serum albumin
Meaning of serum albumin: The most abundant protein in blood, and a number that tracks how ill someone is far more reliably than how well they eat.
Definition of serum albumin
Serum albumin is the most plentiful protein in blood, manufactured by the liver. It keeps fluid inside blood vessels by exerting an inward pull, and it ferries hormones, calcium, bilirubin, fatty acids and many drugs around the body. The level is measured routinely, since it falls in liver disease, in protein loss through the kidney or gut, and in almost any serious or prolonged illness.
What does it actually do?
Two jobs, both closer to plumbing than to chemistry. The first is holding water. Protein dissolved in blood draws fluid inward across vessel walls, and albumin supplies most of that pull simply because there is more of it than of anything else. When it falls far enough, fluid seeps into the tissues and collects as swollen ankles or as fluid in the abdomen. The second job is transport. Many substances travel bound to it, including calcium, bilirubin, thyroid hormone and a long list of medicines. That binding has practical weight, because only the unbound portion of a drug is active, and a low albumin leaves more of it free to act.
Why does it fall?
| Cause | Mechanism |
|---|---|
| Inflammation or infection | The liver switches production toward other proteins |
| Liver disease | The factory itself is failing |
| Kidney disease | Protein escapes into the urine |
| Bowel disease | Protein is lost through a damaged gut lining |
| Malnutrition | Too little protein and energy supplied over a long stretch |
| Dilution | Extra fluid, from a drip or from fluid retention |
Is it a measure of nutrition?
Far less than its reputation suggests. A low level is routinely read as evidence of poor feeding, yet the commonest reason for one is illness itself. During inflammation the liver diverts production toward other proteins, small vessels leak albumin into the tissues, and the level drops within days regardless of what is eaten. Supplying more protein does not lift the number while the underlying illness continues. The measurement is genuinely useful as an indicator of how sick someone is and how they are likely to fare, which is why it appears inside several severity scores, but it is a poor guide to diet. Its slow turnover, measured in weeks rather than hours, means it also lags well behind any real change.
Also known as
Used in a sentence
Serum albumin was low, in keeping with the chronic liver disease.
Good to know
A low serum albumin usually reflects inflammation, fluid shifts or protein loss rather than diet, so it serves as a marker of illness severity rather than a measure of nutritional intake.
Word origin
Where “serum albumin” comes from
Albumin comes from the Latin albumen, egg white, itself from albus, meaning white.