Evaluation of the thyroid status of Basenji dogs in Australia

[Impact of hypothyroidism on bitch fertility and neonatal mortality and morbidity - a review of the literature]

There are a few studies and case reports that postulate a connection between hypothyroidism and reproductive disorders in bitches and an increased neonatal mortality and morbidity in puppies. Other studies, however, cannot demonstrate a connection between hypothyroidism and reproductive disorders in bitches. In this work, the relevant literature is to be checked for its evidence. The connection between hypothyroidism and reproductive disorders in the bitch, puppy mortality and neonatal morbidity to hypothyroidism will be analyzed based on a literature review. For this purpose, the available German and international "English-language" literature from 1986 to January 2023 was analyzed. It turns out that only a small amount of literature contains high levels of scientific evidence, as it mostly consists of case reports and expert opinions. In some case reports a connection between estrous abnormalities, galactorrhoea and infertility and the presence of hypothyroidism could be seen, but in experimental studies and according to the opinion of other authors the connection between hypothyroidism and reproductive disorders does not exist. A negative influence of hypothyroidism on the birth process could not be clearly proven. In an experimental study, although the duration and intensity of uterine contractions were longer and weaker in animals with hypothyroidism, the interval between pup births was not affected. Only in the area of neonatal mortality and morbidity a connection with the hypothyroidism of the dam could be demonstrated. The puppies of affected bitches showed a lower birth weight and were weaker than puppies of euthyroid bitches. The importance of hypothyroidism for fertility in the bitch has not yet been documented in the literature, but this endocrinopathy seems to have an influence on neonatal vitality.

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

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.

Relationship between thyroid function and sex hormones in female German shepherd dogs

BACKGROUND

Several variables influence the serum concentration of thyroid hormones in dogs, including breed, age, drugs, and concurrent diseases. However, data regarding the interaction between thyroid function and the estrous stage of female dogs are limited.

HYPOTHESIS

Estrous stage may influence thyroid function in German Shepherd dogs.

METHODS

Longitudinal, observational, non-randomized cohort study. The dogs were monitored during the complete estrous cycle, and different stages were determined by vaginal cytology. Two blood samples were collected at the beginning and end of each stage to analyze the following: total thyroxine (TT4), free thyroxine (fT4), total triiodothyronine (TT3), free triiodothyronine (fT3), canine thyrotropin (cTSH), progesterone, 17-β-estradiol, triglycerides, and cholesterol concentrations. Hematological and biochemical evaluations were performed at the beginning and end of the study period.

ANIMALS

Seventeen German Shepherds were included, of which 7 were bred during the study period. One dog was excluded for estrus interruption and another for suspected hypothyroidism.

RESULTS

Serum concentrations of T4, fT4, and fT3 were negatively correlated with age. Total thyroxine demonstrated significant changes in serum concentrations between estrous stages, with higher concentrations in estrus and diestrus. Total thyroxine concentrations were positively correlated with progesterone concentrations and negatively correlated with 17-β-estradiol concentrations. Free thyroxine did not show significant variations but was positively correlated with progesterone concentrations. Canine TSH concentrations were positively correlated with 17-β-estradiol concentrations. No significant differences in thyroid hormones and cTSH concentrations were observed between diestrus during pregnancy and pseudopregnancy.

CONCLUSIONS

Different stages of estrus can influence the measurement of TT4 in female dogs.

Development and internal validation of diagnostic prediction models using machine-learning algorithms in dogs with hypothyroidism

Introduction

Hypothyroidism can be easily misdiagnosed in dogs, and prediction models can support clinical decision-making, avoiding unnecessary testing and treatment. The aim of this study is to develop and internally validate diagnostic prediction models for hypothyroidism in dogs by applying machine-learning algorithms.

Methods

A single-institutional cross-sectional study was designed searching the electronic database of a Veterinary Teaching Hospital for dogs tested for hypothyroidism. Hypothyroidism was diagnosed based on suggestive clinical signs and thyroid function tests. Dogs were excluded if medical records were incomplete or a definitive diagnosis was lacking. Predictors identified after data processing were dermatological signs, alopecia, lethargy, hematocrit, serum concentrations of cholesterol, creatinine, total thyroxine (tT4), and thyrotropin (cTSH). Four models were created by combining clinical signs and clinicopathological variables expressed as quantitative (models 1 and 2) and qualitative variables (models 3 and 4). Models 2 and 4 included tT4 and cTSH, models 1 and 3 did not. Six different algorithms were applied to each model. Internal validation was performed using a 10-fold cross-validation. Apparent performance was evaluated by calculating the area under the receiver operating characteristic curve (AUROC).

