EFFECT OF ASCORBIC ACID IN VIVO ON LABELING OF RED CELLS BY RADIOACTIVE SODIUM CHROMATE.

red cell mass with radioactive sodium chromate has undergone several modifications. Read' developed the technic of adding ascorbic acid in vitro to the blood-sodium chromate mixture to reduce chromate to trivalent chromium and prevent further uptake by red cells. The inhibition of chromium uptake by ascorbic acid supported the concept of Cray' that a reducing agent prevents complete tagging of erythrocytes by chromate in vivo. In 1956, Cooper et al.,4 suggested that radioactive sodium chromate could be mixed directly with blood in acid citrate dextrose (ACD ) , and that this mixture led to a higher degree of red cell labeling than when either heparin or sodium citrate alone was used. Since ACD solution did not materially re- duce the chromate ion within the first few hours of mixing, these authors added sodium chromate to the ACD solution prior to addition of whole blood. In 1957, Cunningham et al.5 stated that ACD solution does reduce chromate and that such mixtures could not be used effectively longer than 4 hours after mixing. By tracer technics and spectrophotometric analysis of mixtures of ACD and K2Cr51O4, these authors documented reduction of chromate by acid citrate dextrose formation to a chromic-citrate complex. In the course of doing clinical blood volumes we found on several occasions that the per cent of red cells labeled in vitro was decreased markedly from the approximate 90 per cent expected. Further investigation indicated that in vivo concentrations of ascorbic acid affected the labeling of human red cells in vitro.