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About 10% of hyperthyroid cats have a normal total T4 (TT4), requiring further testing to make the diagnosis. Thyroid stimulating hormone (TSH) is measured using the "canine" assay (TSH-CLIA, Immulite 2000 by Siemens) as the only assay currently available. However, this assay cannot differentiate between subnormal and low-normal TSH concentrations in cats due to poor specificity (70-85%). A novel feline-optimized TSH assay (TSH-BAW, Truforma by Zomedica) was recently developed. It allows differentiation between euthyroid and hyperthyroid cats. However, the effect of non-thyroidal illness (NTI) on TSH-BAW has not been evaluated. Our objectives included the comparison of serum TSH concentration using both the TSH-CLIA and TSH-BAW assays among hyperthyroid cats, cats with NTI, and healthy cats, and the evaluation of the sensitivity and specificity of the TSH-BAW for diagnosis of FHT. This prospective cross-sectional study was performed on 102 client-owned cats, including 37 hyperthyroid, 33 healthy, and 32 NTI cats. The following thyroid hormones were measured in all cats: TT4, TSH with both assays (Immulite 2000 and Truforma). Hyperthyroidism was confirmed by thyroid scintigraphy. Euthyroidism was confirmed by repeating TT4 measurement at least three months after enrollment (if available) to rule out subclinical hyperthyroidism. Cats with NTI were further divided based on the severity of their illness. Serum TSH was compared among groups using Kruskal-Wallis followed by Dunn's procedure, and compared among NTI severity scores using the Fisher's Exact test. Significance was set at P <0.05. The sensitivity and specificity of TSH-BAW for detecting hyperthyroidism are 78% (62-90%) and 97% (84-100%), respectively. The median TSH is significantly different between hyperthyroid cats and healthy and NTI cats with both assays (P<0.01). The TSH was not different between the latter euthyroid groups (P=0.87 and P=0.29). Eight (21.6%) hyperthyroid cats have a normal TSH-BAW but undetectable TSH-CLIA. Twelve (4 healthy, 8 NTI) euthyroid cats (18.5%) have an undetectable TSH-CLIA with only two (1 healthy, 1 NTI) (3%) having an undetectable TSH-BAW. The proportion of cats with a suppressed TSH is higher with severe illnesses with the TSH-CLIA only. In conclusion, the TSH-BAW has a high specificity, identifies normal TSH in healthy cats more often, and appears to not be affected by NTI. It can be a useful tool for the diagnosis of feline hyperthyroidism. However, a low-normal TSH cannot be used to rule out hyperthyroidism. / Master of Science / Hyperthyroidism leads to elevation of the thyroid hormone total T4 (TT4). About 10% of hyperthyroid cats have a normal TT4, requiring further testing to make the diagnosis. Another thyroid hormone, thyroid stimulating hormone (TSH), could be used like it is with people. In feline medicine, it is measured using the "canine" assay (TSH-CLIA, Immulite 2000 by Siemens) as the only assay currently available. However, this assay cannot differentiate between subnormal and low-normal TSH concentrations in cats due to poor specificity (70-85%). A novel feline-optimized TSH assay (TSH-BAW, Truforma by Zomedica) was recently developed. It allows differentiation between euthyroid and hyperthyroid cats. However, the effect of non-thyroidal illness (NTI) on TSH-BAW has not been evaluated. Our objectives included the comparison of serum TSH concentration using both the TSH-CLIA and TSH-BAW assays among hyperthyroid cats, cats with NTI, and healthy cats, and the evaluation of the sensitivity and specificity of the TSH-BAW for diagnosis of FHT. The study was performed on 102 client-owned cats, including 37 hyperthyroid, 33 healthy, and 32 NTI cats. The following thyroid hormones were measured in all cats: TT4, TSH with both assays (Immulite 2000 and Truforma). Cats with NTI were further divided based on the severity of their illness. Serum TSH was compared among groups using Kruskal-Wallis followed by Dunn's procedure, and compared among NTI severity scores using the Fisher's Exact test. Significance was set at P <0.05. The sensitivity and specificity of TSH-BAW are 78% and 97%, respectively. The median TSH is significantly different between hyperthyroid cats and healthy and NTI cats with both assays. The euthyroid cats (healthy and NTI cats) were not different. Eight (21.6%) hyperthyroid cats have a normal TSH-BAW (not normal in the face of hyperthyroidism) but undetectable TSH-CLIA. The proportion of euthyroid cats with a suppressed TSH (not normal in the face of euthyroidism) is higher with the TSH-CLIA compared to the TSH-BAW. Only with the TSH-CLIA, the proportion of NTI cats with a suppressed TSH is higher than healthy cats, and is higher with severe illnesses. In conclusion, the TSH-BAW has a high specificity, identifies normal TSH in healthy cats more often, and appears to not be affected by NTI. It can be a useful tool for the diagnosis of feline hyperthyroidism. However, a low-normal TSH cannot be used to rule out hyperthyroidism.

