Composition and method for enrichment of white blood cells from whole human blood

A composition and method for separating red blood cells from whole blood comprising a rouleaux-forming aggregator and an enhancer for enhancing the settling rate. The enhancer is a material which alters directly or indirectly the properties of the red blood cell and may alter the structure and/or reactivity of the aggregator, without adversely affecting the morphology and function of white blood cells. In most instances, the red blood cell enhancers of the invention are osmotic agents. Such agents create a hypertonic solution while not entering the cells themselves. Preferably the enhancer is a salt of oxalic acid, a salt of malonic acid, mannitol or sucrose. Potassium oxalate is most preferred. High molecular weight substances which are large enough to form molecular bridges between red blood cells form the aggregators used in the invention. Examples of useful aggregators include dextran, hespan, pentaspan, ficoll, gum arabic, polyvinylpyrrolidone, nucleic acids, and proteins such as fibrinogen and gamma globulins.