Thyroxine and Illness Severity in Very Low-Birth-Weight Infants

The objective of this study was to determine the relationship between thyroxine (T₄) and illness severity in a population of preterm infants. We investigated a cohort of infants with birth weights 1,500 g or less from a single level III neonatal intensive care unit who received a minimum of one cranial sonogram to screen for intraventricular hemorrhage (IVH) and one newborn screen for T₄ during a 2-year period, (n = 284). The Score for Neonatal Acute Physiology (SNAP) was used to measure illness severity. T₄ and SNAP were investigated in relationship to mortality, IVH, and severe IVH. T₄ correlated inversely with SNAP (R =-0.46, p < 0.01). Infants with severe IVH and mortality had lower T₄ and higher SNAP scores when compared to infants without these conditions. These differences persisted after controlling for the confounding effect of gestational age. Analysis of receiver operator curves indicated that high SNAP and low T₄ were equivalently associated with IVH, severe IVH, and mortality. Our data indicate that T₄ is associated with illness severity in very low-birth-weight infants. Low T₄ levels and high SNAP scores are both associated with the outcomes of IVH and mortality in very low-birth-weight infants.