What is the half-life of albumin?

• A. 3 days
• B. 8 days
• C. 12 days
• D. 20 days

Answer: (D)

Albumin turns over slowly in the circulation. Half-life is the time it takes for the amount present to drop to half its value, and for albumin this turnover is quite gradual because it is a large plasma protein synthesized mainly by the liver and it moves between the intravascular space and tissues before being broken down. In adults, the half-life of albumin is about twenty days, with a typical range around 17–21 days. This long half-life means albumin levels reflect longer-term protein status rather than rapid changes, which is why it’s not a good marker for short-term nutritional adequacy.