title: Serum transthyretin concentration is decreased in dogs with nonthyroidal illness.
abstract: BACKGROUND
  Hypothyroidism in dogs is often difficult to diagnose owing to nonspecific clinical signs and laboratory test results that can be mimicked by nonthyroidal illness (NTI). Thyroxine (T4) circulates in blood mainly bound to T4-binding globulin and, to a lesser degree, transthyretin (TTR) and albumin. The concentration of total T4 depends on the concentrations of these binding proteins.
  
  
  OBJECTIVE
  We hypothesized that dogs with NTI and decreased serum total T4 concentrations would have decreased serum TTR concentrations. The objective of the study was to measure and compare serum TTR concentrations in healthy dogs, in dogs with NTI and low serum T4 concentrations, and in dogs with hypothyroidism.
  
  
  METHODS
  Assignment of dogs to 3 groups was based on physical examination and serum concentrations of T4 and TSH (mean ± SD): for healthy dogs (n = 13), T4 was 24.8 ± 3.6 nmol/L and TSH was 0.15 ± 0.08 μg/L; for dogs with NTI and low T4 (n = 20), T4 was 3.2 ± 3.0 nmol/L and TSH was 0.18 ± 0.13 μg/L; and for hypothyroid dogs (n = 19), T4 was 5.3 ± 4.3 nmol/L and TSH was 2.33 ± 1.90 μg/L). TTR concentrations in serum were determined semiquantitatively using western blot analysis.
  
  
  RESULTS
  Serum TTR concentration (mean ± SD) was decreased in the dogs with NTI (24.8 ± 7.9 mg/L) compared with that of hypothyroid dogs (41.1 ± 21.4 mg/L, P = .0035). Differences were not found between TTR concentrations in clinically healthy dogs (33.3 ± 10.1 mg/L) and hypothyroid dogs or dogs with NTI.
  
  
  CONCLUSIONS
  Serum TTR concentrations were significantly decreased in dogs with NTI and low T4 compared with concentrations in hypothyroid dogs. Additional studies should be done to determine if TTR concentrations can discriminate between dogs with NTI and low T4 and dogs with primary hypothyroidism.
authors.affiliation: Clinic for Cattle, Endocrinology Laboratory, University of Veterinary Medicine Hannover, Hannover, Germany. marion.piechotta@tiho-hannover.de
authors.forename: Marion
authors.initials: M
authors.lastname: Piechotta
authors.forename: Raila
authors.initials: R
authors.lastname: Jens
authors.forename: Markus
authors.initials: M
authors.lastname: Rick
authors.forename: Martin
authors.initials: M
authors.lastname: Beyerbach
authors.forename: Hans-Otto
authors.initials: HO
authors.lastname: Hoppen
mesh_terms: D000818:Animals; D004283:Dog Diseases / Q000097:blood*; D004285:Dogs; D007037:Hypothyroidism / Q000097:blood / Q000662:veterinary*; D011228:Prealbumin / Q000378:metabolism*; D013974:Thyroxine / Q000097:blood / Q000378:metabolism
chemical_list: D011228:Prealbumin; D013974:Thyroxine