School based screening for hypothyroidism in Down's syndrome by dried blood spot TSH measurement.

OBJECTIVE To determine the feasibility of annual hypothyroid screening of children with Down's syndrome by measuring thyroid stimulating hormone (TSH) on dried blood spots at school, and to describe the outcome in positive children. DESIGN Establishment of a register of school children with Down's syndrome, and procedures for obtaining permission from parents, annual capillary blood samples, TSH measurement, and clinical assessment of children with TSH values > 10 mU/litre. SUBJECTS All school age children with Down's syndrome within Lanarkshire and Glasgow Health Boards during 1996-7 and 1997-8. RESULTS 200 of 214 school children with Down's syndrome were screened. Four of the unscreened children were receiving thyroxine treatment, and only 5 remained unscreened by default. 15 of the 200 children had capillary TSH > 10 mU/litre, and all but 1 had evidence of Hashimoto's thyroiditis. Seven of the 15 children started thyroxine treatment immediately, 6 with a pronounced rise in venous TSH and subnormal free thyroxine (fT4), and one with mildly raised TSH and normal fT4 but symptoms suggesting hypothyroidism. Eight children with mildly raised venous TSH and normal fT4 were left untreated; 1 year after testing positive, fT4 remained > 9 pmol/litre in all cases, but 4 children were started on thyroxine because of a rise in TSH. TSH fell in 3 of the 4 remaining children and there was a marginal rise in 1; all remain untreated. The prevalence of thyroid disease in this population is >/= 8.9%. CONCLUSION Dried blood spot TSH measurement is effective for detecting hypothyroidism in Down's syndrome and capillary sampling is easily performed at school. The existing programme could be extended to the whole of Scotland within a few years.