Clinical and Laboratory Standards Institute guideline H62–Validation of Assays Performed by Flow Cytometry focuses primarily on analytical method validation. There are currently no official guidance documents for the validation of assays performed by flow cytometry. Existing guidance for the validation of biochemical methods for quantifying soluble analytes found in plasma, serum, and urine is not fully applicable for quantification and characterization of cellular measurands. Validation of flow cytometry is challenging because the data generated are not derived from a calibration curve and true reference standards are lacking. Additional topics covered in this guideline include instrument qualification and standardization and assay optimization. It also covers recommended practices for the examination and postexamination phases. The recommendations presented in H62 are applicable to a wide range of flow cytometry laboratories, including basic research facilities, biopharmaceutical companies, medical laboratories, and manufacturers. This guideline provides specific recommendations for the appropriate analytical method validation approach based on the intended use of the data and regulatory and accreditation requirements, if any, associated with this use. H62 is designed to assist any laboratory using flow cytometry, as well as manufacturers, in developing, validating, verifying, controlling, analyzing, and implementing fluorescence cell-based assays.

This guideline focuses on the unique requirements for the analytical validation of cell-based assays performed by flow cytometry, which are not covered in other CLSI documents. Although flow cytometry can be used for a wide variety of applications other than cellular analysis, this guideline focuses on cellular analysis; however, the general principles are also applicable to noncellular particles. Recommendations and practical instructions are provided for preexamination phase activities such as sample requirements, reagent optimization evaluation, instrument qualification and standardization, and assay optimization and validation. Guidance for examination phase activities such as instrument monitoring and QC are described, as are recommended practices for postexamination activities, including data review, reporting, storage, and retention. This guideline is intended for use in a flow cytometry environment in which preclinical (or nonclinical) and clinical assessments are conducted, including but not limited to: 

• Research laboratories (academic and nonacademic) 

• Medical laboratories 

• Drug discovery, development, and manufacturing companies 

• Reagent, assay, and instrument manufacturers 

• Regulatory agencies 

This guideline provides general recommendations but does not discuss details of specific applications, such as lymphocyte immunophenotyping or neoplastic cell or erythrocyte analysis, which are covered in CLSI documents H42,4 H43,5 and H52.6 The validation of flow cytometric assays for noncellular measurands or soluble analytes is beyond the scope of this guideline. Software validation is also beyond the scope of this guideline. For more information about software validation, see CLSI document AUTO13.7 In a regulated setting, it is highly desirable to use software adhering to 21 CFR Part 11 guidelines8 whenever possible; however, these features are not supported by many flow cytometry software packages. Manual processes must be used to control noncompliant software functionality or to adopt compliant software packages.