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Neonatal Thyroid Stimulating Hormone Screening in Latvia: a tool for Classification and Monitoring of Optimum Iodine Nutrition


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Neonatal Thyroid Stimulating Hormone Screening in Latvia:
A Tool for Classification and Monitoring of Optimum Iodine Nutrition

by
Ruzan H. Gyurjyan


Report extracted from a Masters of Public Health Thesis

Department of International Health

Rollins School of Public Health

Emory University

Atlanta, GA, U.S.A.

Abstract


BACKGROUND: Latvia, one of the Baltic States, is surrounded by nations that are iodine deficient. A nation-wide survey in 2000 among a sample of 587 schoolchildren yielded a median urinary iodine concentration of 59μg/L, indicative of mild deficiency. This report analyzes the national neonatal TSH screening data for 2000-2002 to obtain additional, independent evidence of the extent and severity of the problem in Latvia.

RESULTS: Upon cleaning the database for missing and/or inaccurate data, the results for 55,720 TSH blood spots remained for analysis, representing 93% of all registered births in Latvia during the observation period. For 2000-2002 combined, the prevalence elevated TSH (>5mIU/L) was 11.0% [95% C.I. 10.7 – 11.3] and this percentage fell with year of observation from 14.2% in 2000, to 10.4% in 2001 and 8.4% in 2002. A slight variation was apparent among administrative regions in the country, with the highest proportion of elevated TSH in Latgale region bordering Russia and Belarus, and the lowest in Kurzeme region along the Baltic Sea coast. A comparison by region of the neonatal TSH screening data of 2000 with the urinary iodine excretions among school children in the same year showed a positive correlation (r = 0.8; p<0.05) between the proportions of elevated neonatal TSH tests and low schoolchild urinary iodine levels.

CONCLUSION: Using WHO/UNICEF/ICCIDD criteria, these findings confirm that the population in Latvia is mildly to moderately iodine deficient, which exposes newborns to the risk of brain damage, mediated through inadequate thyroid hormone supply to the developing brain cells during fetal and early neonatal life. The existent national neonatal TSH screening offers a solid and comprehensive database for semi-annual reporting on national progress to ensure optimum iodine nutrition in the population in Latvia.


Neonatal Thyroid Stimulating Hormone Screening in Latvia:

A Tool for Classification and Monitoring of Population Iodine Nutrition


Introduction


Goiter and cretinism, the visible and long-standing manifestations of iodine deficiency, have long been considered as the most important consequences of deficient dietary iodine supply in a population. In 1983, the term iodine deficiency disorders (IDD) was coined to describe the various maladies of iodine deficiency in a population, most of which may also occur in an individual without goiter or cretinism. IDD encompass the broad range of consequences seen in an affected population group, principally provoked by deficient dietary iodine consumption and mediated through reduced thyroid hormone availability in the organs and tissues of the human body. Among these disorders, the damage of iodine deficiency in the developing brain during fetal and early neonatal life is of most concern for health, social and economic development.


The modern knowledge about the impact of low dietary iodine intake on human cognitive development and intellectual capacity was summarized during a landmark Symposium at the Franklin Institute, Philadelphia, U.S.A. (Stanbury, 1994). A meta-analysis covering more than 2,500 subjects from 3 continents in 21 studies found a mean IQ difference of 13.5% between iodine deficient and non-iodine deficient subject groups on neuromotor and cognitive function tests. In combination with findings accumulated from biomedical studies, the model has emerged that the sub-optimal IQ in an iodine deficient population is mediated through insufficient thyroid hormone availability, especially thyroxine, in the brain cells during the critical period of fetal and early neonatal brain growth (De Escobar, 2001). The damage caused by low thyroxine supply to the developing fetal brain due to insufficient dietary iodine intake by the pregnant woman impacts on the newborn’s intellectual performance, and thus on the ability of learning and earning later in life, and the economic performance of individuals, communities and nations (Maberly et al, 2003).

The severity of iodine deficiency in a population may be assessed on basis of biological measurements such as urinary iodine concentration (UIE), serum thyroid hormone levels, goiter prevalence and newborn blood spot thyroid stimulating hormone (TSH) levels (WHO/UNICEF/ICCIDD, 2001). An expert consultation of the World Health Organization (WHO), United Nations Children’s Fund (UNICEF) and International Council for Control of Iodine Deficiency Disorders (ICCIDD) recommended the use of at least two of these indicators, because any single parameter in isolation has its limitations and may bias the conclusion on a population’s iodine nutrition status.


