Plasma chromogen and the endogenous creatinine clearance.

One of the troubles of using the endogenous creatinine clearance to measure the filtration rate is that plasma and serum contain chromogens, other than creatinine, which give a colour with the Jaffe reaction. The creatinine can, however, be isolated by adsorption on Fuller's earth (Gaebler and Keltch, 1928) and subsequently eluted with the alkaline picrate used for colour production (Borsook, 1935). This method has been used by a number of workers and its reliability established. Thus Hare and Hare (1949) found with radioactive carbon that recovery is complete, and Ralston (1955) with chromatography that no extraneous chromogen remains after treatment. But there is very little evidence as to the amounts of non-creatinine chromogen in the plasma or as to how neglect of its presence influences the creatinine clearance, and it is these points which will be considered here.