Background: Hyperthyroid cats are predisposed to thrombus formation. The mechanism for thrombogenesis is currently unknown, but could be associated with altered hemostasis as seen in hyperthyroid humans. Objective: The purpose of this study was to evaluate markers of hemostasis in hyperthyroid cats compared to healthy cats, and in hyperthyroid cats before and after treatments with radioactive iodine (RIT). Methods: Twenty-five cats with hyperthyroidism and 13 healthy euthyroid cats > 8 years of age were studied. Prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen, antithrombin (AT), D-dimers, thrombin-antithrombin complexes (TAT), von Willebrand Factor antigen (vWF:Ag), and activity of factors VIII and IX were measured. An echocardiogram was performed in all cats and healthy cats with abnormal echocardiograms were excluded. Measurements of hemostasis were evaluated again in 7 cats > 6 months after RIT and deemed to have restored euthyroid status. Results: There is a significant likelihood of being in hypercoagulable state based on hyperthyroid state (P = 0.019) and serum T4 level is significantly associated with predicating hypercoagulability (P = 0.043). Hyperthyroidism is associated with significantly higher median fibrinogen concentration (P < 0.0001), higher median AT activity (P < 0.0001), and higher median vWF:Ag level (P = 0.01) with all values decreasing significantly post-RIT. Fibrinogen and AT had a strong positive correlation with serum T4 value (r = 0.79; 95% CI 0.63 - 0.89 and r = 0.70; 95% CI 0.50 - 0.84, respectively). Presence of an abnormal echocardiogram in hyperthyroid cats was associated with a significantly higher median fibrinogen concentration (P = 0.03). Echocardiographic status did not have a significant impact on the remaining hemostatic markers in hyperthyroid cats. Conclusions: These results provide evidence of altered hemostasis and hypercoagulability in hyperthyroid cats that do not appear to be solely attributed to cardiac abnormalities. These differences of altered hemostasis resolved after radioiodine therapy, but further studies are warranted to determine if hypercoagulable state resolves. / Master of Science / In feline hyperthyroidism, there is a predisposition for thrombus formation. An alteration of hemostasis has been documented in hyperthyroid humans, but despite reports of thrombus formation in hyperthyroid cats, the underlying mechanism is currently unknown. Hyperthyroidism can lead to cardiac abnormalities that could possibly contribute thrombus formation, although thrombus formation has occurred in hyperthyroid cats without detected abnormalities. The goal of this study was to evaluate markers of hemostasis in hyperthyroid cats presenting for radioiodine therapy to evaluate for presence of hypercoagulability. Twenty-five hyperthyroid cats were evaluated with hemostasis panels and echocardiograms. The results were compared to a group of 13 healthy cats. Markers of hemostasis and echocardiograms in 7 hyperthyroid cats were also compared to results 6 months or greater post-radioiodine therapy. There was evidence of altered hemostasis and hypercoagulability in hyperthyroid cats. The alterations noted resolved after radioiodine therapy and do not appear to be solely attributed to cardiac abnormalities seen in hyperthyroid cats.