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PubMed1977

A reassessment of 8-anilino-1-naphthalene sulphonic acid as a thyroxine binding inhibitor in the radioimmunoassay of thyroxine.

The effectiveness of 8-anilino-1-naphthalene sulphonic acid (ANS) in the radioimmunoassay (RIA) of thyroxine (T4) as an inhibitor of the binding of T4 to serum T4-binding proteins is assessed. The optimum ANS concentration is dependent upon the antiserum and the method used for separating free and bound T4. If T4 binding to serum proteins is not completely inhibited, resin separation methods may yield low values, while polyethylene glycol and double-antibody methods may produce high values for T4 concentration. Even with optimum ANS concentration gross errors in measurement of T4 may occur in patients with high thyroxine-binding globulin (TBG) concentrations.

Anilino Naphthalenesulfonates↗
PubMed1984

Thyroxine and thyroxine-binding globulin: discriminant formulae for the separation of the diagnostic classes of thyroid function.

The biochemical classification of thyroid functional status is often accomplished by the use of the thyroxine to thyroxine-binding globulin (T4:TBG) ratio. It has recently been shown, however, that the reference range of the T4:TBG ratio varies with the concentration of TBG. This makes the T4:TBG ratio an unwieldy diagnostic index. A more accurate and economical way to define thyroid function using T4 and TBG measurements is by linear discriminant formulae. This is so because T4 varies linearly with TBG at the T4 reference limits over a wide range of TBG concentrations. Using the T4 reference ranges established by Attwood and Atkin (Ann Clin Biochem 1982; 19: 101-3), the following formulae are obtained: T4 (nmol/l)--4.05 TBG (mg/l) greater than 94.5 indicates hyperthyroidism; T4 (nmol/l)--2.72 TBG (mg/l) less than 23.8 identifies hypothyroidism.

Humans↗
PubMed1990

Non-isotopic, two-step free thyroxine immunoassay: a better measure of free thyroxine than analogue radioimmunoassay.

Plasma or serum free thyroxine (T4) was measured by a novel non-isotopic, two-step immunoassay in 373 consecutive patients attending a thyroid clinic, in whom thyroid status was categorized according to clinical findings, supported by routine thyroid function tests. The 95% confidence limit of free T4 in the euthyroid patients (n = 112) was 7-20 pmol/L. Free T4 concentrations within the reference range were found in six of 40 patients with primary hypothyroidism and nine of 182 patients with overt thyrotoxicosis, six of whom had T3 toxicosis. Serum or plasma free T4 measured by the two-step method showed improved diagnostic specificity over an analogue RIA in selected groups of euthyroid patients in whom abnormal binding of analogue T4 can affect the validity of the result. Free T4 results found by analogue RIA and the two-step method in 58 patients who were receiving thyroxine replacement therapy were similar. The between-assay precision of the two-step method was poor ranging from a coefficient of variation of 9.7% to 19.3% over a free T4 concentration range of 5.0 to 46.0 pmol/L. We conclude that the two-step methodology offers diagnostic advantages for a laboratory which receives specimens from such patients for exclusion of thyroid disease but that improved assay precision is required before it could be used in a routine situation.

Autoantibodies↗
PubMed1992

New automated nonisotopic immunoassays for free thyroxin: effect of albumin and thyroxin-binding globulin concentrations.

Recently, nonisotopic (often automated) immunoassays for measuring serum free thyroxin (FT4) have become available. Though more costly than radioimmunoassays, they are considerably more convenient. We studied the influence of endogenous albumin and thyroxin-binding globulin concentration on five automated, nonisotopic methods of measuring FT4 [Enzymun on ES300 (one-step), Stratus I and II (essentially two-step), Delfia (two-step), and IMx (two-step)] in a mixed patient population. We observed that they (a) are influenced very little by endogenous serum binding proteins and (b) seem to have sufficient within-run precision to justify performing single measurements on patients' specimens.

Autoanalysis↗
PubMed1976

A new extractant for serum thyroxine by enzymatic digestion of thyroxine binding proteins.

The use of a pepsin solution to digest serum proteins results in quantitative release of thyroxine from carrier proteins. This extraction method greatly simplifies the original Murphy and Pattee (1) competitive protein-binding assay for serum thyroxine. The simplicity and efficiency of this extractant suggest that it may have application in radioimmunoassay and competitive protein-binding assay for nonpeptide ligands in serum.

