The prediction of prothrombin time system performance using secondary standards. 
A method for the comparison of prothrombin time systems using single large lots of lyophilized plasma in the College of American Pathologists Surveys is presented.  Systematic biases for prothrombin time methods as well as for thromboplastins have been measured, and their use allows a very accurate (within 2.25%) prediction of the prothrombin time for the great number of prothrombin time systems presently being used in the United States.