Direct and indirect techniques for free thyroxin compared in patients with nonthyroidal illness. II. Effect of prealbumin, albumin, and thyroxin-binding globulin.

1989 ◽  
Vol 35 (8) ◽  
pp. 1655-1662 ◽  
Author(s):  
G Csako ◽  
M H Zweig ◽  
J Glickman ◽  
M Ruddel ◽  
J Kestner
Keyword(s):  
Binding Proteins ◽  
Equilibrium Dialysis ◽  
Positive Association ◽  
Blood Collection ◽  
Free T4 ◽  
Nonthyroidal Illness ◽  
Positive Correlation ◽  
Binding Rate ◽  
One Step ◽  
Seriously Ill

Abstract We studied the correlation of thyroxin (T4)-binding proteins with the apparent free T4 (FT4) in 101 patients with nonthyroidal illness (NTI). Most patients (95%) were seriously ill at the time of blood collection. Concentrations of T4-binding prealbumin (transthyretin), albumin, and T4-binding globulin (TBG) often were low in the sera of these patients. Albumin was the most frequently subnormal, TBG the least. FT4 in serum was determined by five methods represented in 16 different assays. With few exceptions, analog (one-step) FT4 RIAs--both the binding-rate-based RIA and the related FT4 indices (calculated from triiodothyronine-macroaggregated albumin uptake and total T4)--and T4/TBG ratios correlated positively and usually highly significantly (P less than 0.01) with concentrations of prealbumin, albumin, and TBG. Equilibrium dialysis values for FT4 did not correlate with prealbumin concentrations but showed a weakly (P less than 0.03) positive association with albumin and a highly significant (P less than 0.002) positive correlation with TBG. Of the three two-step FT4 RIAs tested, the only statistically significant but weakly (P less than 0.02) positive correlation with T4-binding proteins was between Spiria FT4 and TBG. Thus, in these NTI patients, FT4 estimates vary with methodology and, to a lesser extent, with the particular assay used. The results from two-step FT4 RIAs are least associated with binding protein concentrations.

Direct and indirect techniques for free thyroxin compared in patients with nonthyroidal illness. I. Effect of free fatty acids.

1989 ◽  
Vol 35 (1) ◽  
pp. 102-109 ◽  
Author(s):  
G Csako ◽  
M H Zweig ◽  
J Glickman ◽  
J Kestner ◽  
M Ruddel
Keyword(s):  
Fatty Acids ◽  
Free Fatty Acids ◽  
Solid Phase ◽  
Equilibrium Dialysis ◽  
Free Fraction ◽  
Molar Ratio ◽  
Nonthyroidal Illness ◽  
Binding Rate ◽  
Number Of Patients ◽  
One Step

Abstract We examined the effect of endogenous free fatty acids (FFA) on the measurement of free thyroxin (FT4) by five different methodologies represented in 16 different assays in a large number of patients with nonthyroidal illness (NTI). Some, but not all, one-step (analog) FT4 RIAs negatively correlated with FFA concentration. All two-step FT4 RIAs, equilibrium dialysis FT4, and the dialyzable (free) fraction of T4 positively correlated. In contrast, a binding-rate-based FT4 RIA, FT4 indices based on T3 macroaggregated albumin uptake, and T4/TBG ratios did not correlate. We also analyzed the FT4-FFA relationship with a second, more sensitive approach by correlating test results with FFA/albumin molar ratio as an estimate of the "excess" (nonalbumin bound) FFA. We found that all FT4 RIAs, equilibrium dialysis FT4, FT4 indices based on T3 uptake, the dialyzable fraction of labeled T4 in equilibrium dialysis, the fraction of labeled T4 bound to solid phase antibody in the binding-rate-based RIA, and T3 uptake correlated with the FFA/albumin molar ratio. This FFA dependency was comparable among all the various techniques and was relatively small. Thus, increases or decreases in FT4 results due to varying FFA (and albumin) concentrations are highly likely with most currently available methods (only the T4/TBG ratio did not reveal FFA-dependency), but the magnitude of changes varies with the "excess" FFA.

Binding of labeled thyroxin analog to serum proteins evaluated after radioimmunoassay of free thyroxin.