In 2000, the Latvia Food Center organized a national survey among 587 schoolchildren in Latvia to assess the extent and severity of iodine deficiency and establish a baseline for future comparison in the progress to eliminate IDD in the population (Selga et al, 2000). Probability proportionate to size sampling was used: The survey included four clusters in the capital Riga and three to four clusters from each of the four regions in Latvia. Within each cluster, an average of 30 urine samples was analyzed for iodine concentration. The results indicated mild iodine deficiency in the nation – the median urinary iodine was 59μg/L. The frequency distribution showed adequate levels of iodine (>100μg/L) in only 23% of the children, while 19% had extremely low (<20μg/L) urinary iodine excretions. Differences among regions were also observed: The coastal towns Liepaya and Ventspils had slightly higher levels. The lowest levels (25.5% of children having <20μg/L) were detected in Zemgale and Latgale regions, bordering with Belarus and Russia.
The primary aim of neonatal TSH screening is to enable early detection of preventable severe mental retardation by swift diagnosis and treatment of congenital hypothyroidism. The data of national neonatal TSH screening can also serve as a basis to classify and monitor iodine deficiency, as well as the effect of efforts to alleviate iodine deficiency in a population (Nordenberg et al, 1993; Delange, 1999).

Recommended criteria of the 1999 WHO/UNICEF/ICCIDD expert consultation (WHO/UNICEF/ICCIDD, 2001) are: Neonatal TSH values above 5mIU/L in 3 - 19.9% of newborns in a population indicates mild iodine deficiency, 20 - 39.9% represents a moderate iodine deficiency level and at ≥40%, the population is classified as severely iodine deficient.

A study was conducted in 1998 to discern and classify the extent and severity of iodine deficiency in Estonia, the smallest of the Baltic States, using the national neonatal TSH screening data (Mikelsaar, 1999). The proportions of neonatal TSH >5mIU/L varied somewhat from 16% of newborns in the North, to 17% in the South and 21% in the Central regions. These results were in agreement with a median urinary iodine level of 65μg/L among school children reported in Estonia in 1995.
The objective of the present study was to assess and characterize the iodine nutrition status in Latvia on basis of the established national neonatal TSH screening. Data of the neonatal TSH screening over three consecutive years of 2000-2002 was used. In addition, we explored if the same data may be useful in discerning any differences among the various geographical regions of the country, and whether the national screening system may contribute to monitoring the progress in Latvia towards the goal of sustainable IDD elimination by 2005.

Neonatal TSH Screening in Latvia

National TSH screening among newborns in Latvia started in 1996 with the Order of the Minister of Health #324, dated 20 February 1995. The cut-off point for individual recall used in Latvia is 10mIU/L, i.e. when that level is surpassed in a newborn blood spot, additional biological tests are required to confirm or rule out congenital hypothyroidism. The information and blood samples obtained from maternities and hospitals throughout the country are sent to the Laboratory of the Genetic Center at the Republican Children Hospital “Gailezers” in Riga, where the samples are analyzed by enzyme immunoassay with fluorimetric detection for determination of human thyrotropin in dried blood spots on filter paper (Neonatal hTSH FEIA Plus by Labsystems, Finland).



Methodology


In Summer 2003, the Ministry of Health of Latvia requested access to the database of newborn TSH screening from the Genetic Center of the Gailezers Children Hospital for the three consecutive years of 2000-2002. The dataset was made available to the author in November 2003. Data analysis was conducted using SAS 8e software. Child-unique identifiers were removed and statistical analysis was performed on a password-protected PC. Data were validated prior to statistical calculations, and all negative data and TSH data with unidentifiable hospital codes were removed from the annual datasets.

