XXXX activation rate constant: one-stage chromogenic assay for the extrinsic system.

@entity556 @entity3613 @entity797 @entity5630 @entity14420 @entity10281
Some properties of a one-stage, chromogenic clotting assay using tissue thromboplastin as an activator are described. The chromogenic assay uses @entity3613 as substrate and estimates @entity556 by the rate of absorbance produced. Under assay conditions, it was observed that the log ( @entity556 or absorbance/min) is linear with time. The linearity appeared to extend from zero @entity556 up to maximum @entity556 concentration for all concentrations of each plasma type examined including factor V and @entity5630 plasmas. Since the linear slope, b, appears to be a measure of the rate of @entity556 production, it was called the @entity14420 ( @entity14420 ). For dilutions of normal plasma log (b) appears to be linearly related to log (plasma concentration) and to log (PT) where PT is the standard one stage clotting time. For plasmas deficient in extrinsic clotting factors, b was linearly related to log (factor concentrations). The chromogenic assay was most sensitive to changes in prothrombin; least sensitive to changes in factor VII; and unaffected by changes in concentration of factors @entity797 and IX. The standard PT was least sensitive to prothrombin and more sensitive to factors X and VII. For oral anticoagulated plasmas log b and log PT were linearly correlated with a regression slope which was more negative than that from normal plasma. From theses results it was concluded that @entity14420 is a chromogenic assay sensitive to all factors in the extrinsic pathway; that @entity14420 might be used as both a screening assay for @entity10281 and a monitoring assay for anticoagulants; and that @entity14420 may be more sensitive than the standard PT to the defects from oral anticoagulation.
