scope:

This guideline provides recommendations for designing, analyzing, and interpreting linearity studies for quantitative measurement procedures. This guideline is intended for manufacturers and developers seeking to validate the linearity of a measurement procedure throughout a stated concentration interval, especially the interval that includes the measurement procedure's lower limit of quantitation (LLoQ) and upper limit of quantitation (ULoQ). It is also intended for laboratorians who verify the linearity of a measurement procedure and for regulatory agencies responsible for overseeing in vitro diagnostic (IVD) manufacturers or end-user laboratories.

This guideline does not include information on linearity issues encountered during the measurement procedure development phase, such as efficiently identifying the widest possible interval for a linearity claim or selecting calibration points, although the experimental design and data analysis principles described herein can be of value during that phase.

Before the laboratory begins formal linearity verification studies, the measurement procedure's intended analytical measuring interval claim should already have been determined based on the results of linearity, precision, and other studies that have been evaluated using a clinically informed error budget for imprecision, bias, etc.