Of the three ethylenediaminetetraacetic acid (EDTA) salts used for anticoagulation of blood specimens for hematologic testing, potassium salts are the most readily soluble. Tripotassium EDTA is dispensed as a liquid and thus causes a slight dilution of the specimen. This salt also has been shown to affect the red blood cell size more at increased concentrations and on storage than the dipotassium salt. Therefore, dipotassium EDTA is recommended as the anticoagulant of choice in specimen collection for blood cell counting and sizing. The amount of dipotassium EDTA used is 1.5-2.2 mg (3.7-5.4 mumol) per milliliter of blood.