Results

Eighty-two hypothyroid and 233 euthyroid client-owned dogs were included. The best performing algorithms were naive Bayes in model 1 (AUROC = 0.85; 95% confidence interval [CI] = 0.83-0.86) and in model 2 (AUROC = 0.98; 95% CI = 0.97-0.99), logistic regression in model 3 (AUROC = 0.88; 95% CI = 0.86-0.89), and random forest in model 4 (AUROC = 0.99; 95% CI = 0.98-0.99). Positive predictive value was 0.76, 0.84, 0.93, and 0.97 in model 1, 2, 3, and 4, respectively. Negative predictive value was 0.89, 0.89, 0.99, and 0.99 in model 1, 2, 3, and 4, respectively.

Discussion

Machine learning-based prediction models were accurate in predicting and quantifying the likelihood of hypothyroidism in dogs based on internal validation performed in a single-institution, but external validation is required to support the clinical applicability of these models.

Biological variation of total thyroxine (T4), free T4 and thyroid-stimulating hormone in 11 clinically healthy cats

OBJECTIVES

The aim of this study was to investigate the biological variation of total thyroxine (T4), free T4 (fT4) and thyroid-stimulating hormone (TSH) in 11 clinically healthy cats aged between 3 and 15 years old, in Sydney, Australia.

METHODS

Blood was collected weekly for up to 6 weeks and serum T4, fT4 and TSH concentrations were analysed using canine-specific reagents. Restricted maximum likelihood was used to estimate within-subject, between-subject and analytical variance components, which were recorded in terms of the related coefficients of variation. The index of individuality and reference change values were then calculated for each analyte.

RESULTS

T4 and TSH had intermediate individuality, indicating both subject-based and population-based reference intervals (RIs) could be used, with the knowledge that population-based RIs are suboptimally sensitive. fT4 had high individuality, indicating subject-based RIs are more appropriate than population-based RIs.

CONCLUSIONS AND RELEVANCE

This study has demonstrated that subject-based RIs could be more sensitive than population-based RIs for the diagnosis of thyroid dysfunction in cats.

Recombinant human thyrotropin stimulation test in 114 dogs with suspected hypothyroidism: a cross-sectional study

OBJECTIVE

To evaluate the performance and define cut-offs for the interpretation of a thyroid-stimulating hormone (TSH) stimulation test with a recombinant human TSH dose of 75 μg/dog administered intravenously in dogs with suspected hypothyroidism.

MATERIALS AND METHODS

Cross-sectional study. Medical records of dogs presented for suspected hypothyroidism were retrospectively reviewed. Animals were included if a TSH stimulation test with a recombinant human TSH dose of 75 μg/dog was performed and follow-up was available. Dogs with a post-TSH serum total thyroxine (T4) level of ≥2.2 μg/dL were considered euthyroid. Dogs with a post-TSH T4 level of <2.2 μg/dL were classified as hypothyroid or euthyroid based on follow-up, including response to levothyroxine supplementation. A receiver operating characteristic curve analysis was used to define the performance of the test.

RESULTS

One hundred and fourteen dogs were included. Forty were classified as hypothyroid and 74 as euthyroid. Post-TSH T4 cut-offs of 1.3 and 1.7 μg/dL showed sensitivities of 92.5 and 100% and specificities of 97.3 and 93.2%, respectively. Post-TSH T4 levels of >1.7 μg/dL had a negative predictive value of 100%. Post-TSH T4 levels of <1.3 μg/dL showed a positive predictive value of 94.9%. Area under the ROC curve for post-TSH T4 was 0.99.

CLINICAL SIGNIFICANCE

A TSH stimulation test performed with a recombinant human TSH dose of 75 μg/dog is highly reliable to discriminate between hypothyroid and euthyroid dogs, even in cases of concurrent non-thyroidal illness or administration of medications. A post-stimulation T4 concentration of >1.7 μg/dL is suggestive of normal thyroid function.

