Factor assay (VIII and IX) results in the College of American Pathologists Survey Program (1976-1979). 
Data from the 1976-1979 CAP Surveys for Factor VIII assays are reviewed.  Beginning in 1979, Factor IX assays were also performed by survey participants.  Data was obtained from approximately 2500 laboratories and the different instrument-reagents are ranked according to precision and sensitivity.  Also, the results of questionnaires on specific assay techniques (1977 through 1979) are analyzed.  A trend was noted indicating an increasing number of laboratories are now performing factor assays.  There is poor correlation between precision and sensitivity of most systems (i.e., instrument and reagent combination).  For any given system, there was considerable variation in precision from a normal Factor VIII levels specimen to a low Factor VIII specimen.  This was also the case with respect to Factor IX assays.  With respect to the technical aspects of factor assays there was marked interlaboratory variation (i.e., dilution of normal plasma used to construct standard curve, etc.).  The need for standardization of factor assays is evident from the survey data.