Coagulation parameters in hyperthyroid cats before and after radioiodine treatment compared with healthy controls

Abstract

Objectives The aim of the study was to describe the coagulatory state of hyperthyroid cats before and after successful radioiodine therapy (RIT) compared with healthy age-matched controls, using classical coagulation parameters and thromboelastogram (TEG) as a global assessment method. The differences in coagulation activity after RIT, depending on the thyroid hormone (normal vs low total thyroxine [T4]) state, were also evaluated. Methods Fifteen hyperthyroid cats and 10 healthy age-matched controls were recruited. Hyperthyroid cats that remained hyperthyroid 14 days after RIT were excluded. Haematology, biochemistry, T4, prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen and TEG were assessed in control cats and hyperthyroid cats before and 7 and 14 days after RIT. Two weeks after successful RIT, further comparisons were made between cats with normal T4 vs those with low T4. Results Fourteen days after successful RIT, 7/15 cats had normal T4 and 8/15 had low T4. Thrombocytosis was noted in 6/15 cats after treatment. Fibrinogen was significantly higher ( P <0.001) and PT shorter ( P <0.01) in the hyperthyroid cats compared with the healthy controls and these changes persisted after RIT. Persistent increases in fibrinogen, PT, TEG maximal amplitude and TEG clot rigidity, reflecting clot stability, after RIT primarily occurred in the cats with normal T4. TEG-K (time until preset amplitude of 20 mm is reached) and alpha (α) angle reflected impaired fibrin cross-linking ability prior to RIT, which significantly increased after therapy ( P <0.05). Conclusions and relevance Based on some of the coagulation parameters, cats with hyperthyroidism showed hypercoagulable tendencies, which were mildly increased after RIT, possibly due to transient radiation-induced thyroiditis.

Evaluation of hemostasis in hyperthyroid cats

“…Along with AT, fibrinogen behaves as a positive acute phase protein in response to inflammatory cytokines (interleukin‐1, interleukin‐6, tumor necrosis factor alpha). In our study and in a previous study of hyperthyroid cats, plasma fibrinogen concentration was increased in agreement with findings in hyperthyroid humans 3,4,14 . In humans, vWF : Ag has been described as an acute phase reactant that strongly correlated with increases in serum C‐reactive protein concentration and normalized over time 19 .…”

“…This possibility is consistent with the existence of mechanisms other than cardiac disease that might be responsible for TE in hyperthyroid cats 5 . Hyperthyroid cats have been documented to have changes consistent with a hypercoagulable state as indicated by hyperfibrinogenemia and shortened PT, which might explain the occurrence of TE in affected cats that do not have clinically detectable thyrotoxic heart disease 14 …”

Thromboelastography in cats with cholestatic liver disease

“…It should be noted that hyperfibrinolysis has been noted in healthy control cats in some studies. 25,29,39 It is unclear if this represents true hyperfibrinolysis or occurs secondary to rapid clot retraction and separation from the test cup in this species. Cats are known to have hyperactive platelets, which might accelerate clot retraction speed.…”

“…26 The current study was carried out prior to a recent publication which recognized that cats with hyperthyroidism can be hypercoagulable and thus knowledge of thyroid status was not considered in the enrollment criteria. 29 Evaluation of coagulation in cats with CLD was limited to PT, aPTT, platelet count and TEG analysis and future studies should look at a broader range of coagulation parameters. It is possible that hyperfibrinolysis was missed in some cats.…”

“…14–19 In dogs with liver disease, TEG parameters consistent with hypercoagulable, hypocoagulable and hyperfibrinolytic states have been demonstrated. 20–22 TEG analysis has been performed in healthy cats, 23–25 cats with obesity, 26 acute trauma, 27,28 hyperthyroidism 29 and infection 30 and has been used to monitor feline anticoagulant therapy. 24,31 However, no studies have been conducted in cats with CLD.…”