Transthyretin half-life

PEM is frequently associated with changes in serum markers such as protein, lipid, and nitrogen (Hendrickse, 1991). Decreased serum albumin levels have been used as a standard PEM indicator. Since albumin has a long half-life of 18 days in the plasma and a large pool size that decreases in various illnesses (such as hepatic insufficiency and nephrosis), it is not a specific marker for recent nutritional inadequacies. Prealbumin (or transthyretin), by virtue of its higher catabolic rate (half-life = 1.9 days) and small pool size, is a very sensitive and fairly specific indicator of acute malnutrition and shortterm responses to nutritional replacements in patients of all ages (Bernstein and Ingenbleek, 2002). 

Transthyretin levels are often used as an indicator of protein status because of its relatively short half-life, a high tryptophan content, a high proportion of essential-to-nonessential amino acids, and small pool size. However, it is a negative APR. Levels fall in inflammation and malignancy and in cirrhosis of the liver and protein-losing diseases of the gut or kidneys. Therefore a sensitive acute phase reactant, such as CRP, should always be assayed along with TTR if levels are to be used to estimate nutritional status. History and physical examination are also important aspects of such evaluations. ... 

In clinical practice, only a few laboratory tests are of value in tlie assessment of protein-energy status It is particularly important to recognize that serum protein concentrations are not helpful in sick patients with any form of inflammatory process (see Chapter 20). Although serum albumin is often measured and reported as an indicator of protein-energy status, factors such as increased transcapillary escape and reduced hepatic synthesis malce it of little value as a nutritional marker. Serum albumin is, however, a valuable prognostic marker and is frequently used as part of prognostic indices. Short half-life proteins, such as transthyretin (prealbumin) also may be of some limited value in patients with no inflammatory response. 

Transthyretin (also known as prealbumin) Liver plasma circulating form is a tetramer composed of four identical monomers. M.W. 55,000 1-2 days N 20-40 mg/dl Mild 10-15 mg/dl Moderate 5-10 mg/dl Severe <5 mg/dl Circulates in plasma in a 1 1 complex with retinol-binding protein, transports thyroxine, has a small body pool, and has a short half-life. Sensitive indicator of protein deficiency and in the improvement with protein refeeding. 

LBM includes skeletal muscle, somatic protein, and functional proteins such as circulating proteins and the visceral proteins. Biochemically, LBM can be assessed by measuring the serum visceral proteins, albumin (ALB), transferrin (TFN), and prealbumin (thyroxine-binding prealbumin or transthyretin). Other serum proteins, such as retinol-binding protein, flbronectin (an opsonic protein), and somatomedin-C (insulin-like growth factor-1), that have a very short half-life (less than 12 to 24 hours), have been suggested as... 

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