Retrospective evaluation of circulating thyroid hormones in critically ill dogs with systemic inflammatory response syndrome

Abstract

Critical illness can be associated with transient alterations in circulating thyroid hormone concentrations, indicating the presence of non-thyroidal illness (NTI). NTI is well described in humans, but there are few reports on its occurrence and prognostic significance in dogs. This retrospective study assessed the occurrence of NTI in a population of dogs with systemic inflammatory response syndrome (SIRS) and investigated its association with disease severity (APPLE_fast scores). A total of 41 SIRS dogs were included and were divided by SIRS origin (non-septic SIRS, n = 10; septic SIRS, n = 41) and final outcome (survivors, n = 37; non-survivors, n = 4). Healthy, age-matched dogs (n = 15) were included as controls. Serum thyroid hormone levels including total T3, free T3, total T4, and reverse T3 were measured upon admission. Compared to controls, there were significant changes in serum thyroid hormone concentrations in SIRS dogs, suggesting the presence of NTI. Septic SIRS dogs had higher APPLE_fast scores and lower serum thyroid hormones concentrations than those in non-septic SIRS and control dogs. In conclusion, NTI was frequent in dogs with SIRS and may be associated with the presence of sepsis or high illness severity.

Keywords: canine; euthyroid sick syndrome; systemic inflammatory response syndrome; thyroid hormones.

Fig. 1. Box plots of serum total triiodothyronine (TT3) concentrations among dogs with non-septic systemic inflammatory response syndrome (SIRS), dogs with septic SIRS, and control dogs; the central box represents the values from the lower to upper quartile (25 to 75 percentile). The middle line represents the median. The vertical line extends from the minimum to the maximum value, excluding outside and far out values which are displayed as down-pointing triangles. Asterisk indicates significant (p < 0.05) differences among groups.

Fig. 2. Box plots of serum total thyroxine (TT4) concentrations among dogs with non-septic systemic inflammatory response syndrome (SIRS), dogs with septic SIRS, and control dogs; the central box represents the values from the lower to upper quartile (25 to 75 percentile). The middle line represents the median. The vertical line extends from the minimum to the maximum value, excluding outside and far out values which are displayed as open circles. Asterisk indicates significant (p < 0.05) difference from septic SIRS.