1989 ◽  
Vol 35 (3) ◽  
pp. 475-477 ◽  
Author(s):  
G Arevalo
Keyword(s):  
Serum Proteins ◽  
Equilibrium Dialysis ◽  
Normal Serum ◽  
Thyroid Status ◽  
Nonthyroidal Illness ◽  
Serum Pool ◽  
Normal Individuals ◽  
Ambulatory Patients ◽  
One Step

Abstract In ambulatory patients, assay of free thyroxin (FT4) in serum correlates well with thyroid status and with results obtained by equilibrium dialysis. The validity of FT4 results has been questioned mainly in euthyroid patients with altered concentrations of thyroid hormone-binding proteins, as in nonthyroidal illness, hereditary analbuminemia, familial dysalbuminemic hyperthyroxinemia (FDH), and the presence of iodothyronine-binding antibodies. I present here a study of the binding of [125I]T4-derivative to serum proteins in the supernate, which is ordinarily discarded after determination of FT4 by one-step radioimmunoassay with dextran-coated charcoal used to separate the free and bound fractions. The results are expressed as a ratio, with results for a normal serum pool as reference. The average ratio was high in hyperthyroid subjects, 1.26 (SD 0.12, n = 25), and in hypoalbuminemia, 1.20 (SD 0.10, n = 15), and low in FDH, 0.62 (SD 0.11, n = 9), and hypothyroid subjects, 0.90 (SD 0.06, n = 20). In normal individuals it was 0.98 (SD 0.05, n = 30). Determination of the analog-binding rate complements the FT4 result and allows for the recognition of cases with abnormal binding by serum proteins, without recourse to other tests recommended for thyroid-function studies.

scholarly journals A Direct Free Thyroxine (T4) Immunoassay with the Characteristics of a Total T4 Immunoassay

2007 ◽  
Vol 53 (5) ◽  
pp. 911-915 ◽  
Author(s):  
Kristofer S Fritz ◽  
R Bruce Wilcox ◽  
Jerald C Nelson
Keyword(s):  
Serum Protein ◽  
Binding Proteins ◽  
Serum Proteins ◽  
Equilibrium Dialysis ◽  
Free Thyroxine ◽  
Free T4 ◽  
Serum T4 ◽  
Presence And Absence

Abstract Background: Direct free thyroxine (T4) measurements have been linked to both T4-binding serum protein concentrations and protein-bound T4 concentrations. Whether this is evidence of a relationship to total T4 concentrations has not been reported. Methods: We compared an analog-based direct free T4 immunoassay and a total T4 immunoassay. Each assay was applied to the fractions of serum T4 obtained by ultrafiltration and equilibrium dialysis. Both were applied to serum-based solutions in which free T4, T4-binding proteins, protein-bound T4, and total T4 were systematically varied, held constant, or excluded. Results: Neither the free T4 assay nor the total T4 assay detected dialyzable or ultrafilterable serum T4. Both assays detected and reported the T4 retained with serum proteins. Both free and total T4 results were related to the same total T4 concentrations in the presence and absence of T4-binding proteins. Both results were similarly related to total T4 concentrations when free T4 was held constant while total T4 was varied. Both were similarly related to a total T4 concentration that was held constant while free T4 progressively replaced protein-bound T4. These free T4 results, like total T4 results, were unresponsive to a 500-fold variation in dialyzable T4 concentrations. Conclusion: New experiments extend the characterization of a longstanding and incompletely characterized analog-based free T4 immunoassay. These free T4 measurements relate to total T4 concentrations in the same way that total T4 measurements do.

Indirect estimation of thyroid hormone-binding proteins to calculate free thyroxine index: comparison of nonisotopic methods that use labeled thyroxine ("T-uptake")

1995 ◽  
Vol 41 (1) ◽  
pp. 41-47 ◽  
Author(s):  
J D Faix ◽  
H N Rosen ◽  
F R Velazquez
Keyword(s):  
Thyroid Hormone ◽  
Binding Proteins ◽  
Free Thyroxine ◽  
Reference Ranges ◽  
Hormone Binding ◽  
Free T4 ◽  
Nonthyroidal Illness ◽  
Free Thyroxine Index ◽  
Uptake Method ◽  
Hypothyroid Patients

Abstract There are many alternative ways of estimating free thyroxine (T4) when thyrotropin screening results are abnormal. In addition to free T4 immunoassays, the menu of most automated immunoassay instruments includes a nonisotopic version of the original triiodothyronine (T3)-uptake assay called "T-uptake." We evaluated the ability of five such assays (Access, ES-300, IMx, Magnum Opus, and Stratus) to accurately estimate the free thyroxine index (FTI) in euthyroid, hyperthyroid, and hypothyroid patients with abnormal concentrations of thyroid hormone-binding proteins, and in patients with nonthyroidal illness. For comparison, we calculated a similar FTI, using either T3-uptake or direct measurement of thyroxine-binding globulin (TBG). Euthyroid reference ranges were comparable. Of euthyroid patients with increased TBG, 12-32% and 5-20% had increased or suppressed FTI, respectively, depending on the T-uptake method used. Except for IMx, 6-35% of hypothyroid patients with increased TBG had inappropriately increased FTI. Patients with nonthyroidal illness had comparable results regardless of the method used, and T-uptake methods were variably affected by known inhibitors of thyroid hormone binding. The most reliable T-uptake method appeared to be the IMx, which, despite claims that it measures all thyroid hormone-binding proteins, correlated best with TBG concentrations.

