Neonatal screening for congenital hypothyroidism in Mexico: experience, obstacles, and strategies

A literature review on the redundancy of additional thyroid function tests in neonates of mothers with hypothyroidism

AIM

Newborn thyroid screening tests are carried out during the first days after birth in many parts of the world. The aim of this review was to assess whether additional thyroid function tests of neonates born to mothers with hypothyroidism are necessary to diagnose newborns with congenital hypothyroidism (CH) missed by the usual screening test.

METHODS

A search in PubMed and Google Scholar databases was conducted for pertinent studies, using relevant keywords. All studies that were published in any language from 1 January 2000 to 30 June 2023 were included. Observational cohort studies were included in the analysis, while case reports and studies not referring to neonates were excluded.

RESULTS

Thirteen studies were identified comprising more than 4400 infants with CH. Studies with the larger study populations recommended against additional testing in healthy infants of hypothyroid mothers. Similar were the results of some smaller retrospective studies. Few studies identified in total 16 infants with CH that were missed on neonatal screening without, though, a definite causative link between the mother's and the infant's thyroid dysfunction.

CONCLUSION

Based on available data, additional thyroid function tests seem redundant in identifying undiagnosed cases of CH. Larger studies are needed to reach a definite conclusion.

Newborn Screening Guidelines for Congenital Hypothyroidism in India: Recommendations of the Indian Society for Pediatric and Adolescent Endocrinology (ISPAE) - Part I: Screening and Confirmation of Diagnosis

The Indian Society for Pediatric and Adolescent Endocrinology has formulated locally relevant Clinical Practice Guidelines for newborn screening, diagnosis and management of primary congenital hypothyroidism (CH).

RECOMMENDATIONS

Screening should be done for every newborn using cord blood, or postnatal blood, ideally at 48 to 72 h of age. On this screen sample, neonates with TSH > 20 mIU/L serum units (or >34 mIU/L for samples taken between 24 to 48 h of age) should be recalled for confirmation. For screen TSH > 40 mIU/L, immediate confirmatory venous T4/FT4 and TSH, and for milder elevation of screen TSH, a second screening TSH at 7 to 10 d of age, should be taken. Preterm and low birth weight infants should undergo screening at 48-72 h postnatal age. Sick babies should be screened at least by 7 d of age. Venous confirmatory TSH >20 mIU/L before age 2 wk and >10 mIU/L after age 2 wk, with low T4 (<10 μg/dL) or FT4 (<1.17 ng/dL) indicate primary CH and treatment initiation. Imaging is recommended by radionuclide scintigraphy and ultrasonography after CH is biochemically confirmed but treatment should not be delayed till scans are performed. Levothyroxine is commenced at 10 to 15 μg/kg in the neonatal period. Serum T4/FT4 is measured at 2 wk and TSH and T4/FT4 at 1 mo, then 2 monthly till 6 mo, 3 monthly from 6 mo-3 y and every 3-6 mo thereafter. Babies with the possibility of transient congenital hypothyroidism should be re-evaluated at age 3 y, to assess the need for lifelong therapy.

Utilization of blood spot testing for metabolic-genetic disorders in Honduras: is it time for newborn screening?

Honduran infant mortality (20/1000) has fallen below the Latin American newborn screening target rate (<30/1000). The authors report 2 Honduran maple syrup urine disease cases and a newborn screening pilot study. The first infant, diagnosed by plasma/urine testing in the U.S., prompted this study. Although marked clinical/radiological improvement occurred after treatment, moderate neurodevelopmental delays persist at 5 years. This 1-month, prospective study used blood spot specimens from hospitalized term Honduran neonates shipped overnight to South Carolina for routine newborn screening with electronic result submission to Honduras for follow-up. Of 88 consecutive neonates (mean age: 4.2 days, standard deviation: 4.2 days) tested, 24 (0.6%) of 3837 completed tests were positive. Another infant with maple syrup urine disease, diagnosed after study completion by blood spot testing, later died. The study findings indicate that collaborative blood spot testing aids in the diagnosis of Honduran metabolic-genetic disease. Newborn screening is now needed to diagnose and treat these diseases before morbidity/mortality develops.

Neonatal TSH screening: is it a sensitive and reliable tool for monitoring iodine status in populations?

