Albumin !

Albumin is the most abundant plasma protein: it keeps water inside vessels and carries fatty acids, bilirubin, calcium and drugs.

Updated 2026-11-01

Loading the 3D model…

Key facts

Made only by the liver; 585 amino acids in the mature form, 17 disulfide bridges, no carbohydrate; half-life ≈ 20 days.
It is ≈ 60 % of plasma protein (3.5–5 g/dL) and supplies ≈ 80 % of oncotic pressure.
Carries free fatty acids, unconjugated bilirubin, ≈ 40 % of calcium, thyroxine, haem and many acidic drugs (warfarin at site I, diazepam at site II).
A negative acute-phase reactant: it falls in inflammation, as well as in cirrhosis, nephrotic syndrome and malnutrition.

Structure 2BXD shows human albumin (chain A) with warfarin in Sudlow site I, a pocket in subdomain IIA; the highlighted active site is that pocket.
It is heart-shaped with three homologous domains (I, II, III), each with two subdomains; hydrophobic pockets hold fatty acids and drugs.

Synthesis rises with low oncotic pressure and good protein intake; it falls with inflammation (IL-6, TNF-α) and liver damage.
It is recycled by the FcRn receptor, like IgG; that is why it lasts so long in blood.

Drug–drug displacement from the same site (for example sulfonamides displacing bilirubin)
Non-enzymatic glycation in hyperglycaemia (glycated albumin, fructosamine)

Low albumin: oedema and ascites (cirrhosis), nephrotic syndrome, malnutrition, severe illness; a marker of poor prognosis.
Total calcium is corrected for albumin because part of the calcium rides on it; ionised calcium does not change.
In the newborn, drugs such as sulfonamides displace bilirubin from albumin and raise the risk of kernicterus.
The albumin-bound fraction of a drug is inactive; if albumin falls, the free fraction rises (for example phenytoin).

Think of the answer, then tap the question to see it.

Why does hypoalbuminaemia cause oedema?

Albumin supplies most of the oncotic pressure; when it falls, water leaves the capillaries for the interstitium.

What does albumin carry?

Free fatty acids, unconjugated bilirubin, calcium, thyroxine, haem and acidic drugs such as warfarin.

Why does albumin fall in a severe infection even with a healthy liver?

It is a negative acute-phase reactant: cytokines reduce its synthesis and more of it leaks into tissues.

Why do some drugs raise the risk of kernicterus in the newborn?

They displace unconjugated bilirubin from albumin; free bilirubin crosses the blood–brain barrier.

Educational information, not medical advice. For any symptom, see a health professional.

Sources: ALB: Albumin (human) (UniProt, 2026); 2BXD: Human serum albumin complexed with warfarin (RCSB Protein Data Bank, 2026); PDB-101: Molecule of the Month: Serum Albumin (RCSB Protein Data Bank (PDB-101), 2026); Albumin blood (serum) test: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake

Representative model, for educational purposes only.