Direct and indirect techniques for free thyroxin compared in patients with nonthyroidal illness. III. Analysis of interference variables by stepwise regression

1990 ◽  
Vol 36 (4) ◽  
pp. 645-650 ◽  
Author(s):  
G Csako ◽  
M H Zweig ◽  
M Ruddel ◽  
J Glickman ◽  
J Kestner
Keyword(s):  
Stepwise Regression ◽  
Equilibrium Dialysis ◽  
Negative Relationship ◽  
Molar Ratio ◽  
Test Results ◽  
Nonthyroidal Illness ◽  
Reverse T3 ◽  
Backward Elimination ◽  
One Step ◽  
Key Variables

Abstract We applied stepwise regression for multivariate analysis of data for free thyroxin (FT4) in serum and for other laboratory tests of thyroid function in patients with nonthyroidal illness. Using the maximum R2 improvement and backward elimination methods to test five variables [prealbumin, albumin, T4-binding globulin (TBG), free fatty acids (FFA), and FFA/albumin molar ratio], we found that the variables with the greatest predictive power clustered according to the methodology of FT4 measurement. Thus, we best predicted the FT4 results obtained by 16 techniques as follows: FT4 measured by one-step (analog) RIAs, with albumin; FT4 determined by two-step (sequential) RIAs, with FFA or FFA/albumin molar ratio; FT4 estimated by a binding-rate-based RIA or conceptually related FT4 indices [based on triiodothyronine (T3) uptake], with TBG; FT4 measured by equilibrium dialysis, with TBG and FFA/albumin molar ratio; and T4/TBG ratios, with either none or prealbumin and albumin. We could very highly (P less than 0.001) predict total T4 and T3 by considering TBG, and total T3 also by considering prealbumin and albumin, whereas reverse T3 was predictable with prealbumin only (negative relationship). We found comparatively weak associations between thyrotropin (TSH) and albumin or TBG. In clinical practice, abnormalities in key variables should call attention to possible effects of these variables on FT4 and other thyroid-test results and thus to the need for appropriate correction or alternative testing.

Dependence of Free Thyroxine Estimates Obtained with Equilibrium Tracer Dialysis on the Concentration of Thyroxine-Binding Globulin

1992 ◽  
Vol 38 (7) ◽  
pp. 1294-1300 ◽  
Author(s):  
J C Nelson ◽  
R B Wilcox ◽  
M R Pandian
Keyword(s):  
Pregnant Women ◽  
Normal Control ◽  
Equilibrium Dialysis ◽  
Free Fraction ◽  
Free Thyroxine ◽  
Tracer Method ◽  
Free T4 ◽  
Nonthyroidal Illness ◽  
Thyroxine Binding Globulin ◽  
In Pregnancy

Abstract 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.

"Unbound analog" radioimmunoassays for free thyroxin measure the albumin-bound hormone fraction.

1983 ◽  
Vol 29 (7) ◽  
pp. 1408-1410 ◽  
Author(s):  
J R Stockigt ◽  
V Stevens ◽  
E L White ◽  
J W Barlow
Keyword(s):  
Human Serum Albumin ◽  
Serum Albumin ◽  
Human Serum ◽  
Equilibrium Dialysis ◽  
Human Albumin ◽  
Albumin Binding ◽  
Free T4 ◽  
One Step

Abstract We have assessed the influence of albumin-bound thyroxin (T4) on apparent free T4 values obtained by two "unbound analog" free T4 methods (AmerlexR Free T4 and Clinical Assays one-step Free T4). We evaluated sera showing three different albumin anomalies: total hereditary analbuminemia, partially corrected analbuminemia, and familial dysalbuminemic hyperthyroxinemia, where abnormal albumin-binding of analog tracer is associated with high apparent free T4 values by these methods. In hereditary analbuminemia, free T4 was almost undetectable by both assays; in contrast, free T4 by equilibrium dialysis was normal. After addition of T4-free human serum albumin, the apparent free T4 concentration in total hereditary analbuminemia became normal by the analog methods. Immunoprecipitation of [125I]T4 and the unidentified labeled kit analogs by antiserum to human albumin was negligible in untreated total hereditary analbuminemia and approximately twice normal in familial dysalbuminemic hyperthyroxinemia. Therefore, alterations in tracer binding to albumin correlate with the apparent free T4 concentrations obtained by the analog methods. The interactions of the unidentified analog tracers and T4 with albumin are such that these techniques principally reflect the albumin-bound T4 moiety.

scholarly journals Quantifying Spurious Free T4 Results Attributable to Thyroxine-Binding Proteins in Serum Dialysates and Ultrafiltrates

