Interference screening in clinical chemistry is conducted by paired-difference testing: samples with and without the interferent are measured, and the measurand concentration difference is determined.
No practical interference testing strategy can identify all interferents. Some interferents (eg, drug metabolites) may not be identified in the interference screening study. Other substances may be falsely classified as interferents (eg, the form of the substance does not represent the naturally occurring form). An interference screening study provides a standardized evaluation that complements studies of actual patient specimens.
Clinical and Laboratory Standards Institute guideline EP07—Interference Testing in Clinical Chemistry is intended to promote uniformity in the evaluation of interference characteristics of medical laboratory measurement procedures. EP07 describes procedures to screen potential interferents, quantify interference effects, and confirm interference in patient samples. This guideline also describes procedures for medical laboratories to verify interference claims and investigate discrepant results caused by unsuspected interferents. Detailed examples are given. EP07 also contains background information on interference testing concepts. Tables of recommended test concentrations for potential interferents can be found in the supplement, CLSI document EP37.
CLSI also offers a solution package of seven documents that focuses on topics such as interference, linearity, reference intervals, trueness, and precision, including related troubleshooting. Topics covered in this package correspond to CLSI quality system essential Process Management and ISO 15189 sections 5.4 Pre-examination processes and 5.6 Ensuring quality of examination results.