Reference ranges for thyrotropin in the serum of full-term neonates--compared with the ranges for full-term neonates with various post-partal adaptation disorders, and premature neonates.

The "IMx hTSH ultrasensitive test" from Abbott Laboratories is a new method for the determination of thyrotropin. Its introduction for the purpose of hypothyreosis screening led to the present investigation of the reference ranges in full-term and premature neonates. In a total of 1712 healthy neonates, the reference range for serum thyrotropin on the 5th day post partum was 0.4-9.05 mU/l (median value 1.90 mU/l). In contrast, 64 full-term neonates with various post-partal adaptation disorders showed a significantly lower serum thyrotropin concentration on the 5th day post partum (0.14-6.39 mU/l; median value 1.60 mU/l). Serum thyrotropin was also determined on the 7th and 14th day post partum in 131 premature neonates with birth-weights below 2500 g. In the birth-weight range 1500- < 2500 g, the median values for serum thyrotropin were 2.35 and 2.12 mU/l, respectively. A negative correlation (r = -0.3019) was found between the birth-weight and the serum thyrotropin concentration on the 14th day post partum. In two premature neonates with birth-weights less than 800 g, the serum thyrotropin concentrations were conspicuously high (18.6 and 28.0 mU/l) on the 14th day post partum.