The Sedimentation Rate

The sedimentation rate measures the rate of fall of erythrocytes in the plasma. The rate is accelerated when alterations in plasma protein fractions cause rouleau formation or aggregation of red blood cells due to change in physicochemical properties of plasma and erythrocyte surfaces. These aggregates fall faster than isolated erythrocytes because there is less total surface exposed to surrounding plasma. Methods Textbooks of clinical pathology contain details of the various methods of determining sedimentation rate and the normal values for each method. Disposable tubes are available, and a micromethod is useful for determining the sedimentation rate in infants. The Westergren and Wintrobe methods are most commonly used. Correction for anemia is regarded as inaccurate and is not commonly performed. Since the test is only roughly quantitative, minor variations from the normal values ought to be disregarded. Rates tend to be higher in children, in the elderly, and in adult women.