Evaluation of three thyroid-function screening tests for detecting neonatal hypothyroidism.

Three thyroid-function detection methods were evaluated concomitantly for possible application as routine screening tests for the early diagnosis of neonatal hypothyroidism. Dried capillary-blood thyroxine (T4) was measured on eluted filter-paper discs for 9734 3-5-day old neonates. Serum T4 and thyroid-stimulating hormone (T.S.H.) assays from cord blood were studied as alternative screening tests on 4911 and 3733 infants, respectively. To avoid false-negative results, neonatal blood-T4 and cord serum-T4 screening methods were followed up for the lower 10th and 6th percentile, respectively. This resulted in a false-positive recall incidence greater than 92% owing to various additional factors which also influence T4 levels: thyroxine-binding-globulin deficiency, prematurity, and maternal drug ingestion. In marked contrast, cord T.S.H. as an initial screening test had a higher specificity and sensitivity for the diagnosis of primary hypothyroidism with the two affected cases, having values greater than 70 muU/ml (with only 0-24% of the screened population having values greater than 50 muU/ml). In order to avoid the impracticably high recallrate and false-positive incidence resulting from an initial T4 screening test, and to reduce the estimated follow-up recall to less than 0-2% of the screened infant population, it is recommended that infants with low T4 be selected for a supplementary T.S.H. screening test.