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. 2024 Jan-Feb;38(1):111-122.
doi: 10.1111/jvim.16947. Epub 2023 Nov 30.

Thyroid function tests during nonthyroidal illness syndrome and recovery in acutely ill dogs

Timothy A Bolton  1 , David L Panciera  1 , Caylie D Voudren  1 , Matthew I Crawford-Jennings  1
Affiliations

Thyroid function tests during nonthyroidal illness syndrome and recovery in acutely ill dogs

Timothy A Bolton et al. J Vet Intern Med. 2024 Jan-Feb.

Abstract

Background: Nonthyroidal illness syndrome (NTIS) can result in thyroid function test alterations that mimic hypothyroidism. The duration of NTIS-induced changes in dogs is not well-described.

Objectives: Document alterations in thyroid function tests during NTIS and recovery, and the time necessary for their resolution.

Animals: From 103 dogs sampled, 25 euthyroid dogs with acute, resolvable illness having a low serum total thyroxine (TT4) concentration on admission were analyzed.

Methods: Prospective observational study. Serum TT4 concentration was measured in 103 dogs within 4 hours of admission. If below the reference interval (RI), subsequent serum samples were obtained every 24 hours from admission until discharge (acute phase) and at 2 weeks and 4 weeks after discharge (recovery phase). Serum samples were submitted for batch measurement of serum TT4, free thyroxine (fT4), total 3,5,3'-triiodothyronine (TT3), and thyroid-stimulating hormone (TSH) concentrations.

Results: In the cohort of dogs analyzed, serum TT4, TT3, and fT4 concentrations were below the RI in 100%, 80%, and 16% at admission; 20%, 80%, and 0% at discharge; 4%, 8%, and 0% at 2 weeks; and 0%, 0%, and 0% at 4 weeks, respectively. Serum TSH concentration was within the RI in 100% at admission and discharge, and above the RI in 4% and 12% at 2 weeks and 4 weeks, respectively.

Conclusions and clinical importance: Naturally occurring NTIS in dogs induces alterations in thyroid function tests during acute illness and recovery. Measurement of serum TT4 concentration 2 to 4 weeks after discharge or serum fT4 concentration by ED during illness is recommended for accurate assessment of thyroid function in acutely ill dogs.

Keywords: dog; hypothyroidism; normalization; sick.

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Conflict of interest statement

Authors declare no conflict of interest.

Figures

FIGURE 1
FIGURE 1
Box‐and‐Whisker plots of the serum total thyroxine (TT4) concentrations (nmol/L) at the 4 major study time points. The shaded area indicates the reference interval.
FIGURE 2
FIGURE 2
Box‐and‐Whisker plots of the serum total triiodothyronine (TT3) concentrations (nmol/L) at the 4 major study time points. The shaded area indicates the reference interval.
FIGURE 3
FIGURE 3
Box‐and‐Whisker plots of the serum free thyroxine (fT4) concentrations (pmol/L) at the 4 major study time points. The shaded area indicates the reference interval.
FIGURE 4
FIGURE 4
Box‐and‐Whisker plots of the serum thyroid‐stimulating hormone (TSH) concentrations (ng/mL) at the 4 major study time points. The shaded area indicates the reference interval.
FIGURE 5
FIGURE 5
Box‐and‐Whisker plots of the TT3/TT4 ratios at the 4 major study time points.
FIGURE 6
FIGURE 6
Box‐and‐Whisker plots of the fT4/TT4 ratios at the 4 major study time points.
FIGURE 7
FIGURE 7
Box‐and‐Whisker plots of the TT4/TSH ratios at the 4 major study time points.
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