Thyroid Function Tests in Critically Ill Children; Any Correlation with Disease Severity or Outcome?

Background: Sick euthyroid syndrome (SES) is the most common endocrine disorder in critically ill patients. It has been shown that the decrease in T4 levels correlates with disease severity and prognosis. Whether SES is a compensatory response to the disease course or needs to be treated is not known yet. Objectives: To our knowledge, there are only a few studies on critically ill infants and children investigating the correlation between thyroid function and disease severity as well as its outcome. Therefore, this study aimed to investigate thyroid hormone levels in critically ill patients. Methods: In this study, thyroid function tests including thyroid stimulating hormone (TSH), total T3 (TT3), free T3 (FT3), total T4 (TT4), free T4 (FT4), and reverse T3 (rT3) were measured in 35 critically ill children admitted to intensive care unit (ICU) on days 1 and 3 of admission. Disease severity was evaluated using pediatric logistic organ dysfunction score (PELOD). Then the patients were divided into groups of survivors and non-survivors and the results were compared between these two groups accordingly. Results: Thirty-five patients, including 19 (54.3%) female and 16 (45.7%) male, with the mean age of 2 years (SD: ± 3.8 years, range: 4 months - 15 years) had entered the study based on the inclusion criteria. 25 (71.6%) patients were transferred from PICU to other wards and 10 (28.4%) patients died. Age and sex were not statistically different in survivors and non-survivors (P > 0.05). It was revealed that there was a significant reduction in mean TT3 levels in non-survivors compared to survivors on the first day of admission (P = 0.007). On the third day of admission, however, a significant reduction in TT4 levels were seen in non-survivors (P = 0.03). Conclusions: Thyroid function assessment, especially TT3 on the first day and TT4 on the third day of admission, along with PELOD score, might be helpful in predicting disease outcome and patient’s survival.