Final answer:
EDTA is the preferred anticoagulant in hematologic analysis as it preserves the shape of cells, whereas heparin is also used for plasma preparations.
Step-by-step explanation:
The preferred anticoagulant used to prevent clotting in mammalian blood samples for hematologic analysis is EDTA (ethylenediaminetetraacetic acid). EDTA works by chelating calcium ions necessary for the clotting process, thereby preventing the formation of fibrin clots. In contrast, heparin, another anticoagulant, is often used to obtain plasma rather than for full hematologic analysis as it prevents coagulation by activating antithrombin, which then inhibits thrombin and factor Xa. While blood samples are sometimes collected into tubes containing heparin and can be used in specific hematologic tests, EDTA is generally the preferred choice because it preserves the shape of blood cells and reduces platelet clumping, which is essential when performing complete blood counts and other related tests.