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[Biochemistry](https://durgical.com/en/biochemistry/) · Protein

# 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

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## 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.

**Also called**
Human serum albumin, Serum albumin

**Genes**
ALB

**Structure (PDB)**
[2BXD](https://www.rcsb.org/structure/2BXD)

## Structure

- 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.

## Regulation

- 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.

## Inhibitors and toxins

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

## Clinical notes

- 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).

## Drugs that act here

- [Human albumin](https://durgical.com/en/pharmacology/human-albumin/)

## Related conditions

- [Cirrhosis](https://durgical.com/en/conditions/cirrhosis/)
- [Chronic kidney disease](https://durgical.com/en/conditions/chronic-kidney-disease/)
- [Neonatal jaundice](https://durgical.com/en/conditions/neonatal-jaundice/)
- [Heart failure](https://durgical.com/en/conditions/heart-failure/)

## Related

- [Plasma proteins and electrophoresis](https://durgical.com/en/biochemistry/topics/plasma-proteins-and-electrophoresis/)
- [Transthyretin (prealbumin)](https://durgical.com/en/biochemistry/enzymes/transthyretin/)
- [Bilirubin](https://durgical.com/en/biochemistry/molecules/bilirubin/)
- [Palmitate (palmitic acid)](https://durgical.com/en/biochemistry/molecules/palmitate/)
- [Immunoglobulins (antibodies)](https://durgical.com/en/biochemistry/enzymes/immunoglobulins/)

## Test yourself

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.

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

Sources: [ALB: Albumin (human)](https://www.uniprot.org/uniprotkb/P02768/entry) (UniProt, 2026); [2BXD: Human serum albumin complexed with warfarin](https://www.rcsb.org/structure/2BXD) (RCSB Protein Data Bank, 2026); [PDB-101: Molecule of the Month: Serum Albumin](https://pdb101.rcsb.org/motm/37) (RCSB Protein Data Bank (PDB-101), 2026); [Albumin blood (serum) test: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/003480.htm) (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).

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Representative model, for educational purposes only.

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