Factor XI assay results in the CAP survey (1981).

Data from the 1981 CAP Survey for factor XI assay is reviewed. Different instrument reagent combinations are ranked according to precision and sensitivity. Results of the survey questionnaire are analyzed. There is poor correlation between precision and sensitivity of most systems (i.e., instrument and reagent combinations). For any given system, precision appears to decrease with increasing severity of the factor XI deficiency of the specimen. Some comparisons are made to recent CAP surveys of factor VIII and IX activity. Considerable interlaboratory variation is noted with respect to technical aspects of factor assays (i.e., dilution of normal plasma used to construct the standard curve, etc.). Procedures used by some laboratories in handling patient specimens for factor assays, such as freezing the patient specimen, may decrease the chance of identifying a mild factor XI deficiency. The need for standardization of factor assays is evident from the survey data.