T3 Uptake Test Research Articles

Development of hyperthyroidism in nodular goiter and thyroid malignancies in an area of relatively low iodine intake.

A high incidence of toxic nodular goiter has recently been described in areas of relatively low iodine intake. We studied the development of hyperthyroidism in nodular goiter and thyroid malignancies in an area of relatively low iodine intake (median 87 micrograms/h). The material comprised a total of 557 patients admitted to our department in the period 1978-88. The follow-up material consisted of 214 patients with a median age of 55 yr (19-86). Eighty-eight percent were females. The period of observation was 33 months (1-205). All patients had technetium thyroid scans, serum T3, serum T4, T3 uptake test and serum TSH performed. TRH tests were performed in 58 patients. During the follow-up period 45 initially euthyroid patients became hyperthyroid (18%). The incidence increased with age, and the median age in the group, who developed hyperthyroidism, was 65 yr. An estimated minimal incidence of toxic nodular goiter was 23/100,000/yr. Contrary to previous assumption, hyperthyroidism developed frequently in elderly patients with nodular goiter in a low iodine intake area. Thyroid cancer was found in 13 patients corresponding an estimated incidence of 1.5/100,000/yr. The cancer incidence was very low compared to other nordic countries with high iodine intake. This finding may suggest a possible influence of iodine intake on the incidence of thyroid cancer.

Thyroid function tests in patients with acquired immune deficiency syndrome and healthy HIV1‐positive out‐patients

The thyroid function tests as well as evidence of thyroiditis were studied in 18 male patients with acquired immune deficiency syndrome (AIDS) and 12 healthy HIV1-positive persons compared with an age-matched control group. Serum total thyroxine was not significantly different between the groups, but both serum total triiodothyronine, triiodothyronine uptake test, and free thyroid hormone indices showed significantly decreasing values from HIV1-positive healthy persons to AIDS patients compared with controls (P value from less than 0.05 to less 0.001). Serum TBG was elevated in HIV1-positive subjects and in patients with AIDS, with a significant inverse correlation with the T3-uptake test (Spearman's rho = 0.657, P less than 0.01). There was no correlation between thyroxine binding globulin and the other measured variables. The serum level of thyrotropine was not significantly different in the groups, whereas serum thyroglobulin was significantly lowered in the AIDS group. There was no correlation between thyroid function variables and survival time, hepatic function and ratio of T-helper to T-suppressor cells. No evidence of thyroiditis was observed. In conclusion thyroid tests showed an atypical outcome in HIV1-positive patients with or without AIDS compared with the pattern normally seen in non-thyroid illness, and should, therefore, caution the interpretation of the biochemical changes when diagnosing abnormal thyroid function in these patients.

Abnormalities in thyroid function associated with chronic therapy with methadone.

We studied 145 clinically euthyroid patients on maintenance methadone therapy for narcotic withdrawal, to characterize abnormalities in thyroid-function tests induced by methadone. About a third had increased total thyroxin (T4) and total triiodothyronine (T3) concentrations in serum. The mean concentrations of T3, T4, and thyroxin-binding globulin (TBG) in serum were significantly greater (P less than 0.001 each) in these patients than in a euthyroid control group. There was a corresponding decrease in the T3 uptake (T3U) test, but the free thyroxin index (FTI) failed to correct for the increased TBG concentration in 15.9% of the patients. Individual and mean concentrations of free T3 (FT3) and free T4 (FT4) in serum and results of an "ultrasensitive" test for thyrotropin (TSH-IRMA) were within normal limits and confirmed the euthyroid state. We conclude that prolonged therapy with methadone causes increases in TBG, T3, and T4 in serum. FT3, FT4, and TSH-IRMA estimations are recommended as the diagnostic thyroid tests to use for patients on methadone maintenance therapy.

Thyroid hormone concentrations and free thyroxine status in neonatal venous and capillary serum pairs.

