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Iodine deficiency constitutes a major nutrition problem worldwide [1]. The youth are the most susceptible to iodine deficiency and its consequences, as iodine is essential for normal growth and development. The most deleterious effect of iodine deficiency is mental retardation and it is reported to be associated with a loss of intelligence quotient [2]. In Pakistan, iodine deficiency is known to exist in the northern region including the Khyber Pakhtunkhwa province and Azad Jammu and Kashmir [3]. For preventing this, salt iodization programs were started in 1989 by the National Iodine Deficiency Disorder (NIDD) program in Pakistan, but a high number of the rural population still uses non-iodized salt [4]. Consumption of iodized salt in Pakistan, last measured in 2011, was found in 69.20% of the households, according to the World Bank [5]. Iodine deficiency lowers the circulating T4 and raises the serum thyroid stimulating hormone (TSH), due to which iodine-deficient populations generally have higher serum TSH concentrations compared to iodine-sufficient groups. Screening in developed countries is directed at detecting neonates with congenital hypothyroidism (TSH >40 mIU/L in serum) and not at assessing iodine status. However, serum TSH can also be used to assess the iodine status of a population.
Serum TSH is not a practical marker for iodine deficiency in school-going children and adolescents, as the serum TSH values of iodine sufficient and insufficient groups overlap. Serum TSH is reported to be a valuable indicator for iodine deficiency in neonates as they have low total body iodine content and high turnover. This higher turnover of iodine leads to increased TSH levels, and its response is enhanced in iodine deficiency [6]. Hence, TSH levels are increased in iodine-deficient neonates and this phenomenon is called transient hypothyroidism [7]. Therefore, evaluating elevated TSH level is a valuable indicator of the severity of iodine deficiency in neonates, if performed within 48–72 hours of life [7].
The World Health Organization (WHO) in collaboration with United Nations International Children's Emergency Fund (UNICEF), and the International Council for Control of Iodine Deficiency Disorders (ICCIDD) recommend that serum TSH levels >10 mlU/L are mild elevations and are proportional to the degree of iodine deficiency [8]. The consensus statement states that when a sensitive TSH assay is used on samples collected three to four days after birth, a <3% frequency of TSH values >10 mlU/L indicates iodine sufficiency in a population [9].
The present study aimed to evaluate the iodine status in neonates tested at our center using the current WHO/UNICEF/ICCIDD criteria for iodine deficiency, i.e., >3% of neonates exhibiting TSH values >10 mIU/L indicates iodine deficiency.
Retrospective analysis of laboratory data from patients tested for serum NTSH from January to December 2013 was conducted at the Section of Chemical Pathology, Department of Pathology and Laboratory Medicine, Aga Khan University Hospital. For all subjects, only initial test results were included and repeated testing results were excluded. Our center is a tertiary care center based in Karachi with both urban and rural patients. Most females registered for delivery belong to urban areas. Additionally complicated cases from rural areas and peripheral regions are also referred to our center. In the present study, neonates were discharged after 48 hours and samples are obtained right before discharge. To maintain confidentiality, instead of the patient identification details a code was assigned. Exemption was sought from the institutional ethical review committee (3344-Pat-ERC-14).
For TSH analysis, 2 mL of blood was collected in a gel separator tube and sent to a laboratory. At the laboratory, serum was separated and analyzed by an automated analyzer ADVIA Centaur (Siemens Diagnostics, NY, USA), using a chemiluminescence immunoassay technique. Three levels of quality control materials were run with each batch of samples and the laboratory participated in a proficiency testing surveys of the College of American Pathologist twice a year with >80% performance compared with peer group. The optimal TSH was 1–39 mIU/L, while a value ≥40 mIU/L was labeled as congenital hypothyroidism.
According to the WHO/UNICEF/ICCIDD ‘consensus criteria’ more than 3% prevalence of serum TSH ≥10 mIU/L in a population is considered as an indicator of iodine deficiency. A frequency of 3–19.9% indicates mild iodine deficiency. Frequencies of 20–39.9% and above 40% indicate moderate and severe iodine deficiency, respectively [5].
