SCREENING FOR CONGENITAL HYPOTHYROIDISM

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Abstract
In a pilot screening program for congenital hypothyroidism, PKU [phenylketonuria] filter paper blood samples from 20,000 infants born in Stockholm [Sweden] were analyzed for TSH [thyrotropin] and T4 [thyroxine] to identify optimal conditions for routine nation-wide screening. Among 160 infants with positive screening tests, 7 infants (group I) had true-positive results, 6 had primary and 1 secondary hypothyroidism. The 153 infants with false-positive tests were divided into group II: 74 infants with an isolated increased TSH level; group III: 71 infants with an isolated decreased T4 concentration; and group IV: 8 ifants with increased TSH and decreased T4 levels. In group I, the clinical signs and symptoms of hypothyroidism varied when the diagnosis was made at 3 wk of age. The median hypothyroid index score was 8 (range 0-18). In groups II-IV, most infants showed very few signs of hypothyroidism. The median hypothyroid index scores were 1, 1 and 0, respectively. Clinical findings were of little value in the individual case for distinguishing true from false positive screening tests. Nation-wide screening should be based on TSH analyses of PKU blood samples, with a cut-off level corresponding to 50 mU/I of plasma. Recall frequency will be < 0.1%.