affecting approximately 1 in 10000 newborn babies (Hull & Johnston 1993). The enzyme phenylalanine hydrolase is missing from the liver and thus phenylalanine cannot be converted to tyrosine. Phenylketones build up in the blood, accumulate in the brain and result in permanent brain damage (Burroughs & Leifer 2001). However, if detected early, damage can be prevented by the strict application of a phenylalanine-restricted diet.
Capillary blood is collected from the neonate via the Guthrie test. The test involves placing the punched spot of blood-soaked filter paper onto a plate of agar jelly with a bacterium that requires phenyalanine in order to grow. A positive test is therefore one in which the bacteria has grown. Bacterial growth may be inhibited if an alcohol swab is used: they should therefore not be used for Guthrie tests.
The practitioner taking the test must ensure that she documents when the baby had its first milk feed, as the baby must have ingested milk protein for at least 48 hours for a positive result to be obtained (Johnson & Taylor 2006).
If the baby is receiving antibiotics, either directly or via breast milk, they can inhibit growth of the bacteria leading to a false negative result. Johnson & Taylor (2006) recommend taking the test 48 hours after the antibiotic course has been completed.
Congenital hypothyroidism (CHT)
Babies with congenital hypothyroidism do not produce thyroid hormones properly, which can affect the development of the baby’s organs, in particular the brain (UKNSPC 2007). If the condition is identified early the baby can be treated and can lead a healthy life (UKNSPC 2007).
Cystic fibrosis (CF)
CF is caused by a genetic defect occurring on the CFTR gene. Many parts of the body are affected including the pancreas and its secretions leading to malabsorption, malnutrition and vitamin E deficiency, and the lungs, resulting in frequent chest infections and lung damage. Cystic fibrosis also causes infertility in males and a shortened life expectancy.
Sickle cell disease (SCD)
SCD is an inherited disorder of the red blood cells which leads to haemolytic anaemia with the blood cells changing into a sickle shape. The sickle cells cause thrombosis and obstruction in small vessels, leading to tissue ischaemia and necrosis. The mutated allele is recessive, meaning it must be inherited from each parent for the individual to have the disease. Screening for sickle cell disease aims to identify affected infants, as early diagnosis allows prophylaxis with penicillin and vaccines, and parent training to identify children with complications and to present early for treatment which has been found to reduce complications and deaths in young infants (NHS Sickle Cell and Thalassaemia Programme 2007).
Medium chain acyl co-A dehydrogenase deficiency (MCADD)
MCADD is a rare hereditary disease that results from the lack of an enzyme required to convert fat to energy. The disease complications usually occur when the baby has long periods between meals, causing the body to use its fat reserves for energy. When this action is blocked by the lack of the necessary enzyme, serious life threatening symptoms and even death can occur. With early detection and monitoring, children diagnosed with MCADD can lead normal lives. All newborns will be screened for MCADD by March 2009 (UKNSPC 2007).
Other neonatal blood tests
Serum bilirubin test (SBR)
In their first few days of life, all babies begin to destroy fetal red blood cells, replacing them with new red blood cells. The rapid destruction of red blood cells and subsequent release of fetal haemoglobin into the bloodstream results in the production of bilirubin, a waste product produced by the liver. Bilirubin is excreted in bile, and eliminated in the faeces. Immediately after birth, more bilirubin is produced than the infant’s immature liver can handle, and the excess remains circulating in the blood. This can lead to neonatal jaundice, which if severe can lead to complications.
The level of bilirubin in the newborn’s blood can be measured via the SBR test. The bilirubin test will determine if hyperbilirubinaemia is present and allows the neonatal team to determine if the condition is relatively normal (benign) or possibly related to liver function problems or other conditions.
Blood glucose test (BM)
Glucose is the main energy source for the newborn baby and the brain depends almost exclusively on this energy, but glucose regulation mechanisms are sluggish at birth. This leaves the newborn at risk of hypoglycaemia if metabolic demands are increased or in the presence of other conditions. Severe or prolonged hypoglycaemia can lead to long-term brain damage. Blood glucose can be measured using heel prick blood on a specially designed reagent strip which is then inserted into a glucometer for reading.
The procedure for obtaining a heel prick specimen of blood
1. The midwife discusses the procedure with the woman enabling her to understand its relevance to her care and give informed consent
The client should have been given information regarding the screening test prior to the date set for it to be carried out. For the SBR and BM, the client should be fully aware of the nature and reasons for the test and what to expect from you and the other members of the midwifery care team. It is your responsibility to check that the client has had and understood this information, and at the same time you should check the plan of care for any other relevant information. The need to discuss the relative benefits of newborn screening should not be overlooked in your haste to complete the procedure. Similarly, parents need to know what the subsequent actions might be following the BM or SBR test.
Carrying out the ‘heel prick’ involves balancing the need to collect sufficient blood, with the potential for discomfort for the baby and unease for the parents. The parents should be prepared for what you are going to do and offered the option to leave the room if they feel they will be distressed. However, it may be useful to perform the procedure with the parent holding the infant.
2. The procedure is carried out at the appropriate time according to the woman’s plan of care
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