The levels of thyroid hormones in paired venous and capillary serum samples taken from 68 healthy full-term neonates were determined by radioimmunoassay. Compared with capillary values, total thyroxine (T4), thyrotropin (TSH) and thyroxine-binding globulin (TBG) each showed a significant decrease in venous serum. The mean venous and capillary concentrations of tri-iodothyronine (T3), reverse tri-iodothyronine (rT3) and free thyroxine (fT4) were not significantly different; however, in each case the fitted linear relationship suggested that venous and capillary values were not concordant (P less than 0.02, P less than 0.01, P less than 0.05 respectively). Both the T3 uptake test and the free thyroxine index (FTI) were significantly higher in venous serum, while the ratios of T4 to TBG in paired samples were equivalent. These results suggest that consistent sample collection and assay methods should be applied when assessing neonatal thyroid status, particularly if comparison of results is intended.

Cluster-oriented discriminant analysis; taxonomic classification of the thyroid function

A computer assisted procedure for the diagnosis of thyroid diseases, based on seven clinical chemical parameters, is proposed. The population studied consisted of 592 consecutive outpatients with a tentative diagnosis of thyroid disease. Thyroxine, triiodothyronine, T3 uptake test, TSH before and after TRH application, its difference and thyroxine binding globulin have been determined. The patients were clinically examined and in each case a Tc-scintigram was obtained. As a first step, 20 biochemical patterns were defined by cluster analysis (pattern cognition). To check how good the grouping process was, linear discriminant analysis was applied after which the reclassification rates were very satisfactory. The clusters found corresponded well to the pathophysiological situations with some exceptions. As a second step, patients were assigned to these patterns by use of the derived discriminant functions (pattern recognition). The proposed method seems to have some advantages over other diagnostic models published hitherto.

Long-term variability in serum thyroglobulin and thyroid related hormones in healthy subjects.

From 5 young males and 5 young females blood was drawn under highly standardized conditions at 6 to 10 occasions during 4 months. The serum constituents thyroglobulin, thyroxine, triiodothyronine, T3-uptake test, TBG and TSH were determined, and four indices were calculated. The biological intra-individual coefficients of variation were below 0.14 for thyroglobulin, and the inter-individual coefficients for variation ranged from zero for T3-uptake test to 0.35 for thyroglobulin. All results were within the generally accepted reference ranges for normals. Within these ranges the calculations of indices for free thyroxine and triidothyronine according to T3-uptake test and TBG, did not significantly reduce the coefficients of variation for these serum constituents. Thyroglobulin concentrations did not correlate to any of the measured or calculated constituents. The knowledge of these intra- and inter-individual variations of serum thyroglobulin in healthy persons is of importance for the interpretation of variations found in patients.

Effect of anticonvulsant and antidepressant drugs on iodothyronines in serum.

Serum iodothyronine concentrations were measured in patients on long-term therapy with one or two anticonvulsant drugs. Diphenylhydantoin (DPH) and carbamazepine (CBZ) reduced the serum levels of thyroxine (T4) free T4 index, reverse triiodothyronine (rT3) and 3,3'-diiodothyronine (3,3'-T2), whereas the depressant effect on the serum levels of triiodothyronine (T3) and free T3 index was small but statistically significant. In patients administered DPH and phenobarbital (PB) or CBZ and primidone (PD) the serum iodothyronine levels were also depressed, except for normal T3 and free T3 index. Patients receiving only PB or PD had normal serum levels of total and free thyroid hormones, but decreased concentrations of rT3 and 3,3'-T2. Only supratherapeutic concentrations of DPH and CBZ added in vitro to control sera significantly reduced the number of T4 and T3-binding sites, as reflected in increased T4 and T3 uptake test results. This indicates that the DPH and CBZ-induced decrease in thyroid hormone concentrations in vivo is not due to a displacement of thyroid hormones from their binding sites on serum proteins. The antidepressant drugs amitriptyline and mianserin had no effect on the thyroid hormone levels in serum.

The influence of chronic renal failure on serum and urinary thyroid hormone levels.

