A METHOD FOR CORRECTING THE ERYTHROCYTE SEDIMENTATION RATE FOR VARIATIONS IN THE CELL VOLUME PERCENTAGE OF BLOOD 1

Abstract

Knowledge of the rate of sedimentation of the red blood corpuscles is now generally considered a valuable aid in determining the presence or absence of infection or of tissue damage in the body.2 The test is also of prognostic value and can serve as an index of the relative severity of infection and tissue damage. Obviously the value of the test rests on the assumption that the only factors which affect the rate of settling are directly dependent on the severity of infection or tissue damage. Rourke and Plass (1) have shown that, to obtain a reliable measurement of sedimentation rate, heparin should be used as the anticoagulant, venous stasis should be avoided in collecting the blood, the test should be completed on the day the blood is drawn, and the room temperature during the measurement should remain between 200 and 25°C. These investigators also demonstrated that, all other factors being equal, the rate of settling bears an inverse proportion to the volume percentage of red blood cells; the fewer the red blood cells in a given specimen, the faster the sedimentation rate. If heparinized normal blood is prepared so that the cell volume is only 30 per cent, the sedimentation rate will be as rapid as that of blood from a patient with pronounced infection but with no anemia. The influence of variation in cell volume percentage 1This study was aided by a grant from the DeLamar Mobile Research Fund of Harvard University. 2 Pregnancy is the only physiological process known to be associated with a definite increase in sedimentation rate. 545