Blood plasma sample preparation method for the assessment of thyroid hormone-disrupting potency in effect-directed analysis.

A sample preparation method combining solid-phase extraction (SPE) and liquid-liquid extraction (LLE) was developed to be used in Effect-Directed Analysis (EDA) of blood plasma. Until now such a method was not available. It can be used for extraction of a broad range of thyroid hormone (TH)-disruptors from plasma with high recoveries. Validation of the method using spiked cow plasma showed good recoveries for hydroxylated polybrominated diphenyl ethers (OH-PBDEs; 93.8 ± 19.5%), hydroxylated polychlorinated biphenyls (OH-PCBs; 93.8 ± 15.5%), other halogenated phenols (OHPs; 107 ± 8.1%), and for short-chain (<8 C-atoms) perfluoroalkyl substances (PFASs; 85.2 ± 24.6%). In the same extracts, the potency of the compound classes spiked to the cow plasma to competitively bind to transthyretin (TTR) was recovered by 84.9 ± 8.8%. Furthermore, the SPE-LLE method efficiently removed endogenous THs from the extracts, thereby eliminating their possible contribution to the binding assay response. The SPE-LLE method was applied to polar bear plasma samples to investigate its applicability in future EDA studies focusing on TH-disrupting compounds in this top predator species that is exposed to relatively high levels of bioaccumulating pollutants. A first screening revealed TTR-binding potency in the polar bear plasma extracts, which could be explained for 60-85% by the presence of OH-PCBs.

Therapeutic drug monitoring during pregnancy and lactation: thyroid function assessment in pregnancy-challenges and solutions.

The diagnosis and monitoring of thyroid disease necessitates the knowledge of thyroid pathophysiology and of the technical limitations of current thyroid-related biochemical tests. Thyroid disease diagnosis and monitoring are further complicated during pregnancy and lactation, due to pregnancy-related changes in thyroid hormone metabolism. Dramatic changes that occur in thyroxine and triiodothyronine ranges during pregnancy pose challenges for hypothyroid gravidas. Very early in pregnancy, levothyroxine replacement needs to be increased. Moreover, increases in thyroid hormone replacement need to be conducted individually and on a timely basis. For reasons that are still not entirely clear, although dependent in part on changes in thyroxine binding, free thyroxine (FT4) levels decrease as pregnancy progresses necessitating the use of trimester-specific reference intervals for appropriate replacement. Thyroxine binding protein levels vary by hormonal status, inheritance, and disease states and are higher in pregnancy; hence, FT4 assays became popular because they measure the unbound hormone. However, current FT4 immunoassays are estimate tests that do not reliably measure FT4 and are known to be sensitive to alterations in binding proteins and therefore are method-specific. The need to reliably identify hypothyroxinemic pregnant patients, especially in the first trimester, is of prime importance for early fetal brain development before the fetal thyroid functions. This article addresses 1) the current limitations of laboratory-free thyroxine immunoassay methodologies and especially during pregnancy; 2) trimester-specific reference intervals for thyroid function tests; and 3) the study of levothyroxine pharmacokinetics in pregnant and nonpregnant women.

Impact of thyroxine-binding globulin on thyroid hormone economy during pregnancy.

Pregnancy-associated changes in thyroid hormone economy are well-established and are of significant clinical relevance to women with established hypothyroidism because they usually result in increased thyroxine dose requirements by these women. Studies suggest that elevations in serum thyroxine-binding globulin (TBG) have the most influence on this increased need for thyroxine, although the exact contributions by TBG rises and by other mechanisms is as yet unclear. We report the case of a 42-year-old woman, with both established primary hypothyroidism and TBG deficiency, who we have now managed through two full-term pregnancies. The patient was noted to have a baseline TBG that was approximately 30% of the average baseline level reported for non-TBG-deficient individuals. Her TBG levels were induced by pregnancy, although the absolute increase of 1.0 mg/dL was only half the increase usually associated with pregnancy. Despite the patient's low baseline TBG level and her blunted pregnancy-associated TBG induction, her absolute and relative pregnancy-associated increases in thyroxine replacement dosage mirrored those found in non-TBG-deficient, hypothyroid women. Thus, our limited study suggests that an increase in TBG concentration is not the key determinant for the increase in thyroxine requirement in pregnancy.

Serum thyroxine binding capacity-dependent bias in five free thyroxine immunoassays: assessment with serum dilution experiments and impact on diagnostic performance.

