Thyroid disease serum proteins

As the laboratory assessment of thyroid disease has been refined through die wide-scale availability of improved techniques and commercial kits, some confusion in terminology has developed. Table 52-1 is a review of the nomenclature for tests of thyroid hormones and thyroid-related proteins in serum. Guidehnes for the classification of various thyroid tests have been further described in a special report of the American Thyroid Association. 

The levels of transthyretin (binds to vitamin A and thyroid hormones in the blood) and serum albumin in the blood may be used as indicators of the degree of protein malnutrition. In the absence of hepatic disease, decreased levels of these proteins in the blood indicate insufficient availability of amino acids to the liver for synthesis of serum proteins. 

A serum protein of molecular weight 61 000, which migrates in front of albumin on serum protein electrophoresis. It has similar functions to albumin but it is particularly important in the binding of thyroid hormones. Low serum levels are found in a variety of conditions including malignancies and liver diseases. 

The failure of proteins to fold into their functional forms can occasionally lead to "misfolding" or "conformational" diseases.140 Many of these diseases are associated with the formation of amyloid protein, an insoluble material that is deposited as fibrils or plaques in different tissues and organs of the body. They include amyloid Ap protein as the major constituent of the plaques in Alzheimer patients, PrPc associated with neuro-degenerative diseases, a-synuclein (AS) associated with Parkinson s diseases, transthyretin (TTR) as a homotetrameric protein that is involved in the transport of thyroid hormones and retinol in human serum. In particular, the Ap protein is a peptide of 39-43 amino acids that is the... 

Abnormalities in thyroid function tests may be encountered in a variety of severe nonthyroidal illnesses, either acute or chronic, and some of the abnormalities are mediated through decreases in TBPA or in TBG, or in both binding proteins. Where the abnormality is due only to decrease in TBG and TBPA, the FTI, FTC, and similar measurements are normal but total T4 in serum is low and the resin uptake of T3 is elevated. This is the situation in chronic renal disease and although the FTI and similarly calculated free T4 factors do not give normal results in all patients, the free T4 concentration is normal in nearly all euthyroid patients (J3). 

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