Elimination of Error in Hematocrit Produced by Excessive EDTA

Brittin, Geoffrey M., Brecher, George, and Johnson, Carole A.: Elimination of error in hematocrit produced by excessive EDTA. Experience with the Coulter Counter Model S. Techn. Bull. Reg. Med. Techn., 39: 246–249, 1969. We have studied the effects of excessive disodium EDTA on the hematocrit value as determined by the conventional micromethod and by the Coulter Counter Model S, which measures hematocrit indirectly as the product of the red cell count and the mean cell volume. We have also studied a commercial cell control for the Model S which simulates whole blood but crenates the red cells by suspension in a hypertonic medium. Both whole blood with excess EDTA and the commercial cell control give lower hematocrits by the conventional method than when measured by the Model S Coulter Counter. The Model S gives the correct hematocrit value because the 1:50,000 dilution of blood in isotonic medium restores the shrunken red cells to their initial size. It is of practical interest that excess EDTA, which shrinks red cells in proportion to the excessive concentration of anticoagulant and thereby gives erroneously low hematocrit values when determined by the conventional micromethod, does not produce an error in the hematocrit value when it is determined by the Coulter Counter Model S.