Plasma proteins reflect the visceral protein mass. They include albumin, transferrin, thyroxin-binding pre-albumin, and, in patients with normal kidney function, retinol-binding protein.
Serum albumin level is the most widely used measure of plasma protein in nutritional assessment, although a fall in albumin level is usually the consequence of its metabolism and reflects more the severity and duration of the metabolic stress than the nutritional status itself. Several studies have demonstrated that a serum albumin level below 30 g/l correlates with complications, but careful studies have shown it to be less predictive than clinical judgment. Sensitivity to predicting complications is better when measurements of serum albumin and transferrin are combined.
Although it is dependent on the iron status, transferrin has a better response than albumin to nutritional repletion.
Thyroxin-binding pre-albumin and retinol-binding protein, which have short half-lives, are particularly useful for following the efficacy of nutritional support. Other acute-phase reactants are markers of the injury response and its intensity rather than markers of nutritional status.
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