Precision controls monitor assay random error (reproducibility),accuracy controls assess total error,both random error and systematic error,and trueness (bias)of an assay represents systematic error.A trueness control should be metro-logical traceable,ideally with a target value determined by use of a reference material or a reference method,without metro-logical traceable to a reference measurement system,patient test results for the same patient from different laboratories may not be comparable.A trueness control should be commutable and its analytical response to a reference method and a routine field method should be equivalent to that of a patient sample.And trueness control values should generally be set at medical decision levels and be prepared by the providers of reference materials and manufactured in the same fashion as a calibrator.