Clinical and Laboratory Standards Institute EP47—Evaluation of Reagent Carryover Effects on Test Results provides guidance for planning, performing, evaluating, and documenting reagent carryover experiments along with establishing that no significant reagent carryover occurs by a developer during the Establishment Stage of the Test Life Phases Model (see CLSI EP191). End-user laboratories can use CLSI EP47 to investigate if suspect results are caused by reagent carryover. Assessment and mitigation of carryover risk is described. 

CLSI EP47 is intended to promote uniformity in the evaluation of reagent carryover characteristics of medical laboratory measurement procedures across developers of in vitro diagnostic tests, regulatory organizations, and medical laboratories.

CLSI EP47 is for developers of instrument systems and medical laboratory test methods, both commercially manufactured as well as laboratory-developed tests (LDTs) to eliminate or mitigate reagent carryover. This guideline could also be used for the laboratory end user creating new LDTs, adding open-channel reagents not verified by the manufacturer, or investigating suspect results. 

CLSI EP47 provides recommendations for: 

• Risk assessment criteria to evaluate the potential for reagent carryover effects 

• Statistically valid study designs for evaluation of reagent carryover effects 

• Selection of sample(s) and/or reagent(s) combinations to include in reagent carryover studies 

• Data analysis and interpretation 

• Reporting and/or labeling format for a summary of the reagent carryover effect and performance claims 

CLSI EP47 provides recommendations for the evaluation of reagent carryover from one reagent to another and is intended for quantitative test methods. Qualitative binary methods with an internal continual response and internal cutoff are covered by the recommendations in this guideline. However, CLSI EP47 does not cover semiquantitative test methods characterized as multilevel qualitative assays (eg, assays with an equivocal zone). 

This guideline is not intended to provide detailed guidance for: 

• The evaluation of sample carryover 

• The combined effects of reagent carryover from several different reagents into a single reagent container 

• Carryover between different test methods used to measure the same samples 

• Carryover caused by sample interactions with reagents or cross-contamination from preexamination procedures 

• Carryover within multianalyte assays and/or algorithmic test method 

CLSI EP47 is not intended to be used for verification by the end-user laboratory but can be used to troubleshoot suspect results.