OBJECTIVES: To assess the presence and magnitude of a serum thyroxine binding capacity (sBC)-dependent bias in five free thyroxine (FT(4)) immunoassays, compared with equilibrium dialysis (ED). The exhibited bias is confronted with clinical results from previous studies to evaluate its impact on FT(4) determination in sera with various sBC. DESIGN AND METHODS: The sera of three pregnant women and three non thyroidal ill (NTI) patients were serially diluted in an inert buffer to progressively decrease the sBC. FT(4) values were measured in diluted and undiluted samples with the six assays. RESULTS: As a function of increasing dilution performed on pregnancy sera, except for ED and Vitros ECi FT(4,) the other four FT(4) assay results decreased to different degrees, in the following order: two-step GammaCoat RIA< Elecsys< ADVIA:Centaur< Amerlex-MAB RIA. In sera from NTI patients, the decrease was more marked and found at high dilution with the Vitros ECi assay. Data from previous studies showed that FT(4) measured with biased assays were decreased only in samples from very severely NTI patients with low sBC and that FT(4) results in pregnancy sera with high sBC were not significantly biased. CONCLUSIONS: The dilution test is a sensitive alarm to assess sBC-dependent bias in FT(4) assays. For all FT4 assays and particularly when a bias is observed, documentation should be sought on the diagnostic performance of the assay and supported by a detailed clinical study including samples with low sBC. Physicians should still be educated about the limitations of FT(4) assays.

The effect of double filtration plasmapheresis on thyroid hormone economy and thyroid function.

Five cases of rheumatoid arthritis (RA), two cases of systemic lupus erythematosus (SLE), a case of mixed connective tissue disease (MCTD), and a case of cold urticaria were treated with double filtration plasmapheresis (DFP). Each aliquot of plasma was obtained at three different points of the DEP circuit during the treatment and concentrations of thyroid hormones as well as thyroxine binding globulin (TBG) were measured. Despite the removal of considerable amounts of triiodothyronine (T3), thyroxine (T4), and TBG from the plasma, levels of plasma free T3 (FT3) and free T4 (FT4) before and immediately after DFP treatment were not significantly different. These results indicate that DEP therapy rarely affects plasma concentration of active thyroid hormones in patients who undergo such therapy.

[Assessment of nutritional status for surgical planning]. / Die Erfassung des Ernährungszustands zur Operationsplanung.

72 patients with gastro-intestinal carcinomas were involved in a retrospective study in which 97 metabolic parameters were pre-operatively determined from each of them and subsequently tested by stepwise discriminant analysis for their bearings on clinical mortality. A discriminant function of seven parameters was obtained and can be used as a prognostic nutritional index for successful subdivision of patients into differentiated risk groups. Two prospective control studies were conducted into 605 patients consecutively operated on for benign and malignant diseases for the purpose of testing the nutritional index for its prognostic information potential. The discriminant function proved to be applicable to differentiation between patients with high, moderate, and low surgical risk. Findings were unambiguous. The nutritional index can thus be used as an aid for decision-making in cases in which alternatives exist between several surgical approaches. The importance of malnutrition as a possible causative factor of complications is likely to grow along with the invasiveness of the intervention.

Post-natal thyroid function in low birth weight infants; a longitudinal assessment of free thyroxine and thyroid hormone binding globulin.

Because the concentrations of serum free thyroxine (FT4) and thyroid hormone binding globulin (TBG) have not been fully evaluated in preterm infants at the immediate post-natal period, we studied the longitudinal changes of serum FT4 and TBG, along with thyroxine (T4) and thyroid stimulating hormone (TSH), at birth (cord blood), 2 days, 1 week and 2 weeks of age in 7 infants with birth body weight less than or equal to 1000 g, 7 infants with body weight 1001 to 1350 g, 11 infants with body weight 1351 to 2499 g, and 11 full-term infants. Free T4 concentrations were measured by Corning Medical radioimmunoassay (RIA) kit. The infants with extremely low birth weight (ELBW) (body weight less than or equal to 1000 g) showed precipitous declines of total T4 and, to a lesser extent, of FT4 concentrations at 1 and 2 weeks of age. These post-natal T4 and FT4 decreases in ELBW neonates have not previously been reported. The clinical significance of this finding remains, speculative, but it may be due to metabolic or nutritional problems related to extreme prematurity itself. This study suggests that measurement of FT4 is a useful adjunct to the assessment of ELBW infants with very low T4 values, if done between 1 to 2 weeks of age, and could be used as a primary hypothyroid screening tool instead of T4 measurements, provided that an FT4 assay is developed that uses the elute of blood spotted on filter paper.