Results

For the purpose of validation, the number of TSH tests in the database was compared against the total live births by year obtained from the State Statistical Department. As noted in Table 1, the coverage for all three years remained high. For 2000, the TSH coverage was 82%, for 2001 it reached 99% and the TSH data in 2002 were equivalent to 98% of the total number of live births registered in Latvia. The coverage in 2000 was lowest due to a relatively large number of negative observations in the original dataset, which were removed for the present analysis.
Table 1: Coverage of Neonatal TSH Screening for 2000-2002




Year

Total TSH tests in the present dataset

(a)

Valid TSH tests in the present dataset

(b)

Total live births in Latvia

(c)

Coverage of

present dataset

(b/c)

2000

19,610

16,832

20,236

83%

2001

19,314

19,313

19,593

99%

2002

19,600

19,575

19,973

98%


Figure 1: Neonatal TSH Distributions, Latvia 2000-2002


TSH Distributions

The neonatal TSH distributions for 2000, 2001 and 2002 are shown in Figure 1. Despite small year-to-year variations, the distributions have very similar shapes. A slight shift is seen toward lower TSH values with time, and thus each year a lower proportion of elevated newborn TSH values.



Trend analysis

Table 2 and Figure 2 describe the TSH results for Latvia by administrative region for the years 2000 through 2002. A steady decrease in prevalence is observed both nationally as well as in each region. The trend was statistically significant for all regions (p<0.0001).


Table 2: Prevalence of Elevated TSH in Newborns (>5mIU/L) in Latvia by Region


Region

Year 2000

Year 2001

Year 2002

Riga

13

10

6

Kurzeme

11

8

6

Vidzeme

18

8

9

Zemgale

12

9

8

Latgale

33

20

19

National

14.2

10.4

8.4



Figure 2: Elevated Neonatal TSH by Region, Latvia 2000 - 2002



Comparison of the 2000 TSH screening results with the 2000 UIE study

Following the recommendation by WHO/UNICEF/ICCIDD to use at least two indicators for the classification of iodine deficiency in a population, the findings of the UIE study among school children conducted in 2000 by the Latvia Food Center were compared with the present results of the TSH screening data among neonates during the same year. Figure 3 below is a plot of proportions of UI among schoolchildren below the sufficiency level of 100μg/L against the proportions of neonates with elevated blood TSH levels.



Figure 3: UIE test vs. TSH Screening Results by Regions of Latvia, 2000




Although iodine deficiency existed all over the country, some variation among regions was observed.

Latgale region, bordering with Russia and Belarus, showed the highest levels of deficiency by both indicators. The mildest deficiency was observed in Kurzeme region, located in Western Latvia around the Gulf of Riga and Baltic Sea. The other regions of the country showed intermediate results in both studies. The combination of studies indicates that mild-to-moderate deficiency exists all over Latvia’s territory.
The two sets of variables -the proportions of neonatal elevated TSH tests and low school-child UIE- are positively correlated (Pearson moment correlation coefficient r = 0.8; p<0.05). This means that the two variables, while obtained independently, increase or decrease simultaneously, which allows the inference that both biological indicators similarly identify the existence of iodine deficiency in the Latvia population.


The UIE study conducted in 2000 had a small sample size, and therefore, some regions or population strata, in particular the rural population in inland and coastal regions of Latvia may have been underrepresented. One of the findings of the UIE study that the inland areas are generally detecting higher levels of iodine deficiency compared to coastal was based on the analysis of data from the two coastal cities of Liepaya and Ventspils. The TSH screening analysis expanded the sample size to all newborns of the country and yielded the same conclusion, however. Thus, based on both indicators, the severity of iodine deficiency in Latgale region was highest and in Kurzeme lowest.

Conclusions and Recommendations

The analysis of the national neonatal TSH screening data for 2000-2002, together with a more limited study of school-aged children in 2000, leads to the conclusion that that L, according to theWHOICEF/ICCIDD guidelines, is characterized as a country with mild to moderate iodine deficiency. The present analysis identified a trend toward reduced proportions over time in the newborns with elevated TSH, which may be due to some efforts so far made in Latvia to increase the supply of iodized salt in the nation.

The present study demonstrates that the ongoing neonatal TSH screening in Latvia offers a solid and comprehensive source of information for assessing and classifying the iodine nutrition status in the population. Compared to urinary iodine excretions among school children, newborn TSH levels represent the most direct and best available signal of the functional penalty of iodine deficiency during human reproduction, i.e. the period of life of most concern for the damage of iodine deficiency in the developing child’s brain cells. Since the neonatal TSH screening in Latvia is established and fully functional, it offers a valuable tool for monitoring trends over time associated with improved iodine nutrition in the population.


