ISO 20776-2:2021

Overview

ISO 20776-2:2021 specifies how to evaluate the performance of antimicrobial susceptibility test (AST) devices that produce minimum inhibitory concentrations (MICs) by comparison with the reference broth micro‑dilution method. It establishes acceptable performance criteria, test procedures and data‑analysis approaches for MIC-generating devices used in clinical microbiology. The standard is intended primarily as guidance for manufacturers conducting performance evaluation studies and for laboratories validating AST devices against the ISO 20776-1 reference method.

Key topics and technical requirements

• Scope and purpose: Defines requirements for AST devices that determine MICs of bacteria to antimicrobial agents using pure cultures and standardized broth micro‑dilution conditions (e.g., Mueller‑Hinton broth in microdilution trays).
• Reference method: Uses ISO 20776-1 as the broth micro‑dilution reference against which devices are evaluated.
• Test design elements:
  • Strain selection, including use of contemporary isolates
  • Quality control (QC) of both reference method and device (QC strains and ranges)
  • Reproducibility testing of the device under evaluation
  • Inoculum preparation and isolate testing protocols
  • Discrepancy resolution procedures
• Data analysis and acceptance criteria:
  • Quantitative evaluation for MIC devices using essential agreement (EA) and bias metrics
  • For derivative tests with only 1–3 concentrations, assessment by sensitivity and specificity
  • Requirements for reproducibility and QC performance of the test device
• Annexes: Practical guidance on evaluating MIC performance, rationale for bias analysis, and sensitivity/specificity analyses for qualitative tests (Annex A–C).

Applications and practical value

• Guides manufacturers in planning and conducting performance studies for new or modified AST devices (MIC systems, strips, or panels).
• Supports clinical laboratories and reference labs in verifying device performance before clinical use.
• Informs regulatory and conformity assessment activities by providing standardized evaluation methodology and acceptance criteria for MIC-based AST devices.
• Useful in antimicrobial resistance surveillance, method comparison studies, and product development when quantitative MIC data are required.

Who should use this standard

• In vitro diagnostic (IVD) manufacturers of AST devices
• Clinical microbiology laboratories validating MIC methods
• Regulatory and accreditation bodies reviewing AST device performance
• Research groups conducting comparative susceptibility testing

Related standards

• ISO 20776-1: Broth micro‑dilution reference method (required normative reference)
• ISO 20776 series (other parts for susceptibility testing and related guidance)

Keywords: ISO 20776-2:2021, antimicrobial susceptibility test devices, AST devices, broth micro-dilution, MIC, performance evaluation, quality control, reproducibility, essential agreement, bias, sensitivity, specificity.