[Frequency of subclinical hypothyroidism among healthy children and those with neurological conditions in the state of Mérida, Venezuela].

The purpose of this study was to investigate and to compare the frequency and possible aetiology of subclinical hypothyroidism (SH) in healthy and sick children developing neurological disorder changes. One hundred and eighty-seven male and female children between 1 month and 4 years old, 64 with and 123 without neurological disorders, were studied in the state of Mérida, Venezuela. Serum levels of thyrotropin (TSH), free thyroxine (FT4) and urinary iodine were measured by immunofluorescence and by the Sandell-Koltoff's method. Children were diagnosed as having SH if they had high levels of TSH and normal levels of FT4. Antithyroglobulin and antiperoxidase antibodies were measured in children with SH. To establish the frequency of SH, the TSH reference levels on the commercial kit (> 3.8 uU/mL) and the TSH reference levels of our group of healthy children were used. The latter was calculated (X + 2SD) from the values of TSH in the 123 healthy children (> 4.98 uU/mL). The frequency of SH in all children was of 15% when the TSH level from the commercial kit was used and of 6.4% when it was of our group of children (p < 0.001). The frequency of SH value was of 17.2% in children with neurological disorders and of 13.8% in healthy children when the commercial kit's TSH level was used. The frequency of SH in children with neurological disorders was of 7.8% and of 5.7% in healthy children, according to our TSH reference level. This difference was not statistically significant. No significant differences were found in the urinary iodine levels or in the presence of thyroid autoantibodies among the two groups of children with or without SH. There was no association between iodine urinary levels, presence of SH and neurological disorders. We conclude that: 1. In order to make suitable SH level diagnosis in children, we must establish our own levels of reference for TSH. 2. The frequency of SH in children from Mérida state is high, being slightly higher in children with neurological disorders. 3. The aetiology of SH is not due to iodine deficiency or immunological factors.