Subclinical protein malnutrition in irritable bowel syndrome: assessment by retinol-binding protein (RBP) and thyroxine-binding pre-albumin (TBPA).

We have assessed the nutritional status of 31 patients with irritable bowel syndrome (IBS) and 75 control subjects by anthropometry (height, weight, mid-arm circumference, biceps, triceps and subscapular skinfolds) and three plasma proteins: albumin, retinol-binding protein (RBP), and thyroxine-binding pre-albumin (TBPA). There was no significant difference between the patients and controls for any of the anthropometric measurements, but mean (+/- s.d.) plasma concentrations of RBP and TBPA were significantly lower in patients with IBS, 7.21 +/- 2.77 mg/dl (P less than 0.01); and 26.57 +/- 7.33 mg/dl, (P less than 0.001) respectively than in the control group, 8.85 +/- 2.56 mg/dl and 32.71 +/- 6.30 mg/dl. We conclude that patients with IBS may have subclinical protein deficiency in the absence of demonstrable organic bowel disease.

Ratio of thyroxine to thyroxine-binding globulin. An assessment of the validity of a single reference range.

The thyroxine:thyroxine-binding globulin ratio in serum (T4:TBG) has been proposed as a measure of thyroid status unaffected by altered binding protein levels. Here 320 apparently euthyroid patients are used to derive euthyroid ranges for serum thyroxine concentrations at specific TBG levels. These ranges are compared with those predicted by a T4:TBG reference range derived from the same patient data. The comparison suggests that the ratio would give false positives for hyperthyroidism at low TBG levels and false negatives at high TBG levels. To overcome this the use of graphical reporting of results or the relation of patient results to empirical reference ranges appropriate to the TBG level is suggested.

[Measurement for serum thyroxine-binding globulin (TBG) and its clinical assessment in diagnosis of thyroid states (author's transl)].

Serum levels of thyroxine (T4)-binding globulin (TBG) were determined by a radioimmunoassay using cellulose-linked antibody to TBG. Values obtained in healthy young adults averaged 1.62 +/- 0.25 (SD) mg/100 ml, and no significant difference wwas detected between males and females. The TBG levels remained within the normal limit in hyperthyroidism while they were significantly increased in hypothyroidism. Interestingly enough, TBG levels were significantly elevated in chronic thyroidities with no overt hypothyroidism. In normal pregnancy, TBG was increased slightly in the first trimester, and markedly in the second and third trimesters. In one case of congenital TBG deficiency, no immunoreactive TBG was detected. It was demonstrated, further, that an inverse relationship (r = -0.7593) existed between the TBG level and serum triiodothyronine uptake index, and that a direct relation (r = +0.6557) was present between the TBG level and T4 in sera from normal subjects and pregnancy. Ratios of T4/TBG were markedly increased in hyperthyroidism, and decreased in hypothyroidism, showing no overlap with the normal subjects, whereas they were below the normal limit in half the cases in the second and third trimesters of pregnancy. The radioimmunoassay for TBG was useful in evaluating hypothyroid states, because it could differentiate the increase in T4 associated with elevated TBG from hyperthyroidism.

Albumin, transferrin and the thyroxine-binding prealbumin/retinol-binding protein (TBPA-RBP) complex in assessment of malnutrition.

A comparative study of the level of 4 plasma proteins in malnutrition shows that albumin has low sensitivity, transferrin has intermediate and the TBPA-RBP complex has the highes sensitivity to an alteration in the nutritional status. According to protein and/or iron deficiency, the synthesis of trnasferrin seems to be submitted to contradictory impulses which partially invalidates this test as a reliable index for estimating protein depletion alone. On the contrary, the components of the TBPA-RBP complex respond together and in a parallel direction to protein deficiency. The high degree of sensitivity of TBPA and RBP to an inadequate protein intake is apparently related to their rapid turnover rate and to their unusual richness in tryptophan, which is known to play a key role in the control of protein synthesis. Measurement of TBPA (or RBP) is proposed as a method for the detection of pre-kwashiorkor and early marasmus.