Comparison between serum thyroxine and triiodothyronine estimation and the TRH test in the routine diagnosis of hyperthyroidism

T4, T3 and reverse-T3 determinations in connection with the TRH test in the evaluation of possible hyperthyroidism

One disadvantage of the TRH test is that an absent or blunted TSH response is seen not only in hyperthyroid patients but also in some normal subjects. The aim of the present study was to elucidate whether the discriminatory power between eu- and hyperthyroidism could be increased by determining the T3 and T4 levels before and after the TRH administration. The study population consists of 30 patients referred for evaluation of suspected hyperthyroidism. The results show that all but one of the patients (n=20) who had T3 levels within the normal reference limits increased these levels after TRH administration, whether their TSH response was normal or blunted. One patient's T3 levels decreased after TRH. All the patients (n=10) who had T3 levels within the hyperthyroid range showed a decrease after TRH. The decrease was significantly correlated (r=0.90) to the magnitude of the increase. No consistent T4 and no change in reverse-T3 response was obtained. The addition of T3, T4 or reverse-T3 determinations in connection with the TRH test does not seem to increase the discriminatory power of the test.

Unaltered 24 h serum PRL levels and PRL response to TRH in contrast to decreased 24 h serum TSH levels and TSH response to TRH in major depressive disorder

The 24 h serum levels of prolactin (PRL) and thyrotropin (TSH) assessed at ten different time points and the PRL and TSH responses to TRH administration (delta PRL, delta TSH) were investigated in 26 inpatients meeting the RDC criteria for an acute major depressive disorder. Fourteen of these patients were reinvestigated in a state of partial or complete remission. Comparison between the patients during both relapse and remission and 23 healthy controls showed no differences in the paramenters reflecting the 24 h PRL levels or delta PRL. However, significantly lower 24 h TSH levels and delta TSH were found in the patient group in the acute phase. Antidepressant medication, sedatives or the outcome of the dexamethasone test did not significantly influence the PRL levels or delta PRL. Both the patient group and the controls revealed normal sleep associated PRL release indicating unaltered serotoninergic and/or dopaminergic neurotransmission regulating the PRL secretion. The present results indicate a selective disturbance affecting the pituitary TSH secretion, and are consistent with our hypothesis that the mechanism behind the decreased TSH levels and the impaired TSH response to TRH in acute major depressive disorder involves a down-regulation of the pituitary TRH receptors.

Serum dopamine-beta-hydroxylase activity in patients with major depressive disorders

The dopamine-beta-hydroxylase (DBH) activity in serum was assayed in 32 acutely ill inpatients with major disorder and in 33 healthy control subjects. Twenty-six of these patients were also studied in a state of remission. The DBH activity was compared to the serum levels (studied during a 24 h period) of T4, T3, TSH, prolactin and melatonin as well as to the outcome of the dexamethasone suppression and TRH test and to various clinical symptoms, as estimated by different rating procedures. No significant differences in DBH activity were found between the acutely ill patients, patients in remission, or normal subjects. Thus, the determination of the activity does not seem to be of practical importance as a laboratory diagnostic tool for major depressive disorder. A significant positive correlation was found between the DBH activity and the TSH levels, estimated by several parameters during the 24 h period, in the acutely ill patients, whereas no significant correlation was found in patients in remission or in the normal subjects. No significant correlation was found between the DBH activity in any group and the other laboratory or clinical parameters. The mechanism behind the significant correlation between the DBH activity and TSH levels remains to be clarified.

Effect of TRH on TSH and prolactin levels in affective disorders

The thyrotropin-releasing hormone (TRH) test was studied in 32 patients with acute major depressive disorder, 16 patients with recurrent unipolar (n = 8) or bipolar (n = 8) affective disorder in remission, and 22 healthy control subjects. Twenty-six of the 32 acutely ill patients were also studied when in remission. Outcome in these patients was correlated to serum levels of triiodothyronine (T3), 3,3',5'triiodothyronine (reverse T3), thyroxine (T4), thyroid-stimulating hormone (TSH), prolactin (PRL), melatonin, dexamethasone suppression test (DST) results, and clinical symptoms assessed by the Comprehensive Psychopathological Rating Scale (CPRS). The TSH response to TRH (delta TSH) was decreased in the acutely ill patients, but no difference was found between patients in remission and controls. The delta TSH was correlated to TSH but not to T3 and T4 levels in both acutely ill and control subjects. In the acutely ill group, delta TSH did not distinguish between patients with normal and abnormal DST results. Thus, abnormalities in the hypothalamic-pituitary-thyroid (HPT) axis are not correlated to abnormalities in the hypothalamic-pituitary-adrenal (HPA) axis. Moreover, delta TSH did not differentiate between melancholic (DSM-III) and nonmelancholic patients or between patients with primary and secondary depression. No correlation was found between delta TSH and CPRS scores. Patients with observable agitation greater than 0.25 points (item range 0-3) had higher levels of delta TSH than patients with lower levels. No significant correlation was found between delta TSH and seven specific symptom clusters on the CPRS. However, there was a possible relation between low delta TSH and violent suicide attempts or suicide. PRL levels did not distinguish acutely ill patients from controls. Finally, there was no significant regression between delta TSH and melatonin levels. The decrease in delta TSH seen in the acutely ill patients was too small to be of diagnostic value as a laboratory measure differentiating acutely ill and healthy subjects. The mechanism underlying the HPT alterations in acute major depressive disorder may be a desensitization of the TRH receptor in the thyrotrophs secondary to an increased endogenous TRH stimulation.

