Résumé
PURPOSE: To establish reference ranges for thyroid hormone concentrations in premature infants, we measured T4 and thyroid stimulating hormone (TSH) concentrations and analyzed the relation to gestational age and birth weight. METHODS: Serum T4 and TSH concentrations were measured by radioimmunoassay for 391 premature infants born in Sanggye Paik Hospital for two years and eight months. RESULTS: Gestational age of the subjects was 33.3 +/- 2.4 weeks (range : 26-37 weeks). Birth weight was 2,016 +/- 520g (range : 880-3,510g). Sampling date was 10.5 +/- 8.6 day (median value 8 day). Serum T4 concentrations for the gestational age 26 to 28, 29 to 31, 32 to 34 and 35 to 37 week groups were 4.8 +/- 3.6, 5.6 +/- 3.6, 6.4 +/- 4.4 and 7.0 +/- 4.6 microgram/dl, respectively. Serum T4 concentrations for the birth weight below 1,500, 1,500 to 1,999, 2,000 to 2,499 and above 2,500g groups were 5.7 +/- 3.8, 5.8 +/- 3.6, 6.4 +/- 4.6 and 8.1 +/- 5.1 microgram/dl, respectively. Serum TSH concentrations for the gestational age 26 to 28, 29 to 31, 32 to 34 and 35-37 week groups were 6.5 +/- 3.0, 7.2 +/- 6.1, 5.8 +/- 5.0 and 5.6 +/- 5.1 mIU/ml, respectively. Serum TSH concentrations (mean +/- SD) for the birth weight below 1,500, 1,500 to 1,999, 2,000 to 2,499, above 2,500g groups were 8.3 +/- 6.8, 5.7 +/- 4.3l, 5.5 +/- 5.1 and 5.6 +/- 5.2 mIU/ml, respectively. Serum T4 concentrations correlated positively with gestational age (y=0.31x-3.7, R2=0.03, P<0.05) and birth weight (y=0.001x+3.33, R2=0.33, P<0.05). Serum TSH concentrations correlated negatively with gestational age (y=-0.25x+16.1, R2=0.01) and birth weight (y= -0.001x+10.6, R2=0.01). CONCLUSION: Serum T4 concentration in premature infants positively correlated with gestational age and birth weight. Transient elevation of serum TSH concentration was normalized at follow- up test. We recommend that a reference value should be set according to gestational age and birth weight.