Evaluation of thyroid status of infants in the intensive care setting

Previous studies report the spectrum of thyroid function abnormalities in critically-ill neonates. In this study, we evaluated the thyroid status in critically-ill neonates, and determined whether thyroid function abnormalities are more common in sick neonatal infants.

In a prospective cohort study, 67 critically-ill infants from the Neonatal Intensive Care Unit (NICU), affiliated to Shiraz University of Medical Sciences, were entered into our study. Of all the included neonates, 33 were premature and seven were under 28 weeks of gestation. In addition to the routine thyroid-stimulating hormone (TSH)-screening (capillary specimen), serum free triiodothyronine (FT3), free thyroxine (FT4) and TSH were checked using radioimmunoassay kit twice (during critical illness and before discharge from the NICU).

It was observed that abnormal TSH levels (screening test) were about 40-fold higher in critically-ill neonates compared with healthy neonates, while more than four-fifths of them were detected in the second sampling done after recovery. The mean FT3 was significantly lower during the critical illness and it increased after recovery (2.537 and 3.232 pg/ml, respectively). Mean FT4 and mean TSH during the illness and after recovery did not have any significant difference.

Thyroid function abnormalities are more common in infants under intensive care and most of them manifested as "euthyroid sick syndrome"; abnormal screening tests may be due to the transient elevation of TSH during recovery from illness. Therefore, only in cases in which TSH rises more than 15-20 mIU/L or TSH remains high for a month or longer, that treatment is needed, while other cases must be followed up by serial determination of TSH and FT4. The levels of FT3 and FT4 during the illness were not affected by the duration and severity of the illness.