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Albumin

Albumin comprises 60% of the total serum protein and 60 to 80% of colloid osmotic pressure. Serum albumin is synthesized solely by the liver and has several physiological functions: transport of low molecular weight substances such as calcium, hormones, and drugs; binding of toxic heavy metal ions; maintenance of colloid osmotic pressure; and provision of a protein reserve. Normally, about 4% of the total body albumin is replenished each day. The rate of production is dependent on the supply of amino acids, plasma oncotic pressure, inhibitory cytokine (especially IL-6) concentration, and the number of functioning hepatocytes. Circulating half-life of plasma albumin is 19 to 21 days.

Plasma albumin levels are low in neonates, typically between 2.8 and 4.4 g/dL. Adult levels are reached after the first week of life. Levels are slightly higher in children (4.5 – 5.5 g/dL) between the age of 6 years and young adulthood. Thereafter, levels decline to typical adult levels. Albumin levels show a downward trend throughout pregnancy and with aging, especially after age 70. Serum albumin levels are normally lower in hospitalized than ambulatory patients. Albumin levels can decrease as much as 1 g/dL after a patient becomes recumbent. Albumin concentration may decrease after crystalloid infusion or in patients with fluid retention. Falsely low values will be obtained if a blood sample is drawn above an IV site.

Hypoalbuminemia can be caused by many different disease states. The main causes include:

  • Protein loss (nephrotic syndrome, burns, protein losing enteropathy)
  • Transcapillary leak into the interstitial fluid
  • Chronic liver disease

Plasma albumin is seldom decreased in acute hepatitis, because of its long circulating half-life. Decreased serum albumin usually indicates liver disease of more than 3 weeks duration. Albumin is a good indicator of decompensation and prognosis in cirrhosis.

Plasma albumin is of virtually no value in assessment or monitoring of nutritional status. The primary cause of decreasing plasma albumin concentration in sick hospitalized patients is transcapillary escape into the interstitial fluid as a result of the systemic inflammatory response syndrome (SIRS). Postoperative patients and patients with severe infection inevitably have low plasma albumin. The more severe the disease is, the lower the albumin, and therefore the lower the albumin, the worse the prognosis. Hypo-albuminemia is associated with poor surgical outcome and increased length of stay. Serum albumin levels less than 2 g/dL are associated with a 60% thirty-day mortality rate.

Abnormally high albumin levels are seldom clinically important. Increased serum albumin levels are seen only with dehydration or after excessive albumin infusion. Artefactual causes of high levels include specimen evaporation and prolonged use of a tourniquet during venipuncture.

Reference range is 3.5 – 5.0 gm/dL.

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