Different commercial systems have different strengths regarding NFB. M22-A3 compares these systems.
Within 90 days of implementation, perform an internal audit to ensure 100% compliance with M22-A3. Address any deviations immediately.
The document outlines the "Nested Design" experiment:
Hold a training session on the new QC requirements. Emphasize the clinical importance—for example, how a false-negative on Shigella selective agar could delay outbreak detection.
The M22-A3 provides tables listing:
For each organism, the standard specifies the ATCC or NCTC strain number, incubation conditions, and minimal expected performance.
Last updated: [Current Year]. Always verify that you have the most recent edition of CLSI M22, as standards are revised approximately every 5–7 years.
The most significant feature of the CLSI M22-A3 document is the expanded list of "exempt" media
, which significantly reduces the workload for microbiology laboratories. By classifying certain commercially prepared media as exempt, the standard removes the requirement for end-users to perform redundant quality control (QC) retesting on media with proven reliability. Clinical & Laboratory Standards Institute | CLSI Key Features of CLSI M22-A3 Expansion of Exempt Media
: Based on extensive surveys by the College of American Pathologists (CAP), this version added 27 additional media types to the exempt list, totaling 51 exempt media. New Failure Rate Cutoff clsi m22a3 pdf
: The acceptable extrapolated failure rate for media to qualify as exempt was increased from 0.3% to 0.5% Defined Responsibilities
: It explicitly outlines the specific quality assurance roles for manufacturers, distributors, and users Simplified QC Protocols
: The standard provides streamlined procedures for maintaining quality control organisms and updated incubation conditions for testing. Fastidious Organism Guidance
: It includes new recommendations for the quality control of media used to grow "fastidious" (difficult to grow) organisms. Clinical & Laboratory Standards Institute | CLSI Why This Matters for Laboratories
The "exempt" status means that if a laboratory receives a lot of media from a commercial manufacturer that has already performed QC (evidenced by a Certificate of Quality), the lab only needs to perform physical inspections
(checking for cracks, contamination, or hemolysis) rather than full organism-based performance testing. This saves labs substantial time and money while maintaining high safety standards. ANSI Webstore You can purchase or view more details on the official CLSI M22-A3 product page or access a preview through the ANSI Webstore specific media types are included in the 27 newly exempt categories?
The CLSI M22-A3 standard, "Quality Control for Commercially Prepared Microbiological Culture Media," provides guidelines for ensuring the reliability of ready-to-use media in clinical settings. Published in 2004, the third edition updated QC requirements, including expanding the list of exempt media and defining QC parameters for non-exempt products. The full document can be purchased from the ANSI Webstore ANSI Webstore
CLSI M22-A3, "Quality Control for Commercially Prepared Microbiological Culture Media," establishes protocols for testing ready-to-use media, emphasizing an acceptable failure rate of ≤0.5% for exempt media. While it defines responsibilities for QC, U.S. laboratories have transitioned from these exemptions to Individualized Quality Control Plans (IQCP). Purchase the document through the CLSI Shop.
The CLSI M22-A3 document, titled Quality Control for Commercially Prepared Microbiological Culture Media, is a critical standard used by microbiology laboratories to ensure the reliability of their culture media while optimizing operational efficiency. Published by the Clinical and Laboratory Standards Institute (CLSI), this third edition established the widely used "exempt" media list based on extensive performance data. Understanding the CLSI M22-A3 Standard Within 90 days of implementation, perform an internal
The core premise of M22-A3 is that retesting commercially prepared media is often unnecessary if the media has a proven track record of high reliability. By analyzing failure rates from surveys conducted by the College of American Pathologists (CAP), the CLSI identified specific media types that consistently perform well.
Acceptable Failure Rate: The standard defines an acceptable failure rate as ≤0.5%.
Exempt Media: Media types with failure rates below this threshold are categorized as "exempt" from routine user quality control (QC) testing.
Non-Exempt Media: Media with failure rates >0.5% still require full QC testing by the laboratory for every new lot or shipment. Why Laboratories Need the M22-A3 PDF
Microbiology professionals use the CLSI M22-A3 PDF to determine which media in their inventory require full organism-based testing and which only require a visual inspection.
Regulatory Compliance: While newer CMS Individualized Quality Control Plans (IQCP) have superseded some M22-A3 applications in the US, the standard remains a foundational reference for risk assessment and international lab accreditation.
Cost and Time Efficiency: By identifying exempt media, labs can significantly reduce the amount of time and money spent on maintaining QC organisms and performing redundant tests.
Standardized Procedures: The document provides clear protocols for maintaining QC organisms, incubation conditions, and documenting media receipt. Key Sections of the M22-A3 Standard
The document is structured to guide both manufacturers and laboratory users: The document outlines the "Nested Design" experiment: Hold
Table 2: This is the most referenced part of the PDF, listing various media types and their status as exempt or non-exempt.
Visual Inspection Criteria: Even for exempt media, labs must check for physical defects such as: Cracked Petri dishes or tubes. Excessive bubbles or rough surfaces. Obvious contamination or hemolysis. Incorrect agar depth (less than 3 mm) or unequal filling.
Responsibilities: It clarifies the specific duties of the manufacturer, the distributor, and the end-user laboratory. Where to Obtain the Document
The official CLSI M22-A3 document is available for purchase in PDF or hard copy formats through authorized distributors:
CLSI Official Store: Direct access to the M22 Standard and updates.
ANSI Webstore: Provides the M22-A3 PDF with Digital Rights Management (DRM) protection.
Accuris Standards Store: Offers the M22-A3 (R2018) version, which is the reaffirmed edition of the 2004 standard.
M22-A3 distinguishes between simple linear regression (y = mx + b) and more complex weighted regression (e.g., 1/x or 1/x²). It warns that heteroscedasticity (increasing variance at high concentrations) is common in LC. The guideline provides statistical methods (e.g., lack-of-fit F-test) to verify the calibration model.