Why is albumin important?

1. Binding and transport.
2. Maintenance of colloid osmotic pressure.
3. Free radical scavenging.
4. Platelet function inhibition and antithrombotic effects.
5. Effects on vascular permeability.

Binding and transport
There are actually four binding sites on albumin and these have varying specificity for different substances.
Competitive binding of drugs may occur at the same sit or at different sites (conformational changes) [eg. warfarin and diazepam].
The drugs that are important for albumin binding are: warfarin, digoxin, NSAIDS, midazolam, thiopentone.
The relevence of a low albumin and drug binding is unknown.

Osmotic pressure
Albumin is responsible for 75 - 80 % of osmotic pressure.
Starling's equation: Transcapillary Flow = k [(Pcap + p i) - (Pi + p cap )]
Remember that albumin is the main protein both in the plasma and in the interstitium and it is the COP gradient rather than the absolute plasma value that is important: this is what distinguishes hypoalbuminaemia derived from redistribution (capillary leak) from that of pure full body deficiency.

Free Radicals
Albumin is a major source of sulphydryl groups, these "thiols" scavenge free radicals (nitrogen and oxygen species).
Albumin may be an important free radical scavenger in sepsis.

Anticoagulant effects
The anticoagulant and antithrombotic effects of albumin are poorly understood this may be due to binding nitric oxide radicals inhibiting inactivation and permitting a more prolonged antiaggregatory effect.
In diabetes, glycosylated albumin may increase the incidence of thrombotic events and atherosclerosis.

Capillary Membrane Permeability
In sepsis there is an increased rate of albumin loss into the tissues - this is probably related to increased capillary membrane permeability.

Source: 4um.com