Evaluation Studies as Topic↗
PubMed1983

[Evaluation on the interaction between thyroxine binding globulin (TBG) and thyroxine (T4) in healthy subjects and pregnant women].

A very simple method for the evaluation of the interaction between thyroxine binding globulin (TBG) and thyroxine (T4) has been developed and evaluated in 6 healthy subjects and 5 pregnant women. Rabbit anti-human TBG antiserum was precipitated with 50% ammonium sulfate followed by passing a DEAE-cellulose column. Immunoglobulin G (IgG) fraction thus prepared was covalently attached on a Sepharose CL-4B and used as an immunoadsorbent of serum TBG. After treatment with charcoal to remove endogeneous thyroid hormones, 10 microliter of sera from 6 healthy subjects and 5 pregnant women were incubated with 125I-T4 and various concentrations of cold T4 followed by immunoadsorption with anti-TBG-Sepharose, and association constants (Ka) between TBG and T4 were calculated in each subject using Scatchard's plot. The Ka value thus obtained in 6 healthy subjects was 1.47 X 10(8) M-1 (SD = 0.24), and in 5 pregnant women it was 0.82 X 10(8) M-1 (SD = 0.21) which was significantly lower than that of healthy subjects (P less than 0.001). Our present method does not need purification of TBG from serum to investigate its functions, especially in relation to the binding with thyroid hormones. Also, only a very small amount (100 approximately 150 microliter) of serum is enough for the calculation of Ka between T4 and TBG. The whole procedure is very easy to perform and can be done in a relatively short time, and therefore we consider this method clinically relevant and useful.

Adult↗
PubMed2001

Reference intervals from birth to adulthood for serum thyroxine (T4), triiodothyronine (T3), free T3, free T4, thyroxine binding globulin (TBG) and thyrotropin (TSH).

Disorders in thyroid function can impair normal development in children. Therefore it was our aim to establish reference intervals for serum triiodothyronine (T3), free T3 (fT3), thyroxine (T4), free T4 (fT4), thyroxine binding globulin (TBG) and thyrotropin (TSH) which are applicable from birth to adulthood by using the non-isotopic automated chemiluminescence immunoassay system, Immulite (DPC Los Angeles, USA). Serum samples from 762 euthyroid newborns, children and adolescents (369 female, 393 male; age 1 day to 19 years) were examined; of these, 381 were classified as pubertal. Due to non-normal distribution, the 2.5th, 50th and 97.5th percentiles (the central 95% interval) were calculated for each group. The median concentrations of T4, fT4 and TSH were up to 3.2-fold higher during the first 2 weeks, while T4 increased during the first month of life. The concentrations in all age groups showed no sex differences. From 1 year onwards, the concentration of all parameters tended to decrease until adult age, with the exception of TBG which increased by >60% (p<0.02) and reached a maximum at approximately 5 years of age. The findings underscore the fact that thyroid hormones are not associated with sexual development, except for TBG, which decreased slightly (p<0.04) between Tanner stages 1 and 5. However, the reference intervals established here demonstrate that marked changes occur in concentrations of thyroid hormones after the neonatal period. Our findings complement these of earlier studies. The developed reference intervals can be used to assess the thyroid status of patients, particularly if the measurements are done on the Immulite/Immulite 2000 system.

Adolescent↗
PubMed1991

Patterns of plasma sex hormone-binding globulin, thyroxine and thyroxine-binding globulin in relation to reproductive state and hibernation in female little brown bats.

A sex hormone-binding globulin (SHBG), which bound both oestradiol and dihydrotestosterone, was studied in the plasma of adult female little brown bats throughout the annual reproductive cycle. This protein was present at low baseline levels from September to May inclusive, months which correspond to the periods of hibernation, ovulation and early pregnancy. During the second half of pregnancy in June, SHBG levels increased 15- to 30-fold and remained increased throughout lactation and anoestrus/prooestrus (July-August). Although SHBG was increased during late pregnancy, the fact that levels were also high during and after lactation indicates that this protein is not specific to pregnancy. Plasma concentrations of thyroxine (T4) and the percentage binding of T4 to thyroxine-binding globulin (TBG) also showed marked seasonal variations, with T4 levels exhibiting a biphasic seasonal pattern. A major peak in plasma concentrations of T4 occurred around the time of spring arousal from hibernation and subsequent ovulation, while a second peak of lesser magnitude was measured in August, corresponding to the time of pro-oestrus and the onset of mating. The percentage binding of T4 by TBG was increased during the summer months in parallel with the increase in SHBG concentrations. Electrophoretic analysis of plasma T4 binding revealed a single peak of TBG activity throughout most of the year; however, during the early lactational period TBG was resolved as a double peak, suggesting the presence of a molecular variant during this reproductive stage.

