The relationship between thyroxine level and short term clinical outcome among sick newborn infants

Premature and critically sick infants frequently experience several interventions, including blood transfusions, parentral nutrition, and prescriptions during hospitalization that could affect the result of thyroid function test. This study aims to investigate the correlation between thyroxine level and clinical short term outcome among the newborn infants in the neonatal intensive care unit (NICU). We assessed serum levels of thyroxine and thyroid stimulating hormone of 99 neonates who were admitted in the NICU from September 1(st) 2004 to March 30(th) 2005. Number of patients with low thyroxin level (less than 6.5 µg/dl) was determined and the relation between serum total thyroxine level and birth weight, gestational age, duration of hospitalization, clinical diagnosis, and final outcome was investigated. Short term outcome was considered as duration of hospitalization and discharge alive from hospital. Prevalence of hypothyroxinemia was 26 percent. Later assessment of thyroxine level within 3 weeks revealed normal level of this parameter (8.12 µg/dl ±1.36). Patients with lower gestational age and lower birth weight had lower thyroxine level (7.15 µg/dl ±2.56, and P=0.03, 6.72 µg/dl ±3.03, and P=0.08). Low thyroxine level was not associated with adverse short-term clinical outcome (mortality rates; 3(11%) and 9(12%), and duration of hospitalization among 17.7±9.8 vs 16.7± 13.0 in patients with hypothyroxinemia and low thyroxine level respectively). Hypothyroxinemia has considerable prevalence in neonatal intensive care setting and is related with lower birth weight and gestational age. Whether thyroxin levels are a marker or mediator of short term clinical outcome remains to be determined by further studies.