Fluorescein in human plasma in vitro.

A method to determine fluorescein in human plasma is described. By aid of ultrafiltration a separation between fluorescein bound to plasma proteins and fluorescein free in the water is obtained. Both fractions are quantitated. Fluorescein is bound to plasma proteins. The protein binding is reversible, not sensitive to practically appearing changes in pH, temperature and gas tensions. For a normal person it appeared that at a total plasma concentration between (10(-6) - 10(-4))g . ml-1 approximately 15% was free while at a total concentration of 10(-3) g . ml-1 45% was free, pointing towards a limited amount of protein binding sites.