Criteria of the test of suppression of thyroid uptake of I131 by triiodothyronine]

The author assessed the results of the test of the triiodothyronine (T3) suppression of the I131 absorption in 10 healthy women, 22 suffering from neurocirculatory dystrophy and 35 patients with diffuse toxic goiter. This test was found to distinctly differentiate the patients with diffuse toxic goiter and healthy persons. Reduction of absorption to the level below 15% of the indicator dose with consideration to the level of the initial absorption could be considered as criterion of the normal I131 absorption in response to the T3 administration. The mean suppression of the absorption in T3 administration in patients with neurocirculatory dystonia (10.7 +/- 1.49%) displayed a significant difference from the level of mean suppression of the absorption in patients with diffuse toxic goiter (58.1 +/- 4.76%). However, in individual patients suffering from neurocirculatory dystonia the I131 absorption by the thyroid gland in T3 administration still exceeded such in healthy persons. Therefore such patients require further observation because of a possible development in them of diffuse toxic goiter.     

Relation of TRH test to thyroidal suppression test by triiodothyronine in patients with hyperthyroidism under treatment with antithyroid drugs (author's transl)]

The relation of the TRH test to the T3 suppression test was investigated in 43 patients with hyperthyroidism receiving antithyroid drugs for 6 to 27 months (average 14 months). TRH tests were performed by measuring serum TSH levels before and 15, 30, 45, 60, 90 and 120 minutes after intravenous injection of 500 mug of synthetic TRH. Serum TSH was measured by a double antibody radioimmunoassay. Two weeks later, the T3 suppression test was performed by measuring the 24-hr thyroidal uptake of radioiodine after daily administrations of 75 mug of triiodothyronine for 8 days. All patients under study were in euthyroid state, estimated by serum T3-RSU, T4, T3 and FT4I. The value for 24-h uptake after T3 administration was less than 20% in 18 cases, out of which the response to TRH was normal or exaggerated in 15 cases and was absent or impaired in 3 cases. On the other hand, out of 25 cases with the value of 24-h uptake more than 20%, the response to TRH was absent or impaired in 18 cases and was normal or exaggerated in 7 cases. The results of the TRH test and the T3 suppression test were correlated in 33 out of 43 cases. The responsiveness to TRH and the suppressibility with T3 was dissociated in 10 cases, suggesting the TRH test could not replace the T3 suppression test.     

The deoxyuridine suppression test in peripheral lymphocytes

The effects of different deoxyuridine (dU) concentrations on lymphocytes stimulated with phytohemagglutinin (PHA) were studied for use in a lymphocyte dU suppression test (L-dUST). High concentrations of dU were necessary to overcome the unspecific spontaneous pattern of folate deficiency, dU suppression tests with cells of bone marrow (BM-dUST) and with lymphocytes were carried out in 15 patients with vitamin B-12 deficiency, in 12 with folate deficiency, and in 10 with other pathological conditions. L-dUST was also carried out in 15 healthy reference controls. The BM-dUST was able to distinguish patients with vitamin B-12 or folate acid deficiencies from those without, while the L-dUST was unable to do so in most cases. L-dUST does not, therefore, appear to be a reliable method for the diagnosis of megaloblastic changes.     

Is conversion of thyroxine to triiodothyronine and reverse triiodothyronine autoregulated? Studies with short term suppression of thyroid function with 3'isopropyl 3,5-diiodothyronine

We investigated the effect of a 6 days course of 20 micrograms of a thyromimetic thyronine analogue 3'isopropyl, 3,5-diiodothyronine (DIIP) on serum thyroid hormone and TSH levels in 10 normal male volunteers. TSH was inhibited progressively during the 6 days of DIIP treatment. By the third day after stopping the treatment this trend had already reversed. Of the serum thyroid hormones the T3 level had decreased by 32% and was the first to increase 5 days after stopping treatment. Serum T4 fell by 35% and returned later to normal. The next effect was an increase in the T3/T4 ratio which was most marked 5 days after treatment had stopped. Kinetic studies with 125I-T3 and 125I-reverse T3 were performed at this time. In comparison to pretreatment kinetics no change in MCR was obtained. It is therefore suggested that at least part of the more rapid increase of T3 than T4 after stopping the suppression therapy reflects an increased conversion.     

The dexamethasone suppression test and depression. Approaches to the use of a laboratory test in psychiatry

The dexamethasone suppression test has undergone unprecedented study among the biologic tests proposed for clinical use in psychiatry. Since the 1970s, its study has involved hundreds of reports and thousands of patients. Although important technical aspects of the test appear to be well accepted and validated, additional information is needed regarding the pharmacokinetics of dexamethasone. Marked interindividual differences in plasma dexamethasone suggest that performance of the test might be improved by factoring dexamethasone levels into test interpretations. There also may be advantages to the development of a modified test involving other exogenous and index steroids, such as monitoring corticosterone levels. Although it is too early to determine how ROC analysis will alter the clinical application of the test, some implications for methodology and data presentation are already clear. First, because the test is a diagnostic system with nonbinary outcomes, ROC analysis can augment traditional performance indices such as sensitivity, specificity, and positive predictive power. Second, ROC analysis will improve comparisons between the studies of different research groups and will help assess innovations in the application of the test. Third, ROC analytic techniques permit appropriate planning of sample size given estimates of the expected values of AUC that would be obtained from the studies. ROC theory thus promises to play an increasingly important role in the evaluation and future improvement of the dexamethasone suppression test and other biologic markers in clinical psychiatry. In conclusion, neither uncritical enthusiasm nor excessive skepticism is warranted about the use of the dexamethasone suppression test in clinical psychiatry. Evidence to date should encourage investigators to pursue refinement of the test or other tests of hypothalemic-pituitary-adrenal functioning to increase their accuracy and clinical utility.     

The ovine corticotropin-releasing hormone stimulation test and the dexamethasone suppression test in the differential diagnosis of Cushing's syndrome

We gave a standard dexamethasone suppression test and an ovine corticotropin-releasing hormone (CRH) stimulation test to 41 patients with adrenocorticotrophic hormone (ACTH)-dependent hypercortisolism to determine the efficacy of each test in the differential diagnosis of Cushing's syndrome. Twenty-nine of thirty-three patients with Cushing's disease and 0 of 8 patients with ectopic secretion of ACTH responded to the ovine CRH test with increased levels of cortisol. When a cortisol response was judged as positive for Cushing's disease, the CRH test had a diagnostic sensitivity, specificity, and accuracy of 88%, 100%, and 90%, respectively. Twenty-nine patients with Cushing's disease and 1 patient with ectopic secretion of ACTH responded to the dexamethasone suppression test. A combined-test strategy requiring negative results from both tests to exclude a diagnosis of Cushing's disease yielded superior sensitivity (100%) and diagnostic accuracy (98%). Thus, the ovine CRH test works as well as the standard dexamethasone suppression test in discriminating between Cushing's disease and ectopic ACTH secretion. The diagnostic power of each test is enhanced when the two tests are combined.