|Year : 2014 | Volume
| Issue : 1 | Page : 59-63
Expanded newborn screening: Guiding principles, concerns and relevance
Seema Pavaman Sindgikar, Rathika Damodar Shenoy
Department of Pediatrics, K. S. Hegde Medical Academy, Derlakatte, Mangalore, Karnataka, India
|Date of Web Publication||15-Mar-2014|
Rathika Damodar Shenoy
Department of Pediatrics, K. S. Hegde Medical Academy, NITTE University, Derlakatte, Mangalore - 575 018, Karnataka
Source of Support: None, Conflict of Interest: None
Since its introduction in 1960s, universal newborn screening (NBS) using the heel-prick dried blood spot samples has become an integral part of public health system in developed countries expanded to pre-symptomatic detection of specific inherited metabolic, endocrine and hematologic disorders. In our country, NBS may become relevant with epidemiological shift and increasing access to technology. Current recommendations include a phased introduction of screening for congenital hypothyroidism, congenital adrenal hyperplasia and glucose 6-phosphate dehydrogenase deficiency. In this review, the guiding principles of NBS, some of the individual disorders, the concerns and relevance to our country are discussed. Establishing a pre- and post-screening care and education are of utmost priority before NBS is adapted into health care system.
Keywords: Congenital hypothyroidism, dried blood spot, Guthrie card, phenylketonuria, tandem mass spectrometry
|How to cite this article:|
Sindgikar SP, Shenoy RD. Expanded newborn screening: Guiding principles, concerns and relevance. Muller J Med Sci Res 2014;5:59-63
|How to cite this URL:|
Sindgikar SP, Shenoy RD. Expanded newborn screening: Guiding principles, concerns and relevance. Muller J Med Sci Res [serial online] 2014 [cited 2019 Jul 20];5:59-63. Available from: http://www.mjmsr.net/text.asp?2014/5/1/59/128951
| Introduction|| |
Universal newborn screening (NBS) using heel-prick dried blood spot (DBS) samples has become an integral part of public health system in developed countries. It aims at pre-symptomatic detection of specific inherited metabolic, endocrine and hematologic disorders in the newborn period to advocate timely interventions that prevent mortality and long-term morbidity. Such disorders may not be detected otherwise before the affected infant presents with devastating neuro-developmental sequelae. The specific management thus started would help these neonates to develop normally. The prototype disorder identified by NBS is phenylketonuria (PKU), an inborn error of metabolism (IEM) wherein elevated blood phenylalanine levels causes mental retardation and irreversible neurologic damage. , Mandatory universal NBS was first introduced for PKU in Massachusetts, United States (US) in 1963.  Over the last five decades since then, with technological advances especially tandem mass spectrometry (MS/MS) and immunoassays, the NBS is "expanded" to encompass several disorders. In this review, the guiding principles of NBS, some of the individual disorders, the concerns and relevance to our country are discussed.
| History|| |
Discovered in 1934, identifying asymptomatic infants with PKU became a challenging proposition. In 1963, Robert Guthrie, a microbiologist with an affected niece innovated a card with filter paper to spot few drops of blood obtained from heel prick within two to three days of birth to screen asymptomatic newborns.  The DBS was assessed for elevated levels of phenylalanine using a microbiological inhibition assay. Guthrie's original work helped in establishing the NBS world-wide.  Followed by PKU many more metabolic disorders especially amino acidurias were included under NBS. A decade later in 1978 with the availability of immunoassays for thyroxine (T4) and thyroid stimulating hormone (TSH) congenital hypothyroidism (CH) was included in NBS panel. With the introduction of MS/MS in 2000, multiplex testing for several IEMs using filter paper DBS became possible and the NBS was expanded. Since 2006, in US about 29 conditions have been mandated for universal NBS as a public health program [Table 1] and these constitute the core panel.  An additional 25 conditions that are identified by the same technology, but lack treatment are secondary targets in NBS panel. There is no uniformity in the disorders screened and the core conditions screened is determined by the prevalence of the disorder in that population. ,, In US and Australia while it is 29 disorders in United Kingdom (UK) only six disorders are recommended for NBS. Urine based NBS is adapted in Quebec province of Canada where it is screened on Day 21 of life for 25 disorders of IEM by multiplex thin layer chromatography.  Thus screening programs throughout the world are very heterogeneous and most of them use DBS.
