Chapter 16 Laboratory Assessment Protein, Blood: Prealbumin

Normal Values ●

15 to 36 mg/dL; 150 to 360 mg/L (SI) (5)

Nutritional Significance Prealbumin (PAB) is in a class of proteins having rapid turnover with short half-lives (2 to 3 days). PAB is also called transthyretin and thyroxine-binding prealbumin. PAB is a sensitive indicator of protein deficiency and of improvement in protein status with refeeding. When malnutrition is significant, the serum PAB will usually fall below 11 mg/dL. Serum PAB is not greatly affected by mild renal or liver disease, by fluid compartment shifts, or by clients receiving exogenous albumin. However, as renal and liver disease become more sig- nificant, the levels are decreased. In addition, iron defi- ciency does not significantly impact its level (1,7). Serum PAB increases when more than 60% of

basal energy expenditure (BEE) needs are met and decreases when less than 45% of the BEE are met or when there is no oral intake. A reasonable goal of a refeeding program in extended care is to increase serum PAB by at least 2 to 3 mg/dL in 1 week (1,7). PAB levels increase with dehydration. Corticosteroids may increase PAB levels. PAB levels decrease with (1,7): ●

overhydration ● ● ● ●

acute catabolic stress stress

infection postsurgery ● AIDS Protein, Blood: Serum Albumin

Normal Values ●

3.5 to 5 g/dL; 35 to 50 g/L (SI) (values vary depending on assay method used) (5)

Nutritional Significance

Albumin and globulin constitute most of the protein within the body and are measured as total protein. Albumin is synthesized in the liver at a rate of 8 to 14 g/d. It makes up approximately 60% of the total protein. Albumin provides about 80% of colloidal osmotic pressure of the plasma. When albumin decreases, the water in plasma moves to the interstitial compartment. The loss of plasma fluid results in hypo- volemia, which in turn triggers renal retention of water and sodium. Albumin also serves as a carrier of metals, ions, fatty acids, amino acids, metabolites, bilirubin, enzymes, hormones, and drugs (1).

● Nonnutritional factors can determine albumin

levels. Albumin level is dependent on hepatocyte func- tion. With age and declining liver function, the liver can lose its ability to synthesize albumin. Because the half-life of albumin is 12 to 21 days, significant changes in liver function specific to albumin synthesis may go undetected until after that point. Severely mal- nourished individuals have greatly decreased levels of serum albumin. However, because of its long half-life, albumin is a poor indicator of early malnutrition (1,7- 13). Approximately 50% of blood calcium is bound to protein. Thus, when serum albumin levels are low, the serum calcium levels are also low. When the serum albumin is elevated, the serum calcium is elevated (5). Albumin levels increase with dehydration (1). Albumin levels decrease with (1): ●

overhydration ● decreased absorption ➤ ➤ ● ●

pancreatic insufficiency malabsorption

inadequate intake impaired synthesis

➤ ➤ ➤ ● CHF cirrhosis acute stress increased need ➤ ● hyperthyroidism

increased loss edema ascites burns

➤ ➤ ➤ ➤ ➤ ➤ ➤ ➤ ➤

pressure ulcers hemorrhage

nephrotic syndrome Crohn’s disease sprue

Whipple’s disease

● AIDS ●

protein dilution secondary to excessive IV fluids increased capillary permeability ● increased breakdown

➤ ➤ ●

cancer trauma

infection

The following drugs may increase albumin levels (1): ●

● ● ●

anabolic steroids androgens

corticosteroids dextran

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