Evaluation of Canine Serum Thyrotropin (TSH) Concentration: Comparison of Three Analytical Procedures

Abstract

Abstract.A comparative study of 3 analytical methods (immunoradiometric assay, enzyme immunometric assay, and chemiluminescent immunometric assay) for canine serum thyrotropin (TSH) was performed. Ninetysix dogs were included in the study. The within-and between-run precision was evaluated for each method, and correlations for the results obtained with each method were examined. The best within-and between-run precision was obtained with the chemiluminescent immunometric assay. Satisfactory correlations for the 3 analytical procedures were obtained but varied in relation to serum TSH concentration.Hypothyroidism is a common endocrinopathy in the dog. The diagnosis is based on the presence of typical clinical signs, results of thyroid function tests, and response to specific replacement therapy. The clinical signs are variable and nonspecific. 5 Thyroid function tests may be affected by many nonthyroidal factors or diseases. 1 Even response to therapy can be difficult to evaluate, particularly when other concurrent treatments have been instituted with thyroid hormone supplementation.Measurement of basal serum total thyroxine (TT4) has been frequently used in the evaluation of thyroid function, but the diagnostic value of a single low basal TT4 level has not been considered very useful. 8,9,11 For this reason, stimulation tests using thyroid-stimulating hormone (TSH, Thyrotropin) or thyroid-releasing hormone have been proposed. 4,7 Recently, an assay to measure canine TSH has been developed. Serum TSH is the most accurate test of thyroid function in humans. 12 Unfortunately, assay performance in the dog has been disappointing, and initial results have not been reliable when the measurement of canine TSH is the only assay performed. 3,6,8,10 However, further studies should be implemented, and most of the researchers agree that the assay could be helpful in the evaluation of hypothyroid dogs. 3,7,9,11,13 Three procedures can be used in the analysis of canine TSH: immunoradiometric assay, enzyme immunometric assay, and chemiluminescent immunometric assay. Most of the results published to date have been obtained with the immunoradiometric assay, and very little information about the other two methods is available. The aim of this study was to evaluate the analytical precision of the 3 methods and to compare the results obtained with each assay. Material and methodsAnimals. Blood samples were obtained from 96 dogs of different ages, sexes, and breeds from the Small Animal Internal Medicine Department at the Veterinary Faculty of the University of Zaragoza (Spain). Fasting blood samples were collected from the jugular vein of each dog into plain tubes. After coagulation, the samples were centrifuged (3,000 rpm for 10 min), and aliquots were stored at Ϫ20 C until analysis. The samples were stored for a maximum of 2 mo. Canine TSH has been shown to be stable for this period. 13 Analytical procedures. Serum canine TSH was evaluated in each sample by 3 commercially available methods. The manufacturers' instructions were fol...

Hypothyroidism

“…The alpha subunit is identical to that of the alpha subunit of the related glycoprotein hormones LH, FSH, and chorionic gonadotrophin, whereas the beta subunit is unique to TSH and confers the biologic properties of TSH. The assay used most commonly is the chemiluminescent TSH assay (Immulite Canine TSH), which has been demonstrated to have the highest precision compared to immunoradiometric and enzyme immunometric methods (Marca et al, 2001). The first assay for canine TSH was validated in 1996 (Williams et al, 1996), and since that time there have been other commercial assays developed.…”

Keratoconjunctivitis sicca attributable to parasympathetic facial nerve dysfunction associated with hypothyroidism in a horse

“…In 18% to 38% of dogs with hypothyroidism, serum TSH measurements are within reference range, and as many as 14% of euthyroid dogs have increased serum TSH concentrations. 36 In healthy horses, baseline serum concentrations of TSH vary greatly, but assessments of this variable may be useful in the diagnosis of hypothyroidism once reference values become available. 15,32 Ultrasonographically, the thyroid gland lobes of hypothyroid dogs are typically reduced in size and volume and the thyroid parenchyma has decreased echogenicity, compared with findings in clinically normal dogs.…”

Behavior in dogs with spontaneous hypothyroidism during treatment with levothyroxine

“…Frozen serum aliquots were used for measurement of TT4, TSH, and serotonin. Serum TT4 and TSH concentrations were determined using a previously validated commercially available solid‐phase, chemiluminescent competitive immunoassay (Immulite 2000 Canine TSH and Total T4; Gwynedd, United Kingdom) . Frozen heparinized samples used for the measurement of PRL were transported for analysis to Utrecht University on dry ice.…”