Risk factors for low plasma thyroxine and high plasma thyroid-stimulating hormone concentrations in dogs with non-thyroidal diseases

The aim of the current study was to identify independent risk factors for thyroid axis alterations in dogs with non-thyroidal diseases. In this retrospective cross-sectional study, data and plasma samples from 207 dogs with non-thyroidal diseases was used. The involvement of various factors (disease severity, sex, age, breed, category and duration of disease, and medication) in the alteration of plasma thyroxine (T4) or thyroid-stimulation hormone (TSH) concentrations was analyzed using multivariate logistic regression. Among the 207 dogs analyzed, 99 (47.8%) had low plasma T4 concentrations, while 45 (21.7%) had high TSH concentrations. Intact male sex [odds ratio (OR), 3.25; 1.67-6.35; P<0.001], Labrador Retrievers (OR, 18.70; 2.32-151.00; P=0.006), moderate (OR, 2.39; 1.21-4.74; P=0.012) and severe diseases (OR, 6.84; 2.27-20.70; P<0.001) were associated with increased risk for low plasma T4 concentrations. Meanwhile, intact male (OR, 3.93; 1.51-10.30; P=0.005), spayed female (OR, 4.22; 1.59-11.20; P=0.004), older age (OR, 2.73; 1.28-5.84; P=0.009), and Miniature Dachshunds (OR, 5.39; 2.38-12.20; P<0.001) had increased risk for high plasma TSH concentrations. Disease severity had been determined as an independent risk factor for canine NTIS. In addition, sex, age and breed were also associated with thyroid axis alterations in dogs with non-thyroidal diseases.

Breed-specific reference intervals for assessing thyroid function in seven dog breeds

Thyroxine (T4), free T4 (FT4), and thyrotropin (TSH) concentrations were measured in serum from 693 healthy representatives from 7 dog breeds (Alaskan Malamute, Collie, English Setter, Golden Retriever, Keeshond, Samoyed, or Siberian Husky) to determine whether breed-specific reference intervals (RIs) are warranted. Veterinarians reviewed the health history, performed a physical examination, and approved laboratory data for the enrolled dogs. Many purebred dogs had T4 and FT4 concentrations that were at, or below, the lower limits previously determined for non–breed-specific RIs. Mean concentrations of T4, FT4, and TSH varied significantly among breeds. The range of mean concentration of T4 (19.7 nmol/L [1.53 µg/dL] in English Setters to 29.0 nmol/L [2.25 µg/dL] in Keeshonds) and FT4 (12.6 pmol/L [0.98 ng/dL] in English Setters to 20.2 pmol/L [1.57 ng/dL] in Samoyeds) was considerable. Median TSH values ranged from 6.10 mIU/L (0.07 ng/mL; Alaskan Malamute and Golden Retriever) to 17.6 mIU/L (0.26 ng/mL; Collie). Mean T4 and FT4 concentrations were higher in females. Increasing age was associated with decreasing T4 and FT4, and increasing TSH concentration. The substantial ranges across breeds of measures of central tendency (mean, median) for all hormones indicate that breed-specific RIs are warranted. RIs encompassing the central 95% of reference values for all breeds combined, and for individual breeds, were calculated using nonparametric (TSH) and robust (T4, FT4) methods. Use of breed-specific RIs in combination with careful attention to the potential for pre-analytical and analytical variability in test results will improve thyroid function assessment in these breeds.

Seasonal influence on the thyroid gland in healthy dogs of various breeds in different weights

The aim of our study was to evaluate the influence of seasonal ambient temperature on the thyroid gland function in terms of serum total thyroxine (TT4), free thyroxine (fT4), total triiodothyronine (TT3), and canine thyroid stimulating hormone (cTSH) concentrations in healthy dogs of various breeds living outdoors and to compare them with those living indoors in flats and houses. The monitoring was conducted for 5 years and our study included 162 indoor dogs and 148 outdoor dogs of both sexes from 2 to 12 years of age, categorised into 3 groups according to their body weight: large (n = 17), medium (n = 16) and small (n = 17) breeds. Comparison of the seasonal serum TT4 and fT4 concentrations in both the indoor and outdoor dogs confirmed their fluctuation in relation to the ambient temperature in all weight groups with the lowest average of TT4 and fT4 concentrations recorded in summer and the highest ones in winter. In dogs kept outdoors, the fluctuation of hormone values was significant (P < 0.05). Seasonal serum cTSH fluctuation was found to be significant (P < 0.05) only in the medium breeds living outdoors, but their concentrations did not exceed the reference ranges. The 5-year monitoring of serum TT3 in indoor and outdoor dogs of large, medium, and small breeds clearly showed that its concentrations were not influenced by varying ambient temperature. The study provides for the first time evidence that serum TT4 and fT4 concentrations in dogs kept outdoors directly depend on ambient temperature. This correlation was also expressed by mathematical equations.