2007 ◽  
Vol 53 (5) ◽  
pp. 985-988 ◽  
Author(s):  
Kristofer S Fritz ◽  
R Bruce Wilcox ◽  
Jerald C Nelson
Keyword(s):  
Serum Protein ◽  
Total Protein ◽  
Binding Proteins ◽  
Serum Proteins ◽  
Equilibrium Dialysis ◽  
Free T4 ◽  
Serum Total Protein ◽  
Semipermeable Membranes ◽  
Serum Free ◽  
Thyroxine Binding Globulin

Abstract Background: Direct equilibrium dialysis and direct ultrafiltration free thyroxine (T4) assays rely on semipermeable membranes to exclude T4-binding serum proteins from dialysates and ultrafiltrates. The presence of these proteins in dialysates or ultrafiltrates will yield spuriously high free T4 values when free T4 is quantified by RIA. Methods: We used a nonanalog free T4 RIA that detects and quantifies dialyzable and ultrafilterable serum free T4 to detect T4-binding serum proteins. Two equilibrium dialysis devices and 3 ultrafiltration devices were used to illustrate this application. Displacements of [125I]T4 from anti-T4 by various concentrations of T4-depleted thyroxine-binding globulin, albumin, and serum total protein were compared to displacements by various concentrations of free T4. Results: Both dialysis devices excluded detectable T4-binding serum proteins from dialysates. Two of 3 ultrafiltration devices excluded detectable T4-binding serum proteins from ultrafiltrates. One did not, and its ultrafiltrate yielded spurious free T4 values that correlated directly with serum protein concentrations. Conclusion: The presence or absence of T4-binding proteins in dialysates and ultrafiltrates and the spurious free T4 values that these proteins cause can be documented using a nonanalog free T4 RIA.

Meaning of serum free-thyroxin values in nonthyroidal illnesses: seven methods compared.

1983 ◽  
Vol 29 (12) ◽  
pp. 2091-2093 ◽  
Author(s):  
D W Chan ◽  
J M Waud ◽  
E Taylor ◽  
J Stem ◽  
H Drew ◽  
...  
Keyword(s):  
Enzyme Inhibitor ◽  
Equilibrium Dialysis ◽  
The Other ◽  
Free T4 ◽  
Serum Free ◽  
One Step ◽  
Dialysis Method

Abstract Serum free thyroxin (FT4) was determined in 40 patients with various nonthyroidal illnesses. We studied seven methods: (1) a free thyroxin index calculated from total T4 and triiodothyronine resin uptake; (2) a free T4 index determined by enzyme inhibitor assays (Abbott's "Tetrazyme" and "Thyrozyme"); (3) a free T4 index calculated from total T4 and thyroxin-binding globulin; (4) free T4 by equilibrium dialysis; (5) Amersham's free T4 RIA; (6) Clinical Assays' one-step free T4 RIA; and (7) Clinical Assays' two-step free T4 RIA. Approximately half of the free T4 results were in the euthyroid range and the other half in the hypothyroid range by methods 1, 2, 5, and 6. Results for free T4 by methods 3 and 7 were similar to those by equilibrium dialysis (method 4), the percentages of patients with results in the euthyroid range being 68%, 65%, and 76%, respectively.

On the albumin-dependence of measurements of free thyroxin. II. Patients with non-thyroidal illness.

1987 ◽  
Vol 33 (1) ◽  
pp. 87-92 ◽  
Author(s):  
G Csako ◽  
M H Zweig ◽  
C Benson ◽  
M Ruddel
Keyword(s):  
Serum Albumin ◽  
Binding Proteins ◽  
Equilibrium Dialysis ◽  
Poor Performance ◽  
Albumin Concentration ◽  
Low T3 Syndrome ◽  
Low T3 ◽  
One Step ◽  
The One

Abstract We studied the relation between thyroxin-binding proteins and free thyroxin (FT4) measurements by five radioimmunoassays (RIA) and an FT4 index (FT4I) in patients with non-thyroidal illness (NTI). The one-step FT4 RIAs and the FT4I frequently failed to identify the true FT4 status (as determined by equilibrium dialysis) of NTI patients. In these patients, falsely low FT4 results with one-step RIAs and FT4I were associated with decreasing total T3 and T4 concentrations, which, furthermore, paralleled decreasing serum albumin concentrations. All NTI patients with "low T3, low T4 syndrome" had subnormal albumin concentration. The two-step RIAs and equilibrium dialysis showed normal FT4 concentrations in most patients with NTI. However, sera from a subset of NTI patients with "low T3 syndrome" gave above-normal FT4 results with these methods. From their predictably poor performance in the presence of a subnormal albumin concentration, we conclude that the one-step FT4 RIAs and FT4I are inappropriate for testing the thyrometabolic status of NTI patients.

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