Animals↗
PubMed1992

Dependence of free thyroxine estimates obtained with equilibrium tracer dialysis on the concentration of thyroxine-binding globulin.

Some equilibrium dialysis determinations of free thyroxine (T4) vary directly with thyroxine-binding globulin (TBG) concentration. This apparent TBG dependence has been limited to methods involving radiolabeled T4 added to the dialysis system (tracer dialysis). In this study we compared tracer dialysis with direct dialysis for determining free T4 and obtained the following results (mean +/- SD) for patients with hypothyroxinemia of nonthyroidal illness (23.8 +/- 10.7 vs 24.2 +/- 10.9 pmol/L, P greater than 0.8), patients with congenital TBG deficiency (11.4 +/- 2.2 vs 16.2 +/- 7.1 pmol/L, P greater than 0.05), normal control subjects (32.7 +/- 6.5 vs 18.5 +/- 5.8 pmol/L, P less than 0.001), and pregnant women (31.2 +/- 8.7 vs 12.1 +/- 2.6 pmol/L, P less than 0.001). Direct dialysis determinations were independent of TBG and total T4. Tracer determinations were greater than direct determinations in normals, a discrepancy that increased in pregnancy. Tracer determinations correlated significantly with total T4 and TBG concentrations (P less than 0.001). TBG and total T4 dependence in the tracer method was attributable to small overestimations of the free fraction of T4. Similar overestimations multiplied by increasing total T4 concentrations resulted in greater errors. Relative to results for normal sera, the tracer method overestimated free T4 when total T4 was increased and underestimated free T4 when total T4 was decreased.

Adolescent↗
PubMed1991

[Normal values for free thyroxine, free triiodothyronine, reverse triiodothyronine, thyrotropin, thyroglobulin and thyroxine-binding globulin in umbilical cord blood of healthy mature newborn infants].

The venous cord blood levels of free thyroxine (fT4), free triiodothyronine (fT3), reverse triiodothyronine (rT3), thyrotropin (TSH), thyroglobulin (TG) and thyroxine binding globulin (TBG) were studied in 56 mature and healthy newborns. Newborns with a gestational age less than 37 or more than 42 weeks, a delivery by forceps or cesarian section, a birth-weight less than 2500 g, a pH-value of the cord-artery blood less than 7.15, an Apgar-value after 1 minute less than 7 were excluded from the study. All mothers were non-smokers. The values of fT4 were 18.66 +/- 4.18 pmol/L, of fT3 were 1.59 +/- 0.75 pmol/L, of fT3 were 2152 +/- 666 pg/ml, of TSH were 7.83 +/- 4.49 mU/ml, of TG were 44.61 +/- 23.84 ng/ml, and of TBG were 25.61 +/- 5.42 micrograms/ml. A weak negative correlation was found between the TG-value and the pH-value of the cord-artery blood (r = -0.27, y = 191.55 - 22.82.x, p less than 0.05), and between the fT4 values and the gestational age (r = -0.34, y = 67.53-1.22.x, p = 0.01). The rT3-values were positively correlated to the gestational age (r = 0.29, y = -4571 + 167.x, p less than 0.03).

Female↗
PubMed1979

Effect of ACTH-stimulated glucocorticoid hypersecretion on the serum concentrations of thyroxine-binding globulin, thyroxine, triiodothyronine, reverse triiodothyronine and on the TSH-response to TRH.