|Table 1: Core panel in newborn screening as mandated in US, the primary biomarker and screening strategy|
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NBS as Public Health Program: Guiding Principles and Concerns
Wilson and Jungner in 1968 put forth criteria for inclusion of a disorder under population screening which was reviewed by Anderman et al., in 2008. , For a disorder to be included in population screening it should be of sufficient public health importance; there should be adequate knowledge of natural history; a sensitive diagnostic test which is cost-effective should be available and more importantly treatment should be effective. Considering the number and diversity of conditions identified in NBS, as public health-based population screening program it needs to be comprehensive and coordinated consisting of education of parents and health providers, standardized screening techniques, interpretation of results, follow-up contact, confirmatory diagnosis by second tier testing, treatment initiation and program evaluation. NBS is not diagnostic and any presumptive positive result will require confirmation, preferably with an independent sample and test method. If a disorder which was screen negative is clinically considered later in life in a symptomatic infant or child the test should be repeated irrespective of NBS.
Umbilical cord blood sampling though sufficient for CH, is unsuitable for IEM as the abnormal metabolites are detectable only after initiation of feeds. Collection of blood onto an absorbent paper card (Whatman TM 903), often referred to as a "Guthrie card," is the commonest type of NBS sample.  A few drops of blood from a heel prick are collected onto the paper and allowed to dry in air for a few hours before sending to a central NBS laboratory. Most programs currently recommend sampling at 48-72 h of age. Prematurity, low birth weight (LBW), neonatal jaundice, parenteral nutrition, transfusions and type of feeds can all potentially influence NBS results and need to be taken into account when establishing cut-off values and interpreting results. Transport of samples is also important because some markers are relatively unstable and heat, humidity and delays in transport can cause degradation and potential false negatives.
The development and expansion of NBS has given rise to ethical concerns. ,, As a public health program critical issues of communication and parental consent or dissent are often overlooked. Others include psychological stress when screening is extended to disorders where treatment is only supportive or not necessary until later in life, detection of the carrier state, false positive and negative results. Screening may also influence parental reproductive decisions. Linkage of NBS information and results to public health vital statistics, storage and access to stored filter papers are other issues debated.
| Individual Disorders|| |
Although individually rare, the combined incidence of all the IEMs is estimated to be as high as 1 in every 4000 births.  The incidence of PKU is 1 in 14000. Phenylalanine levels >200 μmol/L and an increased phenylalanine/tyrosine ratio are considered screen positive. As multiple analytes are detected by MS/MS concerns of using this technology include the following: (i) Diagnosis of mild, benign or very rare disorders (ii) detection of disorders without effective treatment or established second tier testing (iii) common metabolites for several disorders (iv) requirements of tertiary centers and metabolic specialists for management.  All IEMs are not detected by MS/MS e.g., non ketotic hyperglycinemia which presents with neonatal encephalopathy. In contrast to US where up to 20 disorders constitute the core panel, in UK screening is restricted to PKU and medium chain acyl Co-A dehydrogenase deficiency, a fatty acid oxidation defect. ,
The most common cause of CH is thyroid dysgenesis: Aplasia, hypoplasia, or an ectopic gland. There is urgency to detect and treat CH as it the most common treatable cause of mental retardation. The worldwide incidence of CH ranges from 1:3000 to 1:4000 newborns. , However, data from Vellore, South India and Mumbai indicate prevalence of 1:1200 and 1: 2640 respectively suggesting that CH in India is higher. , Subsequent to the implementation of iodization program by Government of India, the incidence of CH has come down in the state of Uttar Pradesh.  NBS for CH include immunoassay measurement of TSH and/or T4. Single TSH measurement is simple with a relative low false positive rate. However it will not detect central hypothyroidism (1:500,000) and may be false negative in pre-terms and LBW due to hypothalamic immaturity. Estimation of T4 will miss those infants with minimally functioning or ectopic thyroid glands that seem normal at birth, then decline in function. Studies show no clear advantage of one over the other including simultaneous testing of T4 and TSH. Positive screen results require follow-up with formal thyroid function tests (TFT) and radionuclide scans.  Review of NBS CH data indicate that the true positive rate for CH was 3.9% of screen positive results i.e., only 1 in 26 newborns who are screen positive are true positive. It is important to note that TFT should be done irrespective of negative NBS if clinically suspected in later age. The American Academy of Pediatrics (AAP) provides an algorithm for interpretation and follow-up of NBS for CH. , In countries where NBS is not a public health program, CH alone may be screened by cord blood assay.
