Cohnfraktioneringen

Cohnfraktioneringen, or Cohn fractionation, is a method for separating proteins in human blood plasma by sequential precipitation with ethanol at cold temperatures. Developed in the 1940s by the American biochemist Edwin J. Cohn and colleagues, the process was designed to produce therapeutic plasma fractions on a large scale and to meet wartime needs for plasma-derived medicines.

The technique relies on carefully controlled conditions of ethanol concentration, temperature, pH, and ionic strength to cause different plasma proteins to precipitate at different steps. The process typically yields a series of fractions, traditionally labeled I through VII, with each fraction enriched for specific groups of proteins. In general terms, albumin, immunoglobulins, fibrinogen, and various clotting factors are separated into distinct fractions, allowing the production of targeted plasma products.

Historically, Cohn fractionation became the backbone of plasma-derived therapeutics in the mid-20th century, enabling widespread production of albumin, gamma globulins, and coagulation-factor concentrates. It contributed to advances in medicine and emergency care, especially in resource-limited or wartime settings. Over time, many laboratories shifted to chromatography-based methods and other modern purification techniques that offer greater specificity, higher yield, and improved safety. Nevertheless, Cohn fractionation remains a foundational concept in the field of plasma protein processing and influenced subsequent developments in plasma fractionation, quality control, and product safety standards. Some contemporary processes still employ ethanol precipitation as part of hybrid or legacy workflows.