The responses of serum concentrations of TSH, thyroxine (T4), triiodothyronine (T3) and of reverse triiodothyronine (rT3) to i. v. administration of 0.4 mg THR were examined prior to (and after) i. m. administration of ACTH (2 mg Synacthen Depot) in 7 euthyroid women using estrogen-containing oral contraceptives and in 8 controls, with the following results: (1) an increase in endogenous glucocorticoid secretion is associated with a depression of the TSH response to TRH; (2) TSH formed in decreased amounts is still capable of stimulating thyroid secretion; (3) the increased serum corticoid levels fail to affect the secretory response of the thyroid to TSH; (4) control of the pituitary-thyroid axis remains normal in the presence of increased serum thyroxine-binding globulin (TBG) levels. In a further series the serum levels of TBG, T4, T3, rT3 and cortisol under the effect of ACTH-induced endogenous glucocorticoid hypersecretion were studied in 6 normal untreated controls, in 6 normal women using oral contraceptives and in 10 untreated hyperthyroid patients. During four days subsequent to treatment the serum TBG levels decreased, maximum decrease being found in the users of oral contraceptives, minimum decrease in the controls. Serum T4 was found to decrease during 2 to 4 days, serum T3 parallel with an increase in serum rT3, for 1 to 2 days, subsequent for ACTH loading. In the euthyroid cases also the serum TSH levels showed a transitory decline. It is concluded that in case of endogenous hyperproduction of glucocorticoids (1) T4 leads to T3 monodeiodination decreases and T4 leads to rT3 conversion increases parallel with the changes in the serum cortisol levels; (2) TBG synthesis is inhibited by endogenous glucocorticoids; (3) the changes in serum TBG levels are accompanied by a decrease in the serum T4 concentrations.

Adrenocorticotropic Hormone↗
PubMed1986

Concentration of free thyroxin in serum of a patient with euthyroid hyperthyroxinemia secondary to increased thyroxin-binding prealbumin: results by various methods compared.

We used various kits to measure free thyroxin (T4) in serum from a patient with the very rare syndrome of euthyroid hyperthyroxinemia secondary to increased thyroxin-binding prealbumin in serum. This patient's free T4 by equilibrium dialysis was 13 ng/L (normal 9-21), whereas the free-T4 index was 18.6 (normal 5.5-11.5). Using six different commercial methods, the last three listed being T4-analog methods, we measured the serum free T4 in this patient. The mean +/- SD (and normal range) free-T4 concentrations (ng/L) measured were: GammaCoat, Two-Step, 19.2 +/- 4.5 (6.9-26.9); Liquisol, 17.8 +/- 3.0 (12.4-20.8); Immo Phase, Two-Step 26.8 +/- 0.3 (12.4-21.2); GammaCoat, Single-Step, 19.7 +/- 5.7 (10.3-21.0); Immo Phase, Single-Step, 27.7 +/- 0.9 (8.6-25.0); and Amerlex, 14.1 +/- 0.6 (5.3-14.1). In four patients with familial dysalbuminemic hyperthyroidism, in whom the serum T4 by equilibrium dialysis was normal, all three T4-analog methods gave results far exceeding normal (greater than 50 ng/L).

Humans↗
PubMed1977

Free thyroxine index or effective thyroxine ratio?

The ability of the free thyroxine index (FTI) and the effective thyroxine ratio (ETR) to distinguish abnormal from normal thyroid function is compared in a series of 422 patients; they were equally successful in detecting hyperthyroidism. In hypothyroidism, however, the ETR values of 22% were within 95% 'normal' limits compared with 7,4% of the FTI values. Other authors have shown a similar poorer sensitivity of the ETR compared with the FTI.

Humans↗
PubMed1982

Effect of thyroxine on molecular properties of native and dansylated thyroxine-binding globulin.

The effect of thyroxine (T4) on the stability of thyroxine-binding globulin (TBG) was investigated by examining intrinsic (tryptophan) or extrinsic (DNS) fluorescence as structural probes to demonstrate the presence of an induced conformation change. A thermal transition was observed at 55 degrees C for TBG by Trp fluorescence, which is evidence for heat denaturation, whereas no transition was observed in the same temperature range for TBG-T4. Acidification of DNS-TBG at pH 4.4 produced a decrease in both Trp and DNS fluorescence whereas DNS-TBG-T4 at the same pH showed a large change in DNS fluorescence but no change in Trp fluorescence. Low guanidinium chloride concentration unfolded the unliganded molecule as indicated by a decrease of Trp and DNS fluorescence, whereas the fully occupied TBG showed only a decrease of DNS fluorescence. Exposure of TBG and TBG-T4 to trypsin showed a twofold increase in the rate of tryptic hydrolysis for TBG-T4 indicating that T4 binding either increased the exposure to the solvent of some lysyl or arginyl residues or increased their susceptibility to the trypsin action. These data provide additional evidence that T4 binding enhances the molecular stability of TBG. An effect on TBG conformation which was previously described probably explains the increased stability. The decrease in dansyl fluorescence of DNS-TBG-T4 probably is due to a local effect of acid or GdmCl unrelated to protein unfolding.