Congenital Adrenal Hyperplasia (CAH)
CAH is a group of disorders of the adrenal cortex with deficiencies in enzymes essential for steroidal hormone biosynthesis. The prevalence worldwide of CAH is reportedly 1:18000. , NBS focuses exclusively on the most common 21-hydroxylase deficiency which constitutes 90% of all cases of CAH. The disorder is amenable to replacement doses of gluco- and mineralocorticoid. The NBS for this disorder involves immunoassay of serum 17-OH progesterone. Females with classical CAH are clinically obvious at birth due to ambiguous genitalia; milder, non-classical forms usually have normal levels in the newborn period and are consequently not detected by NBS. Existing immunoassays cross-react with a number of steroids of foetal origin; preterm and LBW have high values. Around 200 unaffected newborns require clinical and laboratory follow-up for every true case of CAH.
Glucose-6-phosphate Dehydrogenase Deficiency (G6PD)
G6PD deficiency can lead to severe hyperbilirubinemia and acute bilirubin encephalopathy in the newborn period and acute hemolytic crisis in later age. Neonatal testing for G6PD deficiency is not yet routine in US and AAP recommends testing only in jaundiced newborns who are receiving phototherapy whose family history, ethnicity, or geographic origin suggest risk for the condition or when response to phototherapy is poor.  In contrast G6PD deficiency is most common genetic disorder in India and has been genetically mapped. , It has been extrapolated that the burden due to this disorder is likely to be nearly 390,000 births per year in our country.  The recommended screening test is the modified Formazan ring test while commercially enzyme-linked immunosorbent assay and enzyme assay are available. , A screen positive neonate will require definitive quantitative assay by spectrophotometry.
Universal Newborn Hearing Screening (UNHS)
When a criterion of >40 dB HL is used to diagnose moderate hearing loss, the world-wide prevalence of permanent, congenital bilateral hearing loss ranges from 1 in 900-1 in 2500 newborns. , One-to two-thirds of these have moderate bilateral hearing loss, whereas the remainder have severe or profound hearing loss. Study from Kochi, Kerala indicates incidence of hearing loss as 10.3/1000 in the high risk group and 0.98 per 1000 in the well-baby group.  Screening programs use a 2-stage approach (otoacoustic emission [OAE] repeated twice, OAE followed by auditory brainstem response [ABR], or ABR repeated twice). OAE evaluates the integrity of the cochlea and ABR evaluates the integrity of the peripheral auditory system and the auditory nerve pathways up to the brainstem. Concerns include missing "central" or delayed deafness due to cytomegalovirus intra-uterine infection and severe birth asphyxia; the gold standard test "visual reinforcement audiometry" cannot be performed reliably before 9 months of age and widely variable timing and type of intervention. The efficacy of UNHS to improve long-term language outcomes remains uncertain.
| NBS in India: The Relevance|| |
Currently, the disorders covered under expanded NBS have a minor contribution in reducing the overall infant mortality and morbidity. The cost of expanded screening in India is presently around Rs. 4000-5000 per sample and the sector is largely unorganised, commercial and limited to metropolitan cities. As a mandatory public health program "heel to heal" it is limited to the state of Goa since 2008 where it is integrated with the public health insurance scheme.  A total of 27578 newborns were screened between 2008 and 2011 and results suggest a higher incidence of these disorders in comparison to US data [Table 2]. However, the data may not be representative of the entire country and no long term data on management and follow-up of screen positive neonates are available. Results from Andhra Pradesh and the recently completed Indian Council of Medical Research multi-centric study (unpublished) also suggest a higher incidence of these disorders in our country. , Currently, recommended core screening for our country is a phased introduction of NBS for CH, CAH and G6PD. , This recommendation is based on the cost-effectiveness and prevention of lifelong morbidity and mortality. Expanded screening presently is largely limited to private health delivery system and introduction as a national program is neither feasible nor a priority. However, it may become relevant with epidemiologic transition, growth of upper middle class with smaller families, increase in commercial pressures and specialist professionals.  Concerns include second tier definitive testing, medical expertise, genetic services and special diets for those who are screen positive are not widely available.
|Table 2: Comparison of newborn screening results from Goa, India (2008-11) with US data,,|
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| Conclusion|| |
NBS is promising and challenging and grown beyond "PKU test." It has been very successful in the developed countries as a public health program. In our country, NBS may become relevant with the growing economy and increasing access to technology. Establishing a pre- and post-screening care and education are of utmost priority before NBS is adapted into health care system.
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[Table 1], [Table 2]