Abstract
Elevated thyrotropin (TSH) levels in critically ill extremely premature infants have been attributed to transient hypothyroidism of prematurity or non-thyroidal illness syndrome. We evaluated the hypothesis that relatively high TSH levels in the first 2 postnatal weeks follow recovery from systemic inflammation, similar to non-thyroidal illness syndrome. The study was conducted in 14 Neonatal Intensive Care Units and approved by each individual Institutional Review Board. We measured the concentrations of TSH and 25 inflammation-related proteins in blood spots obtained on postnatal days 1, 7, and 14. We then evaluated the temporal relationships between hyperthyrotropinemia (HTT), defined as a TSH concentration in the highest quartile for gestational age and postnatal day, and elevated levels of inflammation-related proteins. 880 newborns less than 28 weeks of gestation were included. Elevated concentrations of inflammation-related proteins during the first or second week did not precede day-14 HTT. Systemic inflammation on day 7 was associated with day-14 HTT only if inflammation persisted through the end of the 2 week period. HTT frequently accompanied elevated concentrations of inflammation-related proteins on the same day. The hypothesis that HTT follows recovery from severe illness, defined as preceding systemic inflammation, is weakly supported by our study. Our findings more prominently support the hypothesis that TSH conveys information about concomitant inflammation in the extremely premature newborn.