Activated Coagulation Time of Whole Blood

The determination of the coagulation time of whole blood, as usually performed, has proven an inadequately sensitive means of detecting hemorrhagic diatheses. Many patients with low-grade but potentially dangerous hemophilioid disorders show clotting times well within the normal range. This insensitivity results from two well-established characteristics of the coagulation mechanism: (1) Contact activation, the first and clinically least important stage of the process, requires most of the time of coagulation. (2) Unavoidable variations in degree of contact activation in drawing and observing the blood obscure any but the greatest increases in time of the shorter and more important stages of the process. Insensitivity is therefore inherent in the measurement of coagulation time unless one either eliminates the period of contact activation or, at least, drastically and uniformly shortens it. Many workers have used particulate materials with large surface area to effect quick and maximal contact activation of plasma. In 1958