An extraction technique for the estimation of Evans blue in plasma.

The dye-dilution method for the determination of plasma volume presents several problems, one of which is the estimation of dye concentration in plasma. It is with this problem that the present paper is primarily concerned. The most frequently used dye is Evans blue, T 1824. The colorimetric estimation of this dye in plasma is open to a number of possible errors, particularly those introduced by opacity of the plasma and by the haemolysis of blood samples. Recently it has become possible quantitatively to extract Evans blue from plasma for estimation in watery solution (Allen and Orahovats, 1948; Allen, 1951 ; Korner, Morris, and Courtice, 1954; Bedwell, Patterson, and Swale, 1955). As a result of considerable experience with Korner, Morris, and Courtice's method, it has become apparent that certain details of technique are of critical importance. The purpose of this article is to describe a technique that has been found to give satisfactory results, with regard both to speed and to accuracy.