Serum Prealbumin: Is It a Marker of Nutritional Status Or of Risk of Malnutrition?(Editorial‪)‬

Hospitalized patients who are undernourished are more likely to develop clinical complications and have relatively poor outcomes, with increased length of stay (LOS) [1] and higher mortality compared with well-nourished patients. Provision of adequate nutritional support reduces the complication rate and improves outcome (1). Considerable efforts have therefore been made to identify patients at risk of malnutrition, with a view to early provision of nutritional support. A full nutritional assessment is a complex process, involving detailed assessment of nutritional intake, changes in body composition, signs or symptoms of nutritional deficiency or excess, and laboratory tests, and it should include not only protein-energy status but also vitamins and essential trace elements. Because of this complexity, rapid screening tests have been sought to identify patients who may already be malnourished or are at risk of malnutrition, who can then undergo a more detailed nutritional assessment. The screening tools with the most validation for protein-energy malnutrition include body mass index (weight/ [height.sup.2]) in conjunction with recent changes in weight and a simple assessment of illness severity (2). In many patients, however, obtaining an accurate measurement of current and previous weight to allow calculation of rate of weight loss may not be possible, so clinicians have sought a rapid, reliable laboratory method, usually involving plasma proteins, to obtain comparable information. Serum albumin is of virtually no value in assessment or monitoring of nutritional status (3) but is mentioned here because, surprisingly, there still remain some clinicians who use it as part of their nutritional assessment. The main factor affecting plasma albumin concentration in patients is the rate of transcapillary escape into the interstitial fluid. This transcapillary escape of albumin is markedly increased in disease [as part of the systemic inflammatory response syndrome (SIRS)], leading to decreased plasma albumin concentrations (4). It is inevitable that postoperative patients and patients with severe infection will have low plasma albumin concentrations. The more severe the disease, the lower the albumin, and therefore the lower the albumin, the worse the prognosis. Prealbumin, also known as transthyretin, has a half-life In plasma of ~2 days, much shorter than that of albumin. Prealbumin is therefore more sensitive to changes in protein-energy status than albumin, and its concentration closely reflects recent dietary intake rather than overall nutritional status (5). Because of this short half-life, however, the concentration of prealbumin falls rapidly as a result of the fall in its synthetic rate when there is a reprioritization of synthesis toward acute-phase proteins such as C-reactive protein (CRP), fibrinogen, or al-acid glycoprotein. Moreover, prealbumin concentration in plasma, like that of albumin, is affected by changes in transcapillary escape. Hence, interpretation of plasma prealbumin is difficult in patients with infections, inflammation, or recent trauma (4). Despite this difficulty, interest in prealbumin as a potential marker of nutritional status in certain groups of patients led to the First International Congress on Transthyretin in Health and Disease in 2002 (6).