Urinary iodine excretion and antiperoxidase enzyme antibody in goitrous and healthy primary school children of Arak, Iran

Abstract

To determine urinary iodine excretion (UIE) and antiperoxidase enzyme antibody (anti-TPO Ab) in primary school-age children living in Arak, Iran, in 2005, after 10 yr of iodized salt distribution in an effort to ameliorate iodine deficiency. Through an observational, case-control study and by means of satisfied sampling, 6520 primary school children were examined for goiter, and then 193 goiterous children (case) and 151 healthy (control) children were assessed as representative samples for thyroid function tests, antiperoxidase antibody, and urinary iodine excretion. Normal values of anti-TPO Ab were <40 U/ml and high values >75 U/ml. Normal values of urinary iodine concentration were > or =10.0 microg/dl, and severe iodine deficiency were <2 microg/dl. The data were analyzed and compared by the Chi- Square tests and Mann-Whitney U in SPSS software; p-values <0.05 were considered statistically significant. Total mean prevalence of goiter was 5.2%, ranging from 3.6 to 6.4% in different schools. The prevalence of goiter increased with age; it was 3% in children aged 6-7 yr and 6.3% in children aged 11 yr (p<0.001). Mean iodine urinary concentration was 16.36 microg/dl (+/-1.58). No difference was seen between the mean urinary iodine in girls (17.30+/-3.80 micorg/dl) and boys (15.72+/-2.72 microg/dl). No difference was seen between the mean urinary iodine in goiterous and healthy school children (17.4+/-3.7 microg/dl vs 15.3+/-3.18 microg/dl, p=0.78). About 49.5% of school children had UIE<10 microg/dl and 28% had UIE<5 microg/dl. High levels of anti-TPO Ab were found in 21 school children (18 goiterous vs 3 healthy children, p=0.01) resulting in a total prevalence of 6.1%. In females, the prevalence was 1.3 times higher than in males (male:female ratio 3/4). Thirteen out of 21 (62%) children with positive antibodies had significant goiter (grade 2), and 5 (24%) had small goiter (grade 1), whereas only 3 children (14%) had normal thyroid size (p=0.001). If urinary iodine concentration is considered an index of total body iodine content, this study demonstrated that prolonged iodized salt intake has minimized the occurrence of iodine deficiency goiter and now autoimmune thyroid enlargement is one cause for continuous goiter in primary school children, although there are unknown etiologies that need to be considered in further studies.