Free thyroxine measurement by analogue immunoassay and equilibrium dialysis in dogs with non-thyroidal illness

Correlations of Free Thyroid Hormones Measured by Tandem Mass Spectrometry and Immunoassay in Dogs

Thyroid function is commonly assessed in dogs through serum measurements of free thyroxine (FT4) and thyroid-stimulating hormone (TSH). The accurate measurement of thyroid hormones is critical. In particular, the measurement of free thyroxine (FT4) is important for the diagnosis and management of thyroid disorders. Most laboratories measure FT4 using direct analog immunoassay methods. The reliability of the results obtained using these methods has often been questioned. Fifty-nine dogs for which the veterinarian had requested the evaluation of thyroid hormones were included in this study. FT4 and TSH were measured using chemiluminescence enzyme immunoassay (CLEIA). Furthermore, FT4 was also measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS) preceded by ultrafiltration. Comparing FT4 with the two different methods, the results demonstrate that LC-MS/MS, preceded by ultrafiltration, provides more accurate and specific FT4 measurements, particularly in dogs with altered thyroid hormone values. Although CLEIA is cost-effective and widely used for screening, LC-MS/MS is recommended for the more precise assessment of thyroid function.

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.

Alterations in serum concentrations of visfatin and betatrophin in dogs with hypothyroidism

BACKGROUND

Hypothyroidism in dogs is associated with obesity and altered lipid and carbohydrate metabolism. The adipokines, visfatin, and betatrophin, affect glucose tolerance. Betatrophin is involved in lipid regulation.

HYPOTHESIS

Visfatin and betatrophin serum concentrations are altered in hypothyroid dogs.

ANIMALS

Dogs with naturally occurring hypothyroidism (n = 25) and healthy dogs (n = 25).

METHODS

Insulin, visfatin, and betatrophin serum concentrations were measured in all dogs and 19 of the hypothyroid dogs after 30 days of thyroxine treatment. Body condition score (BCS) was determined (1-9 scale).

RESULTS

Visfatin concentrations were lower in hypothyroid compared with healthy dogs (mean, 95% confidence interval [CI]; 2.0 ng/mL, 1.2-3.3 vs 5.1 ng/mL, 3.3-7.8; P = .004) and increased post-treatment (3.1 ng/mL, 1.9-4.9 vs 2.6 ng/mL, 1.6-4.1; P = .05). Betatrophin concentrations were lower in lean to normal (body condition score [BCS], 3-5) hypothyroid dogs compared to lean to normal healthy dogs (52 pg/mL, 9-307 vs 597 pg/mL, 216-1648; P = .03), but were not different between overweight (BCS, 6-9) hypothyroid and healthy dogs (341 pg/L, 168-695 vs 178 pg/mL, 77-415; P = .26), and decreased post-treatment in overweight dogs (206 pg/mL, 87-488 vs 268 pg/mL, 112-640; P = .004). Visfatin concentrations were higher in overweight compared with lean to normal dogs (4.7 ng/mL, 3.3-6.6 vs 2.2 ng/mL, 1.2-4.2; P = .04). Betatrophin concentrations were positively correlated with BCS (r = .47, P = .02) and insulin concentrations (r = .48, P = .03) in hypothyroid dogs and negatively correlated with BCS (r = -.47, P = .02) and thyroid stimulating hormone concentrations (r = -.56, P = .01) in healthy dogs.

CONCLUSIONS AND CLINICAL IMPORTANCE

Hypothyroidism in dogs is associated with alterations in visfatin and betatrophin concentrations that partially resolve with thyroxine treatment.

Influence of medications on thyroid function in dogs: An update

Erroneous thyroid function test results can occur because of drugs that alter thyroid hormone physiology in one or more aspects, including synthesis, secretion, distribution, and metabolism. Research since publication of the last review in the Journal of Veterinary Internal Medicine (JVIM) 20 years ago has evaluated the effects of amiodarone, zonisamide, inhalant anesthetics, clomipramine, trilostane, and toceranib on thyroid function tests in the dog. In addition, recent work on the effects of glucocorticoids, sulfonamides, phenobarbital, and nonsteroidal anti-inflammatory drugs will be reviewed. Awareness of these effects is necessary to avoid misdiagnosis of hypothyroidism and unnecessary treatment.