Assessment of in vitro thyroid function tests in 100 consecutive patients referred to a thyroid clinic

High serum thyroxine-binding globulin--an important cause of hyperthyroxinaemia

Four patients are described who had a significant elevation of serum thyroxine-binding globulin (TBG). Review of these patients indicated that inappropriate therapy for thyrotoxicosis had been given in three cases. A study of our laboratory records revealed that significant TBG elevation was a relatively common phenomenon which occurred in approximately 0.45% of our hospital population. Patients with this abnormality have serum thyroxine levels which are comparable to those with clinical thyrotoxicosis. Tri-iodothyronine is frequently elevated though less so than in patients with clinical thyrotoxicosis. Measurement of TBG is indicated in all cases of hyperthyroxinaemia in which the clinical features of thyrotoxicosis are doubtful. The TRH test was found to be most useful in evaluating the thyroid status of these patients.

Recovery of hypothalamic-pituitary-adrenal function after intermittent high-dose prednisolone and cytotoxic chemotherapy

Hypothalamic/pituitary and adrenal (HPA) function was assessed in ten patients who received intermittent high-dose prednisolone and cytotoxic chemotherapy for 5-40 months. Standard insulin hypoglycaemia (IHT), thyrotrophin-releasing hormone and tetracosactrin tests were performed 36 hr after the last dose of prednisolone and subsequently 10 days--52 weeks after completion of all chemotherapy. In the first tests there was evidence of impaired hypothalamic-pituitary function judged by peak adrenocorticotrophic hormone (ACTH), growth hormone (GH) and thyrotrophin (TSH) responses, and corresponding plasma corticosteroid responses were sub-normal in five patients. In the final IHTs, seven patients had persistently subnormal ACTH responses but all the corresponding plasma corticosteroid responses returned to normal. Mean peak corticosteroid responses to insulin and tetracosactrin and peak GH responses were significantly greater than in the first tests. Such chemotherapy regimens may have prolonged effects on hypothalamic/pituitary function but the demonstration of normal corticosteroid responses to hypoglycaemia and tetracosactrin indicates that these patients' stress responses will be normal as early as 10 days after treatment is stopped.

Simple solid-phase radioimmunoassays for total tri-iodothyronine and thyroxine in serum, and their clinical evaluation

1. Simple solid-phase radioimmunoassay methods for total tri-iodothyronine and thyroxine in serum or plasma are described. By using antibodies that are covalently coupled to microcrystalline cellulose, virtually identical assay procedures can be used for the determination of both hormones. An alkaline sodium glycinate buffer provides better assay conditions than the buffers often recommended for thyroid hormone radioimmunoassay. 2. Assay results are unaffected by moderate sample haemolysis. Plasma samples stored at room temperature for more than nine days often show an apparent increase in concentration of both thyroid hormones. 3. Serum tri-iodothyronine and thyroxine concentrations in healthy euthyroid subjects, and in euthyroid pregnant women are reported. In a series of 100 consecutive patients referred to a thyroid clinic the tri-iodothyronine assay discriminated better than the thyroxine assay between hyperthyroid and euthyroid patients. The thyroxine assay was much better than the tri-iodothyronine assay in discriminating between hypothyroid and euthyroid patients.

A strategy for thyroid function tests

The concept of decision-aiding ranges were introduced to improve diagnostic efficiency. The clinical uncertainty in distinguishing borderline cases of hyperthyroidism and hypothyroidism among 1559 consecutive requests for thyroid function tests was 47%. This was reduced to 22% by using the free thyroxine index and to under 2% by using specific tests determined by the decision-aiding ranges.

Thyroid status in the newborn infant. Effective thyroxine ratio and free thyroxine index

The effective thyroxine ratio (ETR) was determined in 28 term and 17 premature infants at birth and in 17 infants aged 0 to 6 weeks. The mean values found were significantly higher than those in 20 adult euthyroid controls. Serum thyroxine (T₄), T₃ resin uptake ratio (T₃ RUR), free thyroxine index (FTI), and ETR were determined in 14 term infants at birth. It was concluded that the raised T₄ was partly due to an increase in thyroxine binding globulin but that there was also a degree of true thyroid hyperactivity. Serum thyroxine alone was not considered a suitable index of thyroid function in infants and the free thyroxine index or the effective thyroxine ratio was preferred instead.