Occult thyrotoxicosis in patients with chronic and paroxysmal isolated atrial fibrillation

Thyroid function tests, including thyrotropin releasing hormone administration (TRH), were performed in 40 consecutive patients with isolated atrial fibrillation (IAF) (i.e., without any other evidence of cardiac disease). The arrhythmia was chronic in 5 and paroxysmal in 35 patients. Thyrotoxicosis could not be diagnosed either clinically or by abnormal serum levels of T4, T3, T3 BC, and thyroid stimulating hormone (TSH). Thyroid stimulating hormone response to TRH, which was normal in 35 patients, was absent in 5 (12.5%) who were considered to have occult thyrotoxicosis. One had chronic and the other 4 had paroxysmal IAF. The arrhythmia did not recur after antithyroid treatment in these four patients who were in sinus rhythm after a mean follow-up period of 21 months. Full exploration of the thyroid function therefore seems useful not only in patients with chronic IAF, but also in those affected by the paroxysmal form.

Serum triiodothyronine and hyperthyroidism in a population sample of women

The serum T3 assay has been regarded as the most sensitive single test for hyperthyroidism although impaired conversion of T4 to T3 in non-thyroidal illness (NTI) might decrease its diagnostic sensitivity. The present report gives experience from the T3 assay in middle-aged females under conditions similar to those in a general health survey. The assays were performed during two periods with an interval of six years. In 1974-75 we studied a representative sample (n = 1283) of women of ages 44, 52, 56, 60 and 66 years in Göteborg, Sweden. Individuals with serum T3 concentration greater than mean + 2.5 SD were selected for a follow-up study (n = 21). Of 16 individuals with no previous thyroid disease and no present treatment with thyroid hormones or oestrogens, 14 were subjected to a TRH-stimulation test giving a normal TSH response in 10 cases having T3 concentrations up to mean + 3.5 SD. Four women with serum T3 concentration greater than or equal to mean + 3.5 SD had previously unrecognized autonomous function thyroid function, of whom two developed hyperthyroidism after two years. The original population sample was reinvestigated after six years in 1980-81 (n = 1138) together with an additional sample of women giving a total sample of 1422 women of ages 26, 38, 50, 58, 62, 66 and 72 years. Of the females studied in 1974-75 eight had developed hyperthyroidism between the two studies; three of these had raised serum T3 at the investigation in 1974-75. No case of hyperthyroidism had been missed by the T3 assay in the 1974-75 study. Of individuals with serum T3 greater than or equal to mean + 2.5 SD selected for a follow-up (n = 29) at least five were found to have previously unrecognized thyroid autonomy. We found a raised serum T3 to be associated with hyperthyroid (n = 2) and euthyroid Graves' disease, autonomously functioning thyroid adenoma(s), possible painless subacute thyroiditis, possible thyrotoxicosis factitia, diminished thyroid reserve and thyroid substitution therapy.

Serum reverse-T3 determinations in the laboratory diagnosis of hyperthyroidism

The relative discriminatory value of the estimation of the serum reverse-T3 levels for the laboratory diagnosis of hyperthyroidism was investigated in 47 patients with clinical signs or symptoms of hyperthyroidism. The results were compared with those from the determination of the total serum levels of T3 and T4 prior and after correction for the binding proteins. Twenty-three of the patients had normal thyroid function and 24 had hyperthyroidism. The estimation of the total serum T3 level was superior to both the determination of the total serum T4 and reverse-T3 levels even subsequent to correction for the binding proteins.

Serum T3 and T4 determinations during the TRH test as a complement to improved discriminatory power in suspect hyperthyroidism

The aim of the study was to determine whether the addition of T3 and T4 determination in connection with a routine TRH-test could increase the discriminatory power of the test. Thus, forty-one patients with suspect hyperthyroidism were examined and samples for T3 and T4 and TSH determinations were drawn prior to the administration of TRH and at 20 and 60 min thereafter. The results showed that the addition of these thyroid hormone estimations did not increase the clinical value of the TRH-test.

Radioimmunoassay of triiodothyronine and thyroxine in capillary blood

A radioimmunoassay technique for the estimation of T3 and T4 levels in capillary blood is described and evaluated in comparison to a simultaneously drawn and equally analyzed sample from the cubital vein. A total number of 236 samples thus received from the capillary and the vein from euthyroid, hypo- and hyper-thyroid patients were collected. For both T3 and T4 a good correlation (r = 0.94) was obtained. The clinical implication would especially be for paediatric practice.