Cholesterol Measurement in Serum and in Plasma

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Abstract
The effect on the plasma cholesterol concentration of various anticoagulants added to the blood in dry form, as compared with that of serum, has been studied. The amounts of anticoagulants used, per 5 ml. of blood, were: heparin, 2.5 mg.; oxalate mixture, 12 mg.; tetrasodium EDTA, 5 mg.; sodium oxalate, 12mg.; and ACD mixture, 5.3 mg. citric acid, 15.8 mg. Na citrate, and 17.6 mg. dextrose. All these anticoagulants caused a decrease in the plasma cholesterol concentration. The mean cholesterol decrease (serum minus plasma) produced by heparin was only 4 mg./100 ml. (S.E., ± 1.24), but this difference was statistically significant. When the heparin was prepared by drying a solution of heparin in 0.9% NaCl a greater difference between serum and plasma was observed. The cholesterol difference (serum minus plasma) producd by Na oxalate increases with increasing amounts of anticoagulant. The decrease in plasma cholesterol concentration produced by the anticoagulants can be explained by changes of water distribution between cells and plasma, reflected by changes of hematocrit produced by the anticoagulant.