Iodine deficiency is the most common cause of preventable brain damage in the newborn. The indicators for assessing iodine nutritional status include urinary iodine excretion, thyroid size, thyroid stimulating hormone (TSH) and thyroglobulin (Tg) concentrations in the blood. Neonatal TSH concentration is increased when the supply of thyroid hormone and iodine from the maternal circulation to the foetus has been compromised. The World Health Organization (WHO) has suggested that when a sensitive assay is used on samples collected 3-4 days after birth, a <3% frequency of TSH concentrations >5 mIUl(-1) indicates iodine sufficiency in a population. However, many studies have attempted to apply the frequency of neonatal TSH values >5 mIUl(-1) in determining population iodine status and monitoring intervention programmes, and although some have proven to be successful, most have provided conflicting or uncertain data. This is due to the many technical issues that remain unresolved on the use of neonatal TSH screening for monitoring iodine status, making it doubtful as a sensitive and reliable quantitative tool. More research is required to resolve these issues. In the interim, WHO should consider withdrawing its current guidelines for neonatal TSH screening for monitoring iodine deficiency in populations.

Prevalence of early neurodevelopmental disabilities in Mexico: a systematic review

OBJECTIVE: Early neurodevelopment disabilities (END) such as cerebral palsy (CP), deafness, blindness, epilepsy, and mental retardation (MR) are very important public health concerns. Although no strong data on END can be obtained in Mexico, the few papers concerning END epidemiology deserve systematic and critical review. Thus, this was the objective of the present paper. METHOD: We performed a systematic review of papers published reporting on the prevalence of END in Mexico. We performed a search in several medical data bases such as PubMed, Artemisa, ImBioMed, and LiLaCS. Each paper was downloaded, read and discussed. We only selected papers published between 1999 and 2008. RESULTS: No data on CP and epilepsy prevalence in infants have been found. Data on deafness prevalence report hearing loss in 0.65/1,000 healthy newborns, and in 2.6/100 in high-risk very premature infants. With regard to blindness, prevalence of retinopathy of premature infants in any stage was reported at ca 10.61 and 22.2/100 in high-risk premature infants. Congenital hypothyroidism (CH) prevalence in infants was found in 4.2/10,000 live newborns after a national universal screening survey. CONCLUSION: No universal data regarding the prevalence of END in Mexico have been investigated, with the exception of CH. Mexico needs more research to determine epidemiologic data focused on designing actions to prevent, treat, and rehabilitate END.

Newborn screening in Latin America at the beginning of the 21st century

Newborn screening (NBS) in Latin America took its first steps in the mid-1970s. Nevertheless, many years elapsed before it achieved its integration within the public health care system and its systematic and continuous implementation under a programme structure. Latin American countries can be characterized not only by their great geographic, demographic, ethnic, economic and health system diversity, but also by their heterogeneity in NBS activities, which gives rise to variation in degree of organization: countries with optimal fulfilment (Cuba, Costa Rica, Chile, Uruguay); others rapidly expanding their coverage (Brazil, Mexico, Argentina); some others in a recent implementation phase (Colombia, Paraguay, Venezuela, Nicaragua, Peru); others with minimal, isolated and non-organized activities (Guatemala, Dominican Republic, Bolivia, Panama, Ecuador); and finally others without any NBS activities at all (El Salvador, Honduras, Haiti). Despite this disparity, a sustained and significant growth in NBS activities has become evident during the last decade, highlighted by implementation of new programmes, increase in coverage, expansion of NBS panels, increasing involvement of governmental and public health authorities, and integration of NBS teams through scientific societies and External Quality Assurance Schemes. Currently, congenital hypothyroidism (CH) is the most widely screened disease, followed by phenylketonuria, with organized NBS programmes for CH in 14 countries. Other diseases usually included in NBS programmes are screened in a lower rate. Every year, around 11.2 million infants are born in Latin America. During 2005, 49.3% of newborns were screened for CH, indicating that around 5.7 million newborns still did not have access to the benefits of NBS.

Neonatal TSH levels as an index of iodine sufficiency: differences related to time of screening sampling and methodology

INTRODUCTION

Current WHO guidelines consider that under adequate iodine intake <3% of newborns should have neonatal TSH levels of >5 mU/l blood when screening is performed in cord blood or at 3 days to 3 weeks of age.

OBJECTIVE

To estimate whether this absolute criterion when applied to newborns older than 48 h of age and native to Buenos Aires coincides with the traditional ones (goiter and urinary iodine in school-age children (SAC)), and if the evaluation varies with either the methodology used for TSH measurements and/or the time of specimen sampling.

