Serum Thyroxine (t4) and Thyroid Stimulating Hormone (tsh) Levels in Cord Blood of Newborns in Lahore

Objective: The primary aim of this study was the early detection and treatment of hypothyroidism in neonates. This paper describes the determination of cord blood serum T4 and TSH levels, their mean levels, reference ranges and interrelationship. Design: Retrospective analysis of serum T4 and TSH levels in 1153 cord blood samples collected and analyzed during July 1998 to June 2000. Setting: Centre for Nuclear Medicine (CENUM), Mayo Hospital, Lahore. Patients: Cord blood samples of unselected neonates born at Lady Aitchison Hospital, Lady Willingdon Hospital & Government Mian Munshi Hospital, Lahore, randomly collected immediately after delivery. Main outcome measures: Cord serum T4 and TSH levels, their respective means and reference range. Results: Mean ( ± SD) T4 level in cord blood serum was 115 ±36 nmol/L (range: 15-350 nmol/L) and mean TSH level was found to be 5.6 ±5.1 mIU/L (range: 0.05 150). The reference range for T4 and TSH was 49-189 nmol/L and 0.4-17.6 mIU/L respectively. A trend in T4 and TSH levels distributions towards higher values was noted. Serum T4 and TSH levels were not correlated significantly. Except at lowest and highest levels no reciprocal relationship between T4 and TSH levels was found as is observed in adults. T4 and TSH levels in 90% neonates were between 60-173 nmol/L and 1.0-14.2 mIU/L respectively. Conclusion: In most neonates, level of cord serum T4 was independent of TSH level. Mean T4 and TSH levels and their normal ranges were lower as compared to an iodine-sufficient country like USA. In 11.4% of neonates TSH levels were above 10 mIU/L, corresponding to mild degree of iodine deficiency disorders in