Albumin and Pre-Albumin
Nutrition Status & Predictor of Mortality
The most abundant plasma protein is albumin, which is synthesised in the liver and functions as a carrier for fatty acids, vitamins, minerals, bilirubin, cortisol, thyroxine and drugs. It also maintains osmotic balance between the extra and intravascular compartments of the body. Historically, albumin was used as a marker to assess protein status, since a decrease in availability of amino acids can result in the decreased synthesis of albumin. However, it is now known that specific physiological conditions can shift albumin to the extravascular space, resulting in a decrease in plasma albumin independent of overall nutritional status.
Illness, stress, inflammation, trauma and surgery all trigger this extravascular shift due to hormone and cytokine signalling. Other disease states, such as diabetes-induced glomerulosclerosis, lupus erythematosus, renal vein thrombosis, drugs, burns, cirrhosis, rheumatoid arthritis and multiple myeloma, decrease albumin levels directly. The measurement of albumin levels is also dependent on the hydration state of the patient and administration of anabolic hormones. Given the long list of physiological conditions that affect albumin, its use as a marker of nutritional status can lead to misinterpretation.
Pre-albumin (transthyretin), a carrier protein for vitamin A, is also used as a marker to identify patients at risk of malnutrition. Similar to albumin, it is a negative acute phase protein that decreases in response to metabolic stress. It has a half-life of 2 days, in contrast to the 20-day half-life of albumin. Monitoring of nutritional interventions through pre-albumin’s quick recovery has demonstrated improved treatment outcomes and has been incorporated into assessment protocols in several health-care settings. Consideration of dietary consumption, weight loss, serum proteins, wound healing and changes in medical status provide a more accurate assessment of nutritional status than reliance on serum proteins alone.