Albumin (ALB) is a nonglycosylated protein with an MW of about 66 kDa, synthesized by hepatocytes and with a half- life of about 20 days. The main functions of ALB are the maintenance of the colloidosmotic pressure, the binding and trans port of numerous endogenous and exogenous substances (metal ions, bilirubin, free fatty acids, amino acids, steroid and thyroid hormones, drugs), constituting a reserve of amino acids for protein synthesis; it also exerts an antioxidant action. ALB synthesis may decrease due to increased oncotic pressure in the liver extracellular fluid or decreased amino acid availability. In addition, ALB is a negative acute- phase protein, as its synthesis is downregulated by interleukin- 6 (IL-6). The reference values in plasma for adults, according to the IFCC international standardization (CRM 470), are 35–52 g/L.
Measurement of serum ALB is used in the evaluation of dysprotidemic states, but it should be kept in mind that the only clinically significant change is its decrease; in fact, its plasma concentration can increase only by hemoconcentration. Hypoalbuminemia may be due to the following causes:
• Decreased synthesis (liver dysfunction or protein-poor diet)
• Altered distribution between the blood compartment and extravascular spaces due to increased capillary permeability as in the case of septic shock
• Leakage into the “third space” as a result of edema or ascites
• Outward leakage, as in nephrotic syndrome, burns, or exudative enteropathy
• Inflammatory process, where ALB synthesis is decreased in favor of acute phase proteins
• Pregnancy, due to increased plasma volume
• In rare congenital disorders of albumin synthesis
In clinical practice, the measurement of serum ALB is widely used for the evaluation of liver function and situations of protein loss. The reasons for the request with the best evidences are the use in hemodialysis patients as a marker of therapeutic adequacy; in patients with MM for the staging of the disease; in patients who are candidates for human ALB replacement therapy for the calculation of the ALB dose to be administered and for the monitoring of the therapy; as a risk factor for acute renal failure (AKI) and poor prognosis after AKI.