Alpha-Globulins↗
PubMed1983

Free triiodothyronine and free thyroxin in sera of pregnant women and subjects with congenitally increased or decreased thyroxin-binding globulin.

Concentrations of free thyroxin (T4) and free triiodothyronine (T3) were measured in sera from pregnant women, in subjects with congenitally increased or decreased thyroxin-binding globulin (TBG), and in euthyroid controls. Measured free hormone concentrations were compared with calculated values for free hormone derived from concentrations of total T4, total T3, and binding proteins. Measured and calculated concentrations of free T4 and free T3 were below normal in the pregnant subjects but were normal in subjects with congenital increases of TBG. The low concentrations of free hormone in pregnancy are at variance with the euthyroid status of these subjects. Measured free T4 was normal, but concentrations of free T3 were less in the euthyroid congenitally low-TBG group.

Adolescent↗
PubMed1984

[Serum thyroxine (T4) levels and thyroxine-binding capacity of patients with corticosteroid-dependent and atopic bronchial asthma].

The patients with bronchial asthma, treated a long time with corticosteroid s (the so called cortico-dependent bronchial asthma) are an adequate model for the study on the dependence between the function of the thyroid gland and the effect of glucocorticosteroids. The study was carried out on 12 patients with atopic, 14--with cortico-dependent bronchial asthma and II--healthy subjects. The function of the thyroid gland was assessed by the serum level od thyroxine and thyroxine-binding capacity, determined by immuno-enzyme methods. Erythroid values were established in all three groups of the examined subjects. The stronger inhibition of the thyroid function in the patients with atopic asthma as compared with the cortico-dependent patients is of certain interest, in spite of the fact that the differences are not statistically significant.

Adolescent↗
PubMedDate not supplied

[Low serum thyroxin and thyroxin-binding globulin in neonatal respiratory distress (author's transl)].

Measurements of thyroxin (T4), thyroxin-binding globulin (TBG) and TSH were carried out in 34 full-term newborns, 21 prematures and 11 neonates with respiratory distress (6 with hyaline membrane disease) at 5 days of age. In cases with neonatal respiratory distress and to a lesser extent in prematures, low T4 due to a decrease of TBG was found, TSH being identical in all groups. The positive correlation between TBG and transferrin suggests a disturbance in hepatic synthesis. The authors conclude that, in cases with neonatal respiratory distress, low T4 does not mean hypothyroidism and does not require a treatment, provided TSH remains within normal limits.

Humans↗
PubMed1982

Radioimmunoassay of "free thyroxin" in dried blood spots on filter paper - preliminary observations on the effective differentiation of subjects with congenital hypothyroidism from those with subnormal thyroxin-binding globulin and normal subjects.

In this sensitive, simple method for measuring "free thyroxin" (FT4) in eluates of dried blood spots on filter paper by use of a radioimmunoassay kit (Amerlex Free T4 RIA), the measurable range of FT4 is 1.8 to 57 ng/L (equivalent to the concentration in serum), or 7 to 237 fg/tube. The mean coefficients of variation for within assay-within spots, within assay-between spots, and between assays were 5.3%, 5.0%, and 6.2%, respectively. FT4 in blood spotted on filter paper is stable for at least a month when dried and kept at either -20 degrees C, 4 degrees C, room temperature (about 25 degrees C), or 37 degrees C. The results for FT4 in dried blood spots correlated closely with the free-T4 concentration in serum (r = 0.99). The method can be used to differentiate cases of primary and secondary hypothyroidism from normal subjects and those with subnormal thyroxin-binding globulin. This method may be useful in screening for congenital hypothyroidism, because sample-retesting is not necessary.

Adolescent↗