Analytical biases with liquid quality control material

Biases were compared for eight analytes determined using common chemistry instruments. Data for three levels of liquid control sera were obtained from over 350 laboratories participating in a quality control program. These data were contrasted with comparable results for lyophilized material and reported in a CAP proficiency survey. In general, biases appeared to be proportional to analyte level. For some analytes, biases with liquid material were less than with lyophilized material, but for most analytes, biases were greater with liquid than lyophilized material. However, when liquid material is used for monitoring interlaboratory precision, the consequences of analytic biases are minimized because of large pool sizes.