Half-Life of Albumin
The half-life of albumin in healthy adults is approximately 20 days (range 14-20 days). 1
Physiological Basis
Albumin's extended circulatory half-life of approximately 20 days reflects a balance between hepatic synthesis (approximately 10.5 g/day) and clearance through renal (≈6%), gastrointestinal (≈10%), and catabolic (≈84%) pathways 2
The liver synthesizes approximately 12 grams of albumin daily, representing 10% of the intravascular albumin mass, with only 40% of total body albumin located intravascularly 3
The albumin turnover time of about 25 days in normal humans is maintained through a constant fractional catabolic rate, though this rate can be modulated in disease states 2
Mechanism of Extended Half-Life
Albumin's extraordinarily long circulatory half-life results directly from its size (above the renal filtration threshold) and its interaction with the FcRn-mediated recycling pathway, which protects it from intracellular degradation 4
An intact C-terminal end of albumin (specifically the L585 residue) is required for proper FcRn binding and the full 20-day half-life; enzymatic cleavage of this terminal residue reduces the half-life dramatically to only 3.5 days 5
Clinical Implications
For Glycemic Monitoring
The 14-20 day half-life makes glycated albumin (GA) a marker of glycemic control over approximately 2-3 weeks, specifically reflecting the preceding 1-2 weeks 1
Conditions that accelerate albumin turnover (hyperthyroidism, obesity, nephrotic syndrome) falsely lower GA levels, while conditions that decrease turnover (hypothyroidism, liver cirrhosis) falsely elevate GA levels independent of glucose control 1
For Nutritional Assessment
Albumin's 20-day half-life makes it less sensitive to acute nutritional changes compared to prealbumin (half-life 2-3 days) or transferrin (half-life 8 days) 1
The long half-life means serum albumin levels reflect chronic rather than acute changes in nutritional or inflammatory status 1
Pathophysiological Alterations
In inflammatory states, the half-life of albumin shortens despite increased fractional synthesis rates, due to increased capillary permeability, expanded distribution volume, and enhanced catabolic clearance 6
The fractional catabolic rate is not completely fixed and slowly reduces when serum albumin content is markedly reduced in conditions such as protein deficiency, cirrhosis, nephrosis, and gastrointestinal diseases 3
Albumin infusion increases the fractional catabolic rate slowly, which must be considered when planning albumin substitution therapy in chronic diseases 3