Repeat patient testing quality control (RPT-QC): Background and theory.

Repeat-patient testing quality control (RPT-QC) is a version of statistical quality control (SQC) in which individual patient samples, rather than commercial control materials, are used. Whereas conventional SQC assumes control material stability and repeatedly measures the same lot of control material over time, RPT-QC uses a unique patient sample for each QC event and exploits the labile nature of patient samples under prescribed storage conditions for QC purposes. Advantages of RPT-QC include commutability, lower cost, and QC at concentrations of medical interest. Challenges include sample procurement and the establishment of control limits. The objective of this review is to compare and contrast the principles and procedures of RPT-QC and conventional SQC and to provide an overview of RPT-QC control limit establishment.