ABSTRACT The effects of various degrees of chronic renal failure on serum and urinary thyroid hormones were studied in 10 patients with a mean creatinine clearance (Cr.Cl.) of 23 ml/min (group A), in 11 patients with a Cr.Cl. of 5.7 ml/min (group B), and in 60 healthy euthyroid subjects with normal renal function. We found a significant decrease (P < 0.01) of serum total thyroxine (T4) (5.3 ±1.9 (sd) μg/100 ml in group A and 4.1 ± 1.5 in group B), serum total triiodothyronine (T3) (65.4 ± 17.4 ng/100 ml ~57.4 ± 13.9), serum free T4 (5.60 ± 1.74 arb.U ∼ 4.45 ± 1.61), and serum free T3 (69.51 ± 21.22 arb.U ∼ 62.09 ± 12.39). T3 uptake test and basal thyroid stimulating hormone (TSH) values were normal in both groups of renal patients. No statistical significance was found in T4 excretion in urine. Urinary T3 excretion was significantly reduced (P < 0.01) in group A (27 ± 44 ng/24 h), and undetectable in terminal renal failure. Urinary protein excretion was non-selective and low (median 0.2 g/24 h and 0.7 g/24 h, respectively). Conclusively we have found reduced levels of serum total and free T3, and in contradiction to most investigators substantially reduced levels of serum total and free T4. Urinary excretion of T4 and T3 reflects the low levels of free serum hormones and the tubular impairment.

Acute effects of alcohol on anterior pituitary secretion of the tropic hormones.

The plasma or serum concentrations of GH, TSH, LH, PRL, testosterone, cortisol, T4, and T3, and the values of the T3 uptake test were monitored in 12 healthy male volunteers for a period of 20 h after administration of one large dose of ethanol (1.5 g/kg BW). The effects of TRH and LRH on the secretion of TSH, PRL, and LH were studied in these subjects once during the period of acute alcohol intoxication (4 h after the start of drinking) and once during the hangover period (14 h after the start of drinking). Each subject served as his own control by drinking water only during another experimental session. Alcohol had no significant effect on basal concentrations of GH, TSH, LH, T4, T3, or testosterone. The concentration of cortisol in plasma was elevated during the whole 20-h period after ingestion of alcohol, as compared with the control values. Alcohol also did not significantly alter the effects of TRH and LRH on plasma TSH and LH levels at 4 and 14 h. During the hangover period, the PRL response to TRH was totally blocked, but during alcohol intoxication, there was a slight increase in the PRL response to TRH. The lack of response of PRL to TRH during the hangover suggests that withdrawal symptoms are associated with increased dopaminergic activity in the hypothalamus.

THYROID FUNCTION TESTS IN PATIENTS ON LONG‐TERM TREATMENT WITH VARIOUS ANTICONVULSANT DRUGS

Thyroid function tests were studied in patients undergoing long-term treatment with various anticonvulsant drugs. Previous reports that diphenylhydantoin induces a decrease in the serum concentrations of total and free thyroxine (T4) and triiodothyronine (T3) without a change in the TSH concentration were confirmed. Diphenylhydantoin had no effect on reverse T3. Carbamazepine was also found to decrease serum T4, the free T4 index and T3 but, with the exception of T3, the decrease was smaller than that induced by diphenylhydantoin. Dipropylacetic acid did not influence the serum thyroid hormone concentrations, and neither did primidone. This demonstrates that the interaction between anticonvulsant drugs of different chemical structure and thyroid hormone metabolism is diverse. None of the drugs tested altered serum TSH or the T3 uptake test for the estimation of unsaturated thyroid hormone binding-capacity in serum. These two tests are considered diagnostically more dependable than the measurement of thyroid hormones in serum when diphenylhydantoin and carbamazepine are administered.

Clinical value of total T4 and T3 determinations in patients with suspect hyperthyroidism before and after correction for binding proteins.

ABSTRACT. In a previous Investigation we found that the determination of serum T3 by a radioimmunoassay procedure was superior to both the determination of serum T4 and the TRH test for laboratory discrimination between eu‐ and hyperthyroidism. The investigation comprised 50 patients in whom hyperthyroidism could not be excluded by the first clinical examination alone. The complete investigation showed that 26 of the patients had hyperthyroidism and 24 had normal thyroid function. The aim of the present study was to elucidate whether the discriminatory power of T3 and T4 estimations in these patients could be increased by correction for variations in the hormone‐binding proteins. The influence of the proteins was estimated by the T3 uptake test and determination of the TBG level by radioimmunoassay technique. The free T4 and T3 indices were calculated according to standard procedure. The results demonstrate that all subjects had TBG values within the reference levels. In the discrimination between normal and hyperthyroid states, the kee T4 index gave more reliable results than the uncorrected T4 or the T4: TBG ratio. However, the discriminatory power of T3 was superior to both T4, T4: TBG ratio and free T4 index. No improvement was obtained by calculation of the T3: TBG ratio. A slight improvement was obtained by calculation of the free T3 index. It is concluded that estimation of the total serum T3 level is superior to the total serum T4 level in the laboratory discrimination between euand hyperthyroidism even subsequent to correction for the binding proteins.

