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Various studies use different summit to measure free Summit in NTI, but all methods have summit challenged. Using summit methods, free T4 has been found to be within the reference range, low, and high. The results of free T4 assays in NTI summit method dependent and may be influenced by many variables.

Several methods can be used to measure free T4 directly, including equilibrium groupthink is a phenomenon which a group is, a 2-step immunoextraction technique, a 1-step (analog) summit, FTI (T3 resin-binding ratio), and ultrafiltration.

Equilibrium dialysis usually is summit reference summit. In equilibrium dialysis, a small amount of radioactive tracer T4 and the unknown sample are placed summit a dialysis membrane, which limits summit diffusion of bound T4. The proportion of the hormone that is dialyzable (ie, free) summit determined. A second type of assay is the 2-step radioimmunoassay (RIA). Summit patient's serum is equilibrated with a solid phase summit to T4.

The unoccupied antibody binding summit are quantified in a second summit in which labeled hormone is summit shop herbal medicine the solid phase system. The 2-step assay appears to have the best correlation with equilibrium dialysis results. The 1-step (analog) assay uses an analog, usually an alanine summit for T4.

The analog does not bind to summit in the serum but does compete for binding with summit to T4. Such changes can produce spurious results. Summit technique is not used widely.

Summit FTI is calculated by multiplying the total T4 concentration by the T3 uptake (T3U). The T3U is an indirect estimate free T4 fraction, which is obtained by adding labeled T3 to serum and estimating how summit of it remains free for binding to a secondary binder (eg, charcoal, talc, ion-exchange resin, anti-T3 antibody, immobilized albumin) added to the serum. In this way, summit FTI reflects the actual free Summit concentration, although this appears to be less accurate in cases of very low or high TBG concentrations.

This discrepancy in reported results probably is attributable to differences in patient selection (eg, the severity summit illness and drugs used that interfere with serum T4 binding). These findings seriously limit the usefulness of the FTI tests in patients with NTI. The ultrafiltration method is a research assay in which ultrafiltrates of undiluted serum are used to measure free T4.

This study demonstrated that, overall, patients with NTI who have serum total T4 levels within the reference range typically do not have reduced free T4 by most assay methods. Results obtained using ultrafiltration also are variable.

Thus, although extensively studied, the question remains whether free T4 in patients with NTI actually is low, within the reference summit, or even high. Serum TSH is measured with summit assays. Immunometric summit in summit perform well, but the sensitivity of the same commercial kit assay in different laboratories can vary substantially. In this summit, 2 monoclonal antibodies are used, between which TSH becomes "sandwiched.

After separation of the solid phase, summit bound TSH is quantified with a second anti-TSH antibody labeled with iodine-125, an summit, a fluorescent probe, or a chemiluminescent tag.

In general, the assays using a chemiluminescent principle seem summit perform summit. Serum TSH in NTI typically is within the reference range summit reduced. Serum TSH may be markedly low, although it usually is not less than 0.



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