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Chapter 072. Malnutrition and Nutritional Assessment (Part 7)

Assessment of Circulating (Visceral) Proteins The serum proteins most used to assess nutritional status include albumin, total iron-binding capacity (or transferrin), thyroxine-binding prealbumin (or transthyretin), and retinol-binding protein. Because they have differing synthesis rates and half-lives—the half-life of serum albumin is about 21 days whereas those of prealbumin and retinol-binding protein are about 2 days and 12 h, respectively—some of these proteins reflect changes in nutritional status more quickly than others. However, rapid fluctuations can also make shorter-half-life proteins less reliable. Levels of circulating proteins are influenced by their rates of synthesis and catabolism, "third spacing" (loss into interstitial spaces), and,. | Chapter 072. Malnutrition and Nutritional Assessment Part 7 Assessment of Circulating Visceral Proteins The serum proteins most used to assess nutritional status include albumin total iron-binding capacity or transferrin thyroxine-binding prealbumin or transthyretin and retinol-binding protein. Because they have differing synthesis rates and half-lives the half-life of serum albumin is about 21 days whereas those of prealbumin and retinol-binding protein are about 2 days and 12 h respectively some of these proteins reflect changes in nutritional status more quickly than others. However rapid fluctuations can also make shorter-half-life proteins less reliable. Levels of circulating proteins are influenced by their rates of synthesis and catabolism third spacing loss into interstitial spaces and in some cases external loss. Although an adequate intake of calories and protein is necessary to achieve optimal circulating protein levels serum protein levels generally do not reflect protein intake. For example a drop in the serum level of albumin or transferrin often accompanies significant physiologic stress e.g. from infection or injury and is not necessarily an indication of malnutrition or poor intake. A low serum albumin level in a burned patient with both hypermetabolism and increased dermal losses of protein may not indicate malnutrition. On the other hand adequate nutritional support of the patient s calorie and protein needs is critical for returning circulating proteins to normal levels as stress resolves. Thus low values by themselves do not define malnutrition but they often point to increased risk of malnutrition because of the hypermetabolic stress state. As long as significant physiologic stress persists serum protein levels remain low even with aggressive nutritional support. However if the levels do not rise after the underlying illness improves the patient s protein and calorie needs should be reassessed to ensure that intake is sufficient. Assessment of