Albumin is a carbohydrate‑free protein, which constitutes 55‑65 % of total plasma protein. It maintains oncotic plasma pressure, and is also involved in the transport and storage of a wide variety of ligands and is a source of endogenous amino acids. Albumin binds and solubilizes various compounds, e. g. bilirubin, calcium and long-chain fatty acids. Furthermore albumin is capable of binding toxic heavy metal ions as well as numerous pharmaceuticals, which is the reason why lower albumin concentrations in blood have a significant effect on pharmacokinetics.
Hyperalbuminemia is of little diagnostic significance except in the case of dehydration. Hypoalbuminemia occurs during many illnesses and is caused by several factors: compromised synthesis due either to liver disease or as a consequence of reduced protein uptake; elevated catabolism due to tissue damage (severe burns) or inflammation; malabsorption of amino acids (Crohn’s disease); proteinuria as a consequence of nephrotic syndrome; protein loss via the stool (neoplastic disease). In severe cases of hypoalbuminemia, the maximum albumin concentration of plasma is 2.5 g/dL. Due to the low osmotic pressure of the plasma, water permeates through blood capillaries into tissue (edema). The determination of albumin allows monitoring of a controlled patient dietary supplementation and serves also as an excellent test of liver function.
Reference intervals according to Tietz
| 0-4 days | 2.8-4.4 g/dL | 28-44 g/L | 421-662 µmol/L |
| 4 days-14 years | 3.8-5.4 g/dL | 38-54 g/L | 572-812 µmol/L |
| 14-18 years | 3.2-4.5 g/dL | 32-45 g/L | 481-677 µmol/L |
| 18-60 years | 3.5-5.2 g/dL | 35-52 g/L | 527-782 µmol/L |
| 60-90 years | 3.2-4.6 g/dL | 32-46 g/L | 481-692 µmol/L |
| >90 years | 2.9-4.5 g/dL | 29-45 g/L | 436-677 µmol/L |
| millimole per liter | mmol/L = mM/L = millimol/L |
| micromole per liter | µmol/L = mcmol/L = umol/L = µM/L = mcM/L = uM/L = micromol/L |
| gram per liter | g/L = gram/L |
| gram per deciliter | g/dL = gram/dL |
| gram per 100 milliliters | g/100mL = gram/100mL |
| gram percent | g% = gram% |
| milligram per milliliter | mg/mL = millig/mL = milligram/mL |