Blood plasma fractionation

Blood plasma is the liquid component of whole blood, and makes up approximately 55% of the total blood volume. It is composed primarily of water with small amounts of minerals, salts, ions, nutrients, and proteins in solution. In whole blood, red blood cells, leukocytes, and platelets are suspended within the plasma.

Plasma contains a large variety of proteins including albumin, immunoglobulins, and clotting proteins such as fibrinogen.[1] Albumin constitutes about 60% of the total protein in plasma and is present at concentrations between 35 and 55 mg/mL.[2] It is the main contributor to osmotic pressure of the blood and it functions as a carrier molecule for molecules with low water solubility such as lipid-soluble hormones, enzymes, fatty acids, metal ions, and pharmaceutical compounds.[3] Albumin is structurally stable due to its seventeen disulfide bonds and unique in that it has the highest water solubility and the lowest isoelectric point (pI) of the plasma proteins. Due to the structural integrity of albumin it remains stable under conditions where most other proteins denature.

Many of the proteins in plasma have important therapeutic uses.[1] Albumin is commonly used to replenish and maintain blood volume after traumatic injury, during surgery, and during plasma exchange.[3] Since albumin is the most abundant protein in the plasma its use may be the most well known, but many other proteins, although present in low concentrations, can have important clinical uses.[1] See table below.[1]

When the ultimate goal of plasma processing is a purified plasma component for injection or transfusion, the plasma component must be highly pure. The first practical large-scale method of blood plasma fractionation was developed by Edwin J. Cohn during World War II. It is known as the Cohn process (or Cohn method). This process is also known as cold ethanol fractionation as it involves gradually increasing the concentration of ethanol in the solution at 5 °C and 3 °C.[3] The Cohn Process exploits differences in properties of the various plasma proteins, specifically, the high solubility and low pI of albumin. As the ethanol concentration is increased in stages from 0% to 40% the [pH] is lowered from neutral (pH ~ 7) to about 4.8, which is near the pI of albumin.[3] At each stage certain proteins are precipitated out of the solution and removed. The final precipitate is purified albumin. Several variations to this process exist, including an adapted method by Nitschmann and Kistler that uses fewer steps and replaces centrifugation and bulk freezing with filtration and diafiltration.[1][3]

Some newer methods of albumin purification add additional purification steps to the Cohn Process and its variations, while others incorporate chromatography, with some methods being purely chromatographic.[3] Chromatographic albumin processing as an alternative to the Cohn Process emerged in the early 1980s, however, it was not widely adopted until later due to the inadequate availability of large scale chromatography equipment.[3] Methods incorporating chromatography generally begin with cryodepleted plasma undergoing buffer exchange via either diafiltration or buffer exchange chromatography, to prepare the plasma for following ion exchange chromatography steps.[3] After ion exchange there are generally further chromatographic purification steps and buffer exchange.[3]

For further information see chromatography in blood processing.

In addition to the clinical uses of a variety of plasma proteins, plasma has many analytical uses. Plasma contains many biomarkers that can play a role in clinical diagnosis of diseases, and separation of plasma is a necessary step in the expansion of the human plasma proteome.

• Blood fractionation