Semi-annual analysis of the neonatal TSH data would offer a key tool to the national IDD Committee in monitoring that the national IDD elimination effort through salt iodization remains successful. Continued oversight of iodine nutrition in a population is a somewhat delicate task, since the range of optimum dietary intake of iodine in a population is not unlimited. Deficient as well as excessive dietary iodine intake in a population may have harmful consequences for thyroid function.
The laboratory of the Genetic Center at the Gailezers Republican Children Hospital in Riga, where the blood spots are processed, has adequate performance for congenital hypothyroidism screening as certified by the international quality assurance service from the Centers of Disease Control & Prevention in Atlanta, USA. Using this TSH screening system for monitoring the permanent disappearance of iodine deficiency in Latvia would not require complicated institutional arrangements, nor would it require much investment which may be bothersome for the IDD Committee budget. The analyst at the Genetic Center may need some training and guidance in using the available statistical package (within the TSH assay Manufacturer’s software) for analysis and reporting of the semi-annual consolidated TSH results to the Latvian IDD Committee.

Should our recommendation be accepted that the data from national newborn TSH screening be utilized for permanent monitoring of optimum iodine nutrition in Latvia, it is advised that the Gailezers Hospital Laboratory seeks assistance from the Centers for Disease Control & Prevention to be provided with TSH quality assurance blood spots in the relevant range of the cut-off used for this purpose, i.e. 5mIU/L, additional to the samples at 25mIU/L that are currently provided. Independent certification of adequate performance at this lower level of elevated neonatal TSH tests would improve the confidence in the monitoring information acquired.


References
De Escobar, GM. The role of thyroid hormone in fetal neurodevelopment. Journal of Pediatric Endocrinology & Metabolism 14; 1453 – 1462, 2001

Delange F. Neonatal thyroid screening as a monitoring tool for the control of iodine deficiency. Acta Paediatrica Supplement 432; 21 – 24, 1999

Maberly GF, Haxton DP, van der Haar F. Iodine Deficiency: Consequences and Progress Toward Elimination. Food and Nutrition Bulletin 24(4); S89 – 96, 2003

Mikelsaar RV, Viikmaa M. Neonatal thyroid-stimulating hormone screening as an indirect method for the assessment of iodine deficiency in Estonia. Hormone Research 52; 284 – 286, 1999

Nordenberg DF, Ratajcsak R, Rybakova M, Tylck D, Maberly GF. Neonatal hypothyroid screening programs: A sensitive IDD surveillance system. In: Stanbury JB, Ed. The Damaged Brain of Iodine Deficiency: Cognitive, Behavioral, Neuromotor and Educative Aspects. Cognizant Communication Corporation, New York, 279 – 283, 1994

Selga G, Sauka M, Gerasimov G. Status of iodine deficiency in Latvia reconsidered: Results of nation-wide survey of 587 schoolchildren in the year of 2000. IDD Newsletter 16(4); 54, 2001

Stanbury JB. The Damaged Brain of Iodine Deficiency: Cognitive, Behavioral, Neuromotor and Educative Aspects. Cognizant Communication Corporation, New York, 1994

WHO/UNICEF/ICCIDD. Assessment of Iodine Deficiency Disorders and Monitoring their Elimination. A guide for programme Managers. World Health Organization, Geneva, pub WHO/NHD/01.1, 2001



Acknowledgements

I would like to express my gratitude to the Ministry of Health of Latvia, in particular to Dr. Inga Smate, the Head of Epidemiological Safety and Nutrition Department and Dr. Lelde Vancovica of the Mother and Child Health Department for giving me access to the information in the Ministry of Health, the Gailezers Genetic Center and State Statistical Department. Special thanks are due to Dr. Rita Lugovska and Dr. Parsla Vevere at the Gailezers Genetic Center for their supportive understanding and for providing the data.

I would like to thank my thesis advisor Dr. Frits van der Haar for his valuable assistance throughout the process. He encouraged my travel to Latvia and put me in contact with the Ministry of Health of Latvia.


I would like to thank my family and my friends, especially the former Muskie students Ilze Jecabsone from Latvia, with whom I stayed in Riga, and Natalya Volkova from Ukraine for their strong moral support and encouragement throughout the entire period.






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