Sulphonylurea and hypothyroidism in Nigerian diabetic subjects.

Thyroid function has been assessed using the T3-Uptake test in 98 nigerian diabetic and 50 non-diabetic control subjects. Whilst abnormal tests suggestive of thyroidal hypofunctional state were commoner in the group on chlorpropamide alone, and in combination with metformin, these were unrelated to the duration of treatment. In addition, none had clinical hypothyroidism.

Adaptation of a T3-Uptake Test and of Radioimmunoassays for Serum Digoxin, Thyroxine, and Triiodothyronine to an Automated Radioimmunoassay System—"Centria"

We report the adaptation of four radioassays to the prototype of an automated radioimmunoassay system ("Centria," Union Carbide). The system consists of three integrated modules: (a) an automated pipettor, which dispenses samples and reagents; (b) the key module, an incubator/separator, in which centrifugal force is used to initiate and terminate multiple radioassay incubations and separations simultaneously; and (c) a gamma-counter/computer, which counts three tubes simultaneously and converts counts into concentration units. Radioimmunoassays for thyroxine, triiodothyronine, and digoxin were developed with use of well-characterized antibodies and of prepackaged Sephadex-containing columns to separate bound and free radioactive ligand. A triiodothyronine-uptake test in which the same kind of columns were used was also adapted to the instrument. Results for clinical samples compared favorably with those obtained by manual procedures. We report data on correlation between different methods and preliminary data on precision of the prototype system.

AUTOMATIZATION OF SERUM THYROXINE DETERMINATION AND OF T3-UPTAKE TEST

Simple, rapid and inexpensive techniques were developed, since in this laboratory the requests for determinations of T4 an of T3-uptake exceed the number of 200 per week. This study was aimed at the development and the automatization of a competitive protein binding method for T4 on the basis of the automatic T3-uptake test in use.

Dolphin thyroid: Some anatomical and physiological findings

1. Plasma thyroxine (T4), protein bound iodine (PBI), inorganic iodine, total iodine, thyroxine binding globulin (TGB), unsaturated TBG (resin T3 uptake test) and free thyroxine were measured in a series of tests on two species of porpoise (or dolphins) and two species of small whales. This was the first such work done on cetaceans. The values presented for the bottlenose dolphin, Tursiops truncatus, were derived from 86 plasma specimens from 31 different animals (Table 2) and should be clinically useful for the future diagnosis of thyroid disease in that species. 2. A total of twenty-four plasma specimens from the Pacific white-striped dolphin, Lagenorhynchus obliquidens (Fig. 3), the killer whale Orcinus area (Fig. 4) and the pilot whale Globicephala scammoni (Fig. 5) gave values that must be regarded as preliminary until a larger number of animals can be sampled. 3. All of these marine cetaceans have larger thyroids and smaller body surface areas than terresterial mammals of comparable weight. 4. In bottlenose dolphins and Pacific white-striped dolphins the total thyroid weight is about 2.25 times the total adrenal gland weight. The adrenals and the thyroid are both about one-third larger (on a gland weight to body weight basis) in Pacific white-striped dolphins. 5. Differences in water temperature of 6° C to 9° C did not appear to affect the plasma thyroid indices of bottlenose dolphins or killer whales (Fig. 4). A 72-hour fast caused an increase in plasma T4 levels of each of 3 bottlenose dolphins with an average rise of 1.2 μg/100 ml. 6. The high level of plasma T4 and PBI appear to correlate well with the relatively high metabolic rate observed in T. truncatus. However, the species that appears to have the highest metabolic rate, the Pacifie white-striped dolphin, Lagenorhynchus obliquidens (Fig. 3), had the lowest plasma level of T4, PBI, total iodine, TGB capacity and cholesterol (Table 2). This data points out the need for a comprehensive study of thyroid function in wild and captive white-striped dolphins and other species that are difficult to maintain in captivity.

