Screening tests in Newborns

Screening tests in Newborns

[mme_highlight] The goal of screening newborns is to detect diseases early, either because the tested diseases are life-threatening or because they can bring serious complications. The conditions which can be detected include inborn errors of metabolism, endocrine disorders, hemoglobinopathies, immunodeficiency, cystic fibrosis, and critical congenital heart defects.
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The goal of screening newborns is to detect diseases early, before symptoms appear, either because the tested diseases are life-threatening or because they can bring serious complications for health if the diagnosis is done late. In addition to the early detection, the screening has the aim of providing referral and treatment of babies thought to be affected by such conditions.
Newborn screening began in the 1960s when the scientist Robert Guthrie developed the blood spot test, which initially only detected Phenylketonuria (PKU), a metabolic disorder.  Nowadays, the test can detect more than 60 disorders, depending of the panel of diseases defined by every country.  The conditions which can be detected include inborn errors of metabolism, endocrine disorders, hemoglobinopathies, immunodeficiency, cystic fibrosis, and critical congenital heart defects.

My baby looks healthy…why will she/he be screened?

Yes, newborn screening is part of Public Health programs developed by each country and all babies undergo screening even if they look perfectly healthy, because some diseases do not cause symptoms or show any manifestation soon after birth but can become serious later. Statistics show that newborn screening detects treatable conditions in 1 in each 300 babies per year.

How is the blood spot test done?

This test is generally performed by a nurse between the 3rd and 6th days after birth. A lancet is applied on the lateral borders of the baby’s heel. It is necessary to wait till a drop of blood is formed, which will then fill in each circle on the screening paper sheet. This sheet is then sent to the laboratory and parents have to wait for the test results. In most countries, parents know the results 4 weeks after the test, if they are normal. In case of alterations in the test, parents are usually notified sooner than this.

What does it mean if the test results are normal?

If the results are negative it means that none of the conditions included in the screening was detected. The test is highly specific (99 to 100%), which boosts the security of a negative result as truly negative.

What does it mean if the test results are abnormal?

A positive or out-of-range result does not mean your baby has got a disease. It means that he/she will need further testing. The apparent sensitivity for most of diseases screened are 100% and specificity levels are all above 99%. However, there is a lack of evidence regarding the false negatives and false positives for individual diagnosable disorders included in this screening and the positive predictive values range from 0.5% to 6.0%. Consequently, on average, there are more than 50 false-positive results for every true-positive result identified through newborn screening in the United States.

What diseases can be diagnosed with this screening?

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Screening Outcomes (United States statistical data)

  • Detection rate: 1:4000 live births
  • 5 most frequently diagnosed diseases:
  • hearing loss
  • primary congenital hypothyroidism
  • cystic fibrosis
  • sickle cell disease
  • medium-chain acyl-CoA dehydrogenase deficiency

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Primary congenital hypothyroidism

The diagnosis of this condition of the thyroid gland is based on the levels of TSH (a hormone). If diagnosed lately, primary congenital hypothyroidism can lead to serious mental retardation and non-reversible neurological problems. The prognosis depends on the time passed before replacement therapeutic is initiated.

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Incidence Rates of Congenital Hypothyroidism (United States statistical data)

  • 1991: 2.89 cases per 10000 births
  • 1996: 3.67 cases per 10000 births
  • 2000: 3.86 cases per 10000 births

Incidence – number of new cases within a specified time period in a population.
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Hemoglobinopathies including sickle cell disease

Sickle cell disease is a common hereditary blood disorder in which red blood cells present an odd shape caused by a mutation in the hemoglobin gene. The life expectancy is shortened. Finding sickle cell disease early through newborn screening helps to prevent deaths and other complications that can appear.

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Sickle Cell disease-related mortality  0 to 3 years age group (United States statistical data 1983-2002)

  • 1983: Death rate 2.42 per 100.000 black children
  • 2002: Death rate 0.78 per 100.000 black children

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Cystic fibrosis

This is an inherited disorder of the mucus glands. Mucus is a substance that covers lungs, digestive system, reproductive system as well as other organs, protecting them. In cystic fibrosis, the body produces too much mucus, which is abnormally thick and sticky, which. Without an early diagnosis and treatment, this condition can cause serious complications and even early death.

Hearing loss

1 to 3 in each 1000 apparently healthy newborns have hearing loss, 20 to 40 per 1000 if risk newborns. This should be identified before 3 months and intervention should start not after 6 months, since a normal hearing function is required to language development.

Phenylketonuria

This is an inherited disease characterized by a deficiency in the enzyme phenylalanine hydroxilase, whose function is to metabolize phenylalanine (an amino acid). The accumulation of this amino acid becomes toxic in the body. Treatment consists in a hypoproteic diet, with restriction of phenylalanine.

Summary and Recommendations

  • Newborn screening, known as the blood spot test, tests a long list of diseases which may be life threatening or cause severe complications if not diagnosed and treated early.
  • All newborns should be screened with this test, even if they look healthy, because many diseases do not show signs after birth and can only become apparent when it is too late.
  • The blood spot screening test results are very reliable.
  • Examples of diseases that can be diagnosed with this screening are: hearing loss, primary congenital hypothyroidism, cystic fibrosis, sickle cell disease, phenylketonuria.

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References

  • Centers for Disease Control and Prevention (CDC). CDC Grand Rounds:Newborn Screening and improved outcomes. MMWR Morb Mortal Wkly Rep 2012; 61:390.
  • Kwon C, Farrell PM. The magnitude and challenge of false-positive newborn screening test results. Arch Pediatr Adolesc Med. 2000 Jul;154(7):714-8.
    1. http://www.cdc.gov/ncbddd/pediatricgenetics/newborn_screening.html (accessed 29.10.2013).
    2. http://www.cdc.gov/ncbddd/pediatricgenetics/data.html (accessed 29.10.2013).

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