Comparison of serum free thyroxine measurements by chemiluminescence and equilibrium dialysis

A study of 239 patients compared free thyroxine (FT4) measurements made by equilibrium dialysis (ED) with measurements made using the Magic Lite FT4 chemiluminescence (Cl) immunoassay (Ciba Corning Immunodiagnostics). Patient groups: 41 normals; 27 hyperthyroid; 29 hypothyroid; 37 sick euthyroid; 10 chronic renal failure (CRF) and 25 pregnant patients; 13 oestrogen; 10 heparin; 12 salicylate; and 9 dilantin-treated patients; 3 lipaemic; 5 haemolysed; 6 hyperbilirubinaemic patients; 6 low thyroid binding protein (TBP) and 6 high TBP level patients. The two assays gave comparable results in most groups. Both assays tended to give elevated values in heparinized patients but FT4–ED results were more obviously affected. Pregnant patients and women on oral oestrogen had higher mean values with FT4–ED. In both assays the sick euthyroid and CRF patients had mean FT4 values similar to healthy euthyroid patients; the range of values in sick euthyroid and CRF patients was similar in both assays but wider than in healthy euthyroid patients. A supplemental study of 81 unselected acutely ill patients using FT4–Cl alone confirmed the wider range of values to be anticipated in sick euthyroid patients.     

Vitamin A and thyroxine carrier proteins in chicken plasma: steady-state control of the plasma level of free retinol-binding protein and free thyroxine.

1. The binding parameters of prealbumin-2 with retinol-binding protein and thyroxine (T4) revealed the existence of distinct and multiple sites for both retinol-binding protein and T4. 2. From the analysis of binding parameters of retinol-binding protein with prealbumin-2 it is clear that under steady-state conditions about 99% of the holo-retinol-binding protein remains bound to prealbumin-2. 3. Equilibrium dialysis studies on binding properties of thyroid hormones with prealbumin-2 revealed that it has a single high affinity site and three low affinity sites. 4. The occurrence of three carrier proteins for thyroid hormones, thyroxine-binding globulin, prealbumin-2 and albumin has been demonstrated. However, the chicken thyroxine-binding globulin differs from human thyroxine-binding globulin by being relatively less acidic and occurring at a two-fold lower concentration. But the thyroid hormone binding parameters are comparable. 5. Highly sensitive methods were developed for determination of T4 binding capacities of the various proteins and plasma level of total T4 by fractionation of carrier proteins and further quantitatively employing in electrophoresis and equilibrium dialysis. 6. The thyroxine-binding proteins were found to be of two types, one (viz., thyroxine-binding globulin) of great affinity but of low binding capacity, which mainly acts as reservoir of T4, and another (viz., prealbumin-2) of low affinity but of high binding capacity, which can participate predominantly in the control of the free T4 pool.     

Serum free triiodothyronine to free thyroxine ratio enables early prediction of the outcome of antithyroid drug therapy in patients with Graves' hyperthyroidism.

This study scrutinizes the correlation between serum free triiodothyronine (FT3) to free thyroxine (FT4) ratios and the eventual outcome of antithyroid drug (ATD) therapy in patients with Graves' disease. Forty-four patients with Graves' thyrotoxicosis were treated with methylmercaptoimidazole (methimazole). During the follow-up, 16 patients relapsed in the short period of one to five months after cessation of the drug (relapse group), and 28 patients remained in remission when checked at 12 to 20 months after treatment (remission group). Serum FT3 to FT4 ratios [(pg/ml/ng/dl) x 10] were less than 55 throughout ATD therapy in 27 of the 28 remission patients whereas the ratios of the relapse group exceeded 55 from the early phase of methimazole treatment in 10 of 16 patients. In eight of these 10 patients the increased ratios were detected within three months of therapy (1 month, 3 patients; 2 months, 4 patients; 3 months, 1 patient). The ratios for the remaining two patients rose above 55 at the fifth and sixth months. There was no statistical difference between the remission and relapse groups in the FT3 to FT4 ratios either before nor at the completion of the treatment. However, a clear difference could be measured at a point during the therapy. Those in whom this difference was pronounced later underwent relapse.(ABSTRACT TRUNCATED AT 250 WORDS)     

Clinical evaluation of accuracy in determining serum free thyroxine and free triiodothyronine in patients with non-thyroidal illness: immunoglobulin effect on T3/TBG ratio and T4/TBG ratio

We examined the effect of endogenous immunoglobulins (G, A and M) and albumin on the measurement of thyroid hormones by different methods, including a new non-isotopic immunoassay of free thyroxine (FT4) and free triiodothyronine (FT3), in a large number of patients with non-thyroidal illness (NTI). Variations in serum protein concentrations can affect the results of radioimmunoassay of human thyroid hormones and thyroxine binding globulin (TBG). Our data revealed that in patients with non-thyroidal illness, when fluctuations in serum gamma-globulin occurred the T3/TBG and T4/TBG ratios altered. Consequently, when patients are suffering from non-thyroidal illness with changing gamma-globulin levels, clinical scientists should take care when they use T3/TBG and T4/TBG ratios as a substitute for FT3 or FT4 estimation. We found FT4 and FT3 (determined with Amerlex-M kits) T3 and the T3/TBG ratio were altered inversely due to the difference in the serum gamma-globulin levels. A recently developed enhanced luminescence enzyme immunoassay for FT3 and FT4 (Amerlite FT3 and FT4 kits) provides more reliable and accurate results, because of its resistance to interference, especially from albumin and gamma-globulin.     

