Summary Total circulating IgE levels were measured in a carefully selected normal population, using a highly sensitive double antibody assay. The mean level of 36.3 u/ml found in this group is much lower than that reported in all previous studies. No circadian rhythm was evident, but IgE levels varied slightly from day‐to‐day. IgE levels in 100 serum samples were compared using the double antibody assay and the Phadebas lest kit. based on a solid phase technique. A poor correlation was obtained with values below 100 u/ml, however, there was an excellent correlation for samples with IgE levels above this figure.
SYNOPSISThe stability of thyroxine and triiodothyronine in serum has been investigated. Apparent There has been a rapid increase in demand for hormone determinations during recent years (Landon et al, 1974). Such assays are often technically complex and many require the use of isotope counting equipment. Thus, at present, many laboratories send some samples to specialized analytical centres. This has the disadvantage that several days may elapse netween sample collection and assay, especially if there are postal delays or the sample arrives at the weekend. In addition, samples may be stored for several days at room temperature, sometimes unseparated or haemolysed, before despatch.Thyroid disorders are among the commonest endocrine abnormalities encountered in clinical practice and, for this reason, the stability of thyroxine (T4) and triiodothyronine (T3) has been studied in blood samples obtained and stored under a variety of conditions similar to those that might be encountered in normal clinical practice. The effect of sample storage in the light and in the dark has also been investigated. Materials and Methods PRELIMINARY INVESTIGATION OF THE STABILITY OF TOTAL T4 AND TOTAL T3Blood samples from each of six euthyroid subjects were divided into five aliquots, which were treated and stored for 48 hours under the conditions listed Received for publication 17 March 1975. 915 in the table. Total T3 levels were determined by radioimmunoassay, total T4 levels by a proteinbinding assay (Thyopac 4), and the capacity to bind labelled T3 was also assessed (THUT). COMPARISON OF THE EFFECT OF STORAGE ON APPARENT SERUM TOTAL T4 AND PROTEIN-BOUND IODINE LEVELSTwenty millilitres of blood from each of two euthyroid subjects was allowed to clot at room temperature and the serum was separated and stored at room temperature in the light. Samples of the serum were removed after 0, 3, and 6 days and stored at -20°C before measurement of proteinbound iodine and total T4 by the Thyopac 4 kit. COMPARISON OF THE EFFECT OF STORAGE ON APPARENT SERUM TOTAL T3 AND T4 LEVELS AS DETERMINED BY DIFFERENT METHODSBlood samples from three euthyroid subjects and from one clinically hyperthyroid patient were allowed to clot at room temperature, and the serum from each was divided into two aliquots, one of which was stored at room temperature and the other at 4°C. Samples were removed from each aliquot
A simple radioimmunoassay has been developed for service purposes to determine serum total thyroxine levels. Only three additions are required, of standard or sample, labelled thyroxine and antibody in polyethylene glycol. After 2 hours' incubation at room temperature the antibody-bound and free fractions are separated by centrifugation. Serum total thyroxine levels were measured in 195 euthyroid subjects and it was established that normal values lay within the range 57 to 155 nmol/1. Serial blood samples taken over a 24-hour period, from 11 subjects, indicated that there was no circadian rhythm so that samples for total thyroxine assay can be taken at any time of the day. Similar results were obtained using serum or plasma. Satisfactory results were obtained for three quality control sera when measured by seven different laboratories using this method.
The activity of many enzymes is elevated in primary hypothyroidism; creatine kinase, derived from muscle, is the activity most consistently elevated. The mechanism of this elevation is unknown. It has been postulated that, subsequent to high-energy phosphate depletion, there is increased permeability of the muscle cell membrane. Decreased ATP production due to thyroid hormone deficiency or increased consumption due to high concentrations of thyroid-stimulating hormone represent suggested mechanisms. In hypothermia, a frequent accompaniment of hypothyroidism, muscle creatine kinase activity is often raised. Thus we considered the possibility that the elevated creatine kinase activities in primary hypothyroidism are the consequence of hypothermia.We warmed 15 patients with primary hypothyroidism at rest in bed for 48 h. Five control patients were rested in bed for 48 h without being heated, after which they were rested for half an hour and exercised for half an hour, estimations of muscle creatine kinase activity and oral temperature being made after each test.In all warmed patients oral temperature rose (36.0 f 0.16OC to 36.9 f O.O9OC, P < 0.001) and creatine kinase activity fell (549.9 f 153.4to311.0 f 83.3i.u./l,P<0~01).Inthecontrol patients there was a small fall in muscle creatine kinase activity in response to rest (388.0 5 246.7 to 273.0 k 168.4) but thiswas not significant ( P > 0.2). In any case oral temperature actually rose in four of these patients during rest. There was only a small rise in the activity on exercising the controls, which was abolished by further rest.Our investigation shows that muscle creatine kinase serum activity in hypothyroidism falls in response to combined rest and heating. The rise in oral temperature of four of the control patients during bed rest highlights the problem of resting a patient in bed without imparting some heat. Nevertheless, the range variations in enzyme activity in response to short periods of exercise and rest was rather less than that seen in the warmed patients. Thus, in primary hypothyroidism, whilst exercise causes a definite elevation of muscle creatine kinase activity, hypothermia is probably a more important determinant of elevated activity of muscle creatine kinase. THE AUTOIMMUNE RESPONSE TO THYRO-GLOBULIN
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