Factors influencing in vitro tests of thyroid function in the elderly.

AbstractDeterminations of erythrocyte or resin I131‐triiodothyronine (T3) uptake and the serum protein‐bound iodine (PBI) concentration were made in 39 elderly patients on a geriatric ward and (for controls) on 20 relatively healthy residents of an old people's home.Difficulties in interpretation of these two tests of thyroid function may arise from a quantitative or qualitative alteration in thyroxine binding to protein. Some circumstances in which these test findings were altered in old people in the absence of clinical evidence of thyroid abnormality included accidental hypothermia, infections and the ingestion of certain drugs commonly used in geriatric practice, e.g., anabolic steroids. Results of the resin T3 uptake test were also more variable in elderly hospital patients than in normal old or young people. The changes in thyroxine binding by protein during administration of anabolic steroids were not due to competitive binding but to a reversible reduction in the amount of thyroxine‐binding protein.When determinations of thyroid function by in vitro tests are questionable, the free‐thyroxine index (the product of the T3 uptake and the PBI level) gives a true assessment of thyroid status.

SERUM TRI-IODOTHYRONINE UPTAKE USING COATED CHARCOAL IN THE ASSESSMENT OF THYROID FUNCTION

SUMMARY A modification of the tri-iodothyronine T3 uptake test using coated charcoal has been developed. When the method was compared with the resin sponge test, the charcoal method was found to be more rapid, accurate and economical. For patients who were not pregnant or receiving drugs known to affect the degree of saturation of thyroxine-binding globulin, the T3 charcoal uptake method made a good distinction between the hyperthyroid and euthyroid patients but the distinction between the hypothyroid and euthyroid patients was less satisfactory. Separation between the three groups of patients was improved by using the product of the T3 uptake and protein-bound iodine measurement (the free thyroxine index). The [125I]T3 charcoal results are reported for 199 blood donors as normal controls. A sex difference was apparent but there was no significant variation in the age groups studied (18–60 yr.). Thirty-seven pregnant women were studied. Calculation of the free thyroxine index did not give results within the non-pregnant euthyroid range.

Triiodothyronine in pregnancy

The radioactive T3 uptake test is a relatively simple laboratory procedure which indirectly measures circulating T3, the active fraction of the thyroid hormone. The present study applies this test to the three trimesters of pregnancy, the postpartum period, and to inevitable and incomplete abortions. The mean of these values shows a slight drop in T3 in the first trimester, a rather marked drop in the second and third trimesters, and a return to euthyroid levels by the sixth postpartum week. There are no significant changes with inevitable or incomplete abortions. Individual readings, however, are so variable and unpredictable that they cannot be used reliably to confirm clinical suspicion of a thyroid disorder. The variations in the mean values of circulating T3 are correlated with the physiologic changes of pregnancy.

The application of a corrected hematocrit to triiodo-L-thyronine I-131 red blood cell uptake test.

1) The validity of using the corrected hematocrit, which was obtained on the basis of assuming that 85μ3 is the ideal corpuscular volume for red blood cells, was discussed. 2) Ninety-two patients were examined by the T3 uptake test, and comparison of the data, obtained by Hamolsky's and Adams' calculations as well as by modified ones applying the corrected hematocrit, was done. 3) The work presented here showed fundamental difference in the locations of the boundaries between the three different diagnostic categories of thyroid function introduced by Adams et al. and Hamolsky et al. 4) This report showed higher labeling of T3 by red blood cells than Hamolsky's reports. The range of K for the euthyroid group was narrower mthis work than in the Adams' report. 5) The results obtained by using the corrected hematocrit on Hamolsky's and Adams' calculations showed better separation between the three diagnostic categories. As long as the corrected hematocrit was applied on Hamolsky's and Adams' calculations, both methods were equally valid to separate the three diagnostic categories.