POPULATION AND METHODS

TSH was measured by an immunofluorometric assay (IFMA) on filter paper blood spots of 186 cord blood samples, 112 babies <48 h of age and 1,500 newborns >48 h of age, and by immunoradiometric assay (IRMA) in 238 newborns. The WHO ICCIDD absolute criteria were applied to each population. Thyroid volume was assessed by direct palpation in 500 SAC, and in 100 of them urinary iodine levels were measured.

RESULTS

TSH levels were >5 mU/l blood in 11.3% of the cord blood samples and in 3.6% of the samples from babies <48 h of age, suggesting mild iodine deficiency. TSH was >5 mU/l in 2.7% of newborns >48 h of age tested by IFMA (iodine sufficient) and in 30% measured by IRMA (moderate iodine insufficiency). Median urinary iodine and goiter prevalence in SAC were 143 mug/l and 4.5%, respectively, as expected in an iodine-sufficient area. conclusion: The TSH levels in Buenos Aires conform with the WHO criterion that defines iodine sufficiency. Application of this criterion, however, to cord blood samples or samples from babies <48 h old and the use of different methodologies may lead to erroneous conclusions.

Thyroid stimulating hormone levels in cord blood are not influenced by non-thyroidal mothers' diseases

CONTEXT

Screening programs not only offer the opportunity to trace and treat almost all cases of congenital hypothyroidism but also mean large savings to the health system. However, carefully planned strategies are necessary to extend their benefits and reduce costs.

OBJECTIVE

To determine the possible influence of maternal diseases that affect maternal-fetal placenta dynamics on primary thyroid stimulating hormone (TSH) screening for congenital hypothyroidism.

DESIGN

Prospective non-randomized clinical trial with at least 3 months of follow-up.

SETTING

A public university referral center [CAISM/Hospital das Clínicas, Faculty of Medicine, University of Campinas, Campinas, SP].

PARTICIPANTS

415 neonates divided into 5 groups: eighty-three infants born from cardiac mothers; 98 from mothers that had toxemia; 54 of the mothers had diabetes mellitus; 40 were HIV positive and 140 had no diseases.

INTERVENTION

All newborns had cord blood samples collected on filter paper at birth.

MAIN MEASUREMENTS

TSH was measured from dried blood spots using a homemade immunofluorescence assay (sensitivity in dried blood spots = 0.1 mU/L).

RESULTS

There was no significant difference in the mean TSH levels among the 5 groups. Moreover, TSH levels were around 5 mU/L in 48% of the newborns, indicating that our region is severely deficient in iodine.

CONCLUSIONS

Our results indicate that primary TSH screening programs using cord blood are not affected by maternal diseases. We suggest that, besides its technical advantages over heel punctures with T4 primary approaches, neonatal screening using primary cord blood TSH may also be used as a monitoring tool for evaluation and control of iodine deficiency disorders (IDD).

Diagnosis of inborn errors of metabolism

Systematic detection of inborn errors of metabolism (IEM) has usually encountered difficulties in developing countries. We present our experience in a high-risk population in Mexico between 1973 and 1998 with particular reference to the last 10 years, during which time infrastructure and support were considerably improved. Only disorders of intermediary metabolism were sought. The total number of patients studied is not available, but in the last 10 years, patients numbered 5,186. Routine metabolic screening was performed on all patients, with additional tests according to the clinical picture and screening results. The referral criteria have increasingly diversified, one-third being neurological conditions. Of the referrals, 33.8% were from pediatricians (31.1% of whom were at critical medicine departments) and the remainder from specialists. The number of diagnosed patients has increased to 1 per 43.9 patients studied. Amino acid defects have been the most prevalent, the proportion of organic acid and carbohydrate disorders having increased in the last 10 years, associated with improved diagnostic facilities. The most frequently diagnosed diseases were PKU, type 1a glycogen storage, and maple syrup urine disease (MSUD), their frequency apparently varying among different regions of Mexico. Other results of our program include training of specialists and technicians, development of the Latin American Metabolic Information Network, a procedure to locally prepare a special food product low in phenylalanine for the treatment of PKU patients, and extension of approaches for these disorders to the investigation metabolic derangements of infant malnutrition. This work demonstrates that inherited metabolic diseases constitute a significant load in pediatric pathology and that their study can and should be pursued in developing nations.