Recent advances in routine thyroid function testing

Equine thyroid function tests: a preliminary investigation

A similar and significant (P less than 0.001) increase in plasma thyroxine (T4) concentration was seen in seven clinically normal thoroughbred horses 2 h after the intravenous administration of either 2.5 iu or 5 iu of thyroid stimulating hormone (TSH) with a peak response around 4 h after administration. The intravenous administration of 0.2, 0.5 or 1 mg thyrotrophin releasing hormone (TRH) resulted in a significant (P less than 0.01) increase in T4 concentration in three groups of animals; six thoroughbreds in full work, five thoroughbreds at rest and four ponies at rest. The peak response was recorded at 3 or 4 h after administration. A significant difference between the groups in the degree of response to TRH was only found between the thoroughbreds in work and those at rest with 1 mg TRH (P less than 0.05). When two additional ponies were investigated in a similar way, a reduced response to TRH was observed: a pregnant mare had a similar response to 5 iu TSH as the thoroughbreds; the other pony also showed a lowered response to TSH. In a group of 2- or 3-year-old thoroughbreds in training no difference in the T4 response 4 h after intravenous administration of 0.5 mg TRH could be determined, according to the month, age, sex or work intensity. Although resting T4 concentrations did not differ significantly between animals believed to be suffering from the equine rhabdomyolysis syndrome (ERS) and those suffering from a variety of other conditions, some ERS sufferers may have a lowered response to TRH.

Effective laboratory evaluation of thyroid status

This article focuses on recent developments in thyroid-related laboratory tests, including analytical methods, clinical utility, and limitations of TSH, FT4, T4, FT3/T3, thyroglobulin, and thyroid autoantibodies and the effective use of these tests in the diagnosis of various forms of hypothyroidism or hyperthyroidism, and the management of patients undergoing T4 replacement, T4 suppression, or antithyroid drug therapy.