Relationship between postabsorptive respiratory exchange ratio and plasma free fatty acid concentrations

The relationship between overnight postabsorptive (fasting) respiratory exchange ratio (RER) and plasma FFA concentrations was addressed using data from three separate protocols, each of which involved careful control of the antecedent diet. Protocol 1 examined the relationship between fasting RER and the previous daytime RER. In Protocol 2 fasting, RER and plasma palmitate concentrations were measured in 29 women and 31 men (body mass index <30 kg·m⁻²). Protocol 3 analyzed data from Nielsen et al. (Nielsen, S., Z. K. Guo, J. B. Albu, S. Klein, P. C. O''Brien, M. D. Jensen. 2003. Energy expenditure, sex and endogenous fuel availability in humans. J. Clin. Invest. 111: 981-988.) to understand how fasting RER and palmitate concentrations relate within individuals during four consecutive measurements. The results were as follows: 1) Fasting RER was correlated (r = 0.74, P < 0.001) with the previous day''s average RER, and less so with RER variability. 2) Fasting RER was correlated (r = −0.39, P = 0.007) with fasting plasma palmitate concentrations. 3) The pattern of the RER/palmitate relationship was similar within individuals and between individuals; a negative slope was observed significantly more often than a positive slope (χ² test; P < 0.001). Our findings suggest that, despite a fixed food quotient, the slight departures from energy equilibrium in a controlled General Clinical Research Center environment can effect plasma FFA concentrations. We suggest that including indirect calorimetry as part of FFA metabolism studies may aid in data interpretation.     

Reduced serum free thyroxine concentration in postmenopausal women receiving oestrogen treatment.

Thyroid hormone state was assessed in a group of postmenopausal women who had received long term treatment with oestrogen. Serum concentrations of total thyroxine, triiodothyronine, and thyroxine binding globulin were raised compared with those in a control group given placebo; serum concentrations of thyroid stimulating hormone did not differ between the groups. Oestrogen treatment resulted in a significant decrease in the serum free thyroxine concentration and in the ratio of thyroxine to thyroxine binding globulin, which supports the view that oestrogen is the causative factor of the physiological reduction in free thyroid hormone during pregnancy.     

Associations of body mass index and waist:hip ratio with hypertension.

Canada Fitness Survey data for people aged 20 to 69 years were analysed by means of linear discriminant analysis to determine the effect of age, weight relative to height (body mass index) and weight distribution (waist:hip ratio) on hypertension (defined as diastolic blood pressure of 90 mm Hg or more) for both sexes separately. All three variables had independent effects on hypertension, but partial correlation coefficients indicated that the contribution of waist:hip ratio was secondary to that of body mass index. The association of measurements of body fat (five skinfold measurements) with hypertension was also examined; overall these measurements gave no advantage over the more simply measured body mass index. The results confirm the importance of assessing the predominant location of body fat and the body mass index when examining excess weight in relation to disease.     

Biological treatment of phenolic wastes: Comparison between free and immobilized cell systems

Summary Phenol degradation by free and immobilized cells ofFusarium flocciferum was studied in a chemostat at steady-state conditions. For the free cell system the dilution rates varied from 0.02 to 0.13h^–1, with a total phenol removal up to 0.08h^–1. Wash-out seemed to set in at 0.11h^–1. The immobilized cells showed virtually complete phenol utilization at 1g/l, over a period of four months. At D=0.2h^–1 and above 1g/l phenol, the complete phenol removal is not achieved: a progressive increase in the outlet concentration was observed attaining a value of 284mg/l at 1.5g/l.     

Comparison of exchange of alpha-tocopherol and free cholesterol between rat plasma lipoproteins and erythrocytes.

The simultaneous exchange of (3h)tocopherol and (14C)cholesterol between rat plasma, rat plasma lipoproteins, and RBC was studied in vitro to compare quantitavely (a) the fractional exchange rates and (b) the half-times for isotope equilibration. In all incubations of RBC with plasma or with plasma lipoprotein fractions, (14C)cholesterol approached equilibrium more rapidly than (3H)tocopherol. When the RBC contained the initial radioactivity, the half-times for equilibration with plasma of cholesterol and of tocopherol were 1.0 and 2.2 hr, respectively. However, the fractional exchange rates (KRBC leads to plasma) were 0.097/hr for cholesterol and 0.188/hr for tocopherol, indicating that the RBC tocopherol pool is turning over almost twice as rapidly as the RBC cholesterol pool. The rat plasma lipoproteins were separated into five fractions by successive ultracentrifugation. Only two fractions, the high density lipoproteins (d 1.063-1.21) and the very low density lipoproteins (d is less than 1.006), participated to a significant extent in the exchange of either tocopherol or cholesterol with RBC. Cholesterol exchange between individual rat plasma lipoproteins and RBC had the same half-times for isotope equilibrium for the very low and high density lipoproteins, and the RBC fractional exchange rates were proportional to the amount of cholesterol in the lipoproteins. In tocopherol exchange between individual rat plasma lipoproteins and RBC, the very low density lipoprotein tocopherol did not equilibrate completely with the RBC. However, the initial rate of tocopherol exchange appeared to be the same for very low and high density lipoproteins. The very low density lipoproteins were disrupted by repeated freezing and thawing or by dehydrating and rehydrating, and analysis of the resulting lipoproteins indicated that free cholesterol was associated more closely than tocopherol with the phospholipid-protein portion of the molecule, which is thought to be on the surface. This difference in distribution of tocopherol and free cholesterol within very low density lipoproteins could account for their different rates of exchange and for the nonequilibrium of tocopherol between RBC and very low density lipoproteins.