 |
|
Brief Reports Indian Pediatrics 2001; 38: 901-905 |
|||||||||||||||||||
|
Comparison of Urinary Iodine Excretion and Goiter Survey to Determine the Prevalence of Iodine Deficiency |
|||||||||||||||||||
Sanjiv Kumar Bhasin Iodine deficiency disorders (IDD) constitute a major public health problem in India. It is estimated that nearly 200 million people are exposed to the risk of IDD. It is also estimated that 71 million population is suffering from goiter and other IDD(1). IDD is also a public health problem in the National Capital Territory of Delhi(2). Salt iodization is the most successful measure for prophylaxis of IDD and is an appropriate vehicle because it is consumed universally by all socio-economic groups(3). Under the National IDD control program, iodized salt containing 15 ppm of iodine is made available to the beneficiaries(4). An earlier study conducted in this urban slum in East Delhi had shown that only 13% of the families of school children were using salt having iodine content of more than 15 ppm. A total of 4.6% families were using salt with nil iodine content and 82.4% were using salt with some iodine content but less than 15 ppm(5). The two most valuable means for assessing the severity of iodine deficiency in a given area are: (i) the prevalence of goiter, and (ii) the urinary excretion of iodine. As the IDD prevention programs progress, goiter rates may become progressively less useful and urinary iodine levels become more useful for assessing the magnitude of IDD. The present study was, therefore, conducted amongst school children to compare the Urinary Iodine Excretion (UIE) levels with the goiter survey to determine the prevalence of iodine deficiency. Subjects and Methods The present study was cross-sectional in design and was undertaken in Nand Nagri in the year 1996 in East Delhi. This area is the field practice center of the Department Community Medicine. Nand Nagri slum has a population of approximately 64,000. There are four primary schools in Nand Nagri. These have a morning shift for boys and an evening shift for girls. These schools are Government schools run by Municipal Corporation of Delhi (MCD). For the present study one school was selected by using random sampling technique with the help of random number table. All school children between the age groups of 8-10 years of both sexes were examined for the presence of goiter using the new standard classification. The children were collected in their classes from class III to class V. Their ages were verified from the school register and only children belonging to the age group 8-10 years were included in the study. The children were examined on three consecutive days and only those children who were absent on all the three days were excluded from the study. A total of 940 school children were examined. The sample size was calculated on the basis of prevalence of 10% goiter rate at 20% maximum likely error. This gave the sample size required to be 900. All the school children were examined by the first author, who is trained in conducting goiter surveys. The criteria of WHO was used to define various grades of goiter(6,7). Casual urine samples of 132 systematically randomly selected children were collected in screw capped plastic bottles for the assessment of Urinary Iodine Excretion (UIE) levels. In each class urine sample of every seventh child was taken. By using a random number table, the first child was selected. Subsequently, every seventh chld was included for assessment of UIE levels. The samples were transported the same day to AIIMS, New Delhi. These samples were refrigerated for an average period of 100 days (range 80-115 days). The standard alkaline ashing method was used to estimate the UIE(8,9) levels at Human Nutrition Unit of AIIMS, New Delhi. Results A total of 940 school children were examined. There were 502 boys (53.4%) and 438 girls (46.6%). The children aged 8 years, 9 years and 10 years were 312 (33.2%), 301 (32.0%) and 327 (34.8%), respectively. Children in classes III, IV and V were 347 (36.9%), 329 (35.0%) and 264 (28.1%), respectively. The total number of children having grade-I goiter were 59 (6.2%) and those with grade-II goiter were 3 (0.3%). Eight hundred and seventy eight children (93.8%) did not have any goiter. UIE was estimated on 132 randomly selected children only. The mean urinary iodine level was 9.457 µg/dl (SD 5.407). Fifty three (40.1%) of these children had normal UIE levels of more than 10 µg/dl. Twenty four (18.2%) children had moderate degree of iodine deficiency as indicated by UIE levels between 2.0 to 4.9 µg/dl, while 55 (41.7%) children had UIE levels between 5.0 to 9.9 µg/dl indicating mild degree of iodine deficiency. No child had UIE levels less than 2.0 µg/dl (indicating severe degree of deficiency). The median UIE in these children was 8 µg/dl. Considering urine iodine estimation levels as gold standard for finding out the iodine status, the sensitivity and the positive predictive value (PPV) of goiter survey were found to be only 6.32% and 50.0%, respectively (Table I). Discussion The prevalence of goiter in the present study was 6.5%. Clearly, the prevalence of goitre in Delhi has been declining over the years. In 1980, Pandav et al. reported goiter prevalence to be 55.2% in schoold children in Delhi(10). Much lower prevalence of goiter, i.e., 8.6% and 20.5% have been reported by two recently conducted studies in Delhi(11,12). Moreover, in both these recently conducted studies in Delhi the prevalence of grade II goitre has been steadily declining. Pandav et al.(12) reported prevalence of grade-I goiter as 17.3% and grade-II goiter as 3.2%. Kapil et al.(11) reported a prevalence of 8.5% for grade-I and 0.1% for grade-II goiter. Similarly, in our study, more than 95% of those having goitre had grade I goiter which further shows the declining trend of the problem. A declining trend of iodine deficiency is also evident from the estimation of UIE over a period of time in different studies done in Delhi. Pandav et al (10) in 1980 reported that 62.5% of the urine samples had iodine levels less than 50 µg/L. Likewise Sharma et al.(13) in 1988 reported urinary iodine levels to be less than 75 µg/L. However, both these studies used mean instead of median UIE levels and, threrefore, their findings may not be representative. The reason for this is that the UIE levels from populations usually are not normally distributed and, therefore, for such measurements the median values should be used rather the mean values(14). In our study, the median UIE level was 8 µg/dl. The median UIE levels in the present study are much lower than the median UIE levels of 17 µg/dl and 19.8 µg/dl reported in the two recently conducted studies in Delhi(11,12). This could be due to the fact that all the children belonged to extremely poor socio-economic strata of one slum area of Delhi while in other studies a sample for the whole of Delhi having a mixture of populations of all socio-economic strata of children was used. Our findings are also consistent with the use of salt containing iodine content less than 15 ppm by majority of this population(5). These findings thus show that iodine deficiency disorders despite showing a declining trend continue to be a public health problem in some parts of Delhi, as revealed by low UIE levels.
Sensitivty of goiter survey = 5 X 100/79 = 6.32% Specificity = 48 X 100/53 = 90.56% We would like to point out that inaccuracies are likely to creep in if only goiter prevalence rates are used to ascertain the iodine status of the population. The fact that 59.9% of the school children in our study were detected to be having UIE levels less than 10 µg/dl as compared to only 6.5% prevalence of goiter indicates the poor sensitivity of the latter in comparison to former. Thus, to obtain a true picture of the problem and to know the progress made by the National Iodine Deficiency Disorders Control Program, a regular monitor-ing using UIE levels is recommended. Contributors: SKB and PK coordinated the study. SKB will ac as the guarantor for the paper. Data collection was done by SKB and KKD. PK analysed the data. All the authors were involved in the drafting of the paper. Funding: None. Competiting interests: None stated.
|