The statistical analysis was performed using the Statistical Package of Social Sciences (SPSS) version 19. For examining the distribution of data, Kolmogorov-Smirnov test was performed. Statistical analyses were performed for continuous variables whereas data were analyzed for the frequency of samples from each group (<1 mIU/L, 1–10 mIU/L, 10–40 mIU/L, >40 mIU/L).
Within a period of one year, a total of 11,597 samples were analyzed for neonatal serum TSH, the median (25 percentile, 75 percentile value) age of neonates was 2.0 days (0.5–3.5). Nearly 90% (N=10,441) of the neonates tested for serum NTSH were born at the Aga Khan University Hospital, whereas the remaining samples were received from outpatient clinics. The distribution of data was skewed on Kolmogorov-Smirnov test (P<0.001).
The overall median TSH level was 3.38 mIU/L (149.99). Optimal levels of TSH were found in 86% of the neonates, and TSH level <1 mIU/L was found in 6.4% of the neonates Congenital hypothyroidism was suspected in 0.3% of the neonates with a serum TSH value ≥40 mIU/L. Hyperthyroidism was suspected in 0.1% of the neonates with serum TSH <0.1 mIU/L. Of the neonates, 7% (N=916) showed TSH ≥10 mIU/L, which is higher than the recommended WHO criteria for mild endemicity for iodine deficiency in the population. The distribution of serum TSH and the frequency of subjects with deficiency are shown in Table 1.
In the present study, we observed that despite implementation of NIDD programs, iodine deficiency is still prevalent in our population, with nearly 8% neonates tested at 2nd day of life exhibiting serum TSH >10 mIU/L. This indicates a ‘mild iodine deficiency’ according to the criteria. The national nutrition survey 2011 (NNS 2011) conducted in Pakistan, reported that children aged 6–12 years had median urinary iodine levels of 126 µg/L, but adequate iodine levels (>100 µg/L) were found in only 63.3% of the children [1011]. This survey also reported that 7% of school-going children (6–12 years) had either palpable or visible goiters on clinical examination, which is another indicator for iodine deficiency status. Our study findings are comparable with the prevalence of goiter reported by NNS in 2011; however, the actual figures of iodine status in our population may be much poorer as the urinary iodine estimation shows a higher prevalence of iodine deficiency.
Our TSH method is a fourth generation or ultrasensitive assay that detects very low quantities of NTSH.
Pakistan is the 6th most populous country in the world, with a population of about 180 million. More than 42% of the Pakistani population is aged <14 years [12]. Priorities for child healthcare have focused on infectious diseases, malnutrition, and other communicable diseases. There is lack of government commitment to invest in correcting the micronutrient status. Salt iodization programs in our country were started in 1989, but the reported use of iodized salt for cooking is 39.8% (NNS 2011) [10]. The main reasons for this include the absence of legislations regarding salt iodization and the introduction of these programs only in large scale salt processors. Since 70% of our population resides in rural areas and uses salt sourced from small scale salt processors, our population is not benefitting from these programs. Moreover, there is no proper mechanism for assessing the efficiency of such programs and for educating the public regarding the benefits of using iodized salt in regular diet. Although the main responsibility for a successful national salt iodization programme rests with government officials and international agencies to assist governments with appropriate advice, funding, and training, it is high time that private sector agencies come forward and spread this message.
There are some limitations to our study. Here, urinary iodine concentration was not measured for assessing iodine status. Although urinary iodine measurement is superior to serum TSH for assessment of iodine status, but the method for its measurement is inductively coupled with Mass Spectrometry, and thus, requires expertise and cannot be performed routinely [13]. Contrarily, serum TSH assessment can reliably replace urine iodine estimation if performed using an accurate and precise methodology with neonatal samples collected less than 48 hours after birth [14]. Since the current study included only laboratory data of serum TSH and the prevalence of iodine deficiency can be increased or decreased if actual urinary iodine is measured.
In conclusion, iodine deficiency is prevalent in Pakistan as shown by the frequency of high serum TSH levels in this study. Eradication of iodine deficiency must be made a national goal, indicating that there is a need for effective intervention programs and incre-asing awareness among the public regarding the use of iodized salt. We should particularly aim to improve the iodine status of young children and pregnant ladies to prevent consequences of iodine deficiency and improve fetal outcomes [15].
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