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Serum albumin, often referred to simply as albumin is the most abundant plasma protein in humans and other mammals. Albumin is essential for maintaining the osmotic pressure needed for proper distribution of body fluids between intravascular compartments and body tissues. The human version is human serum albumin. Bovine serum albumin, or BSA, is commonly used in molecular biology laboratories.
Albumin is negatively charged. The glomerular basement membrane is also negatively charged; this prevents the filtration of albumin in the urine. In nephrotic syndrome, this property is lost, and there is more albumin loss in the urine. Nephrotic syndrome patients are given albumin to replace the lost albumin.
Because smaller animals (for example rats) function at a lower blood pressure, they need less oncotic pressure to balance this, and thus need less albumin to maintain proper fluid distribution.
Functions of albumin
- Maintains osmotic pressure
- Transports thyroid hormones
- Transports other hormones, particularly fat soluble ones
- Transports fatty acids ("free" fatty acids) to the liver
- Transports unconjugated bilirubin
- Transports many drugs
- Competitively binds calcium ions (Ca2+)
- Buffers pH
Causes of albumin deficiency (hypoalbuminemia)
- Cirrhosis of the liver (most commonly)
- Decreased production (as in starvation)
- Excess excretion by the kidneys (as in nephrotic syndrome)
- Excess loss in bowel (protein losing enteropathy)
- Mutation causing analbuminemia (very rare)
- Acute disease states (referred to as a negative acute phase protein)
Testing for albumin loss via the kidneys
In the healthy kidney, albumin's size and negative electric charge exclude is from excretion in the glomerulus. In some diseases including diabetic nephropathy, a major complication of uncontrolled diabetes. The lost albumin can be detected by a simple urine test *. Depending on the amount of albumin lost, a patient may have normal renal function, microalbuminuria, or albuminuria.
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"Serum albumin"