Glossary / Lexicon

Deutsch: Eignungsprüfung / Español: Ensayo de aptitud / Português: Ensaio de proficiência / Français: Essai d'aptitude / Italiano: Prova di competenza

Proficiency testing is a systematic evaluation process used in quality management to assess the competence of laboratories, testing facilities, or individual analysts by comparing their performance against predefined criteria or peer results. It serves as an external validation mechanism to ensure measurement accuracy, consistency, and compliance with international standards, particularly in regulated sectors such as healthcare, environmental monitoring, and manufacturing. By identifying deviations and potential sources of error, proficiency testing supports continuous improvement and maintains confidence in analytical outcomes.

General Description

Proficiency testing (PT) is a structured program in which participating laboratories receive identical samples for analysis under specified conditions. The results are then evaluated by an independent organizer, often an accreditation body or a specialized PT provider, to determine the accuracy, precision, and reliability of the measurements. Unlike internal quality control, which focuses on day-to-day consistency within a single laboratory, PT provides an external benchmark by comparing performance across multiple facilities. This process is critical for demonstrating technical competence, particularly in fields where regulatory compliance or public safety is at stake.

The core principle of PT lies in its ability to detect systematic or random errors that may not be apparent through routine quality checks. For instance, if a laboratory consistently reports values above or below the consensus mean, it may indicate calibration issues, methodological flaws, or operator bias. PT schemes are typically designed to cover a range of analytes, matrices, or measurement techniques, ensuring comprehensive coverage of the laboratory's scope of work. Participation is often mandatory for laboratories seeking or maintaining accreditation under standards such as ISO/IEC 17025, which explicitly requires external performance evaluation as part of its quality management requirements.

PT schemes can be categorized based on their design and purpose. In a "classical" PT scheme, all participants receive identical samples and report their results within a set timeframe. The organizer then calculates statistical parameters such as the assigned value (often the consensus mean or a reference value), standard deviation, and z-scores to assess individual performance. Alternative designs include split-sample testing, where a single sample is divided among participants, or sequential testing, where samples are distributed over time to monitor long-term stability. The choice of scheme depends on the analytical discipline, the complexity of the measurements, and the intended use of the results.

Technical Details

The evaluation of PT results relies on robust statistical methods to ensure objectivity and fairness. The most common metric is the z-score, calculated as:

z = (x - X) / σ

where x is the participant's result, X is the assigned value, and σ is the standard deviation for proficiency assessment. A z-score within ±2 is generally considered satisfactory, while scores outside ±3 indicate a significant deviation requiring corrective action. The assigned value may be derived from a reference material, the consensus mean of participant results, or a value determined by a definitive method, depending on the scheme's design. The standard deviation for proficiency assessment is either predefined by the organizer or calculated from participant data, often using robust statistics to minimize the influence of outliers.

PT schemes must adhere to international standards to ensure their validity and acceptance. ISO/IEC 17043:2010, "Conformity assessment – General requirements for proficiency testing," provides the framework for designing, implementing, and evaluating PT programs. This standard specifies requirements for the competence of PT providers, the selection of test items, the statistical treatment of data, and the reporting of results. Compliance with ISO/IEC 17043 is essential for PT providers seeking accreditation, as it ensures consistency and transparency in the evaluation process. Additionally, sector-specific guidelines, such as those from the European Cooperation for Accreditation (EA) or the International Laboratory Accreditation Cooperation (ILAC), may impose further requirements for particular analytical disciplines.

The frequency of PT participation varies depending on the laboratory's accreditation status, the criticality of the measurements, and regulatory requirements. Some schemes require quarterly participation, while others may be annual or biennial. Laboratories are typically required to document their PT results, investigate any unsatisfactory performance, and implement corrective actions to prevent recurrence. Failure to address persistent deviations may result in the suspension or withdrawal of accreditation, highlighting the importance of PT as a tool for maintaining technical competence.

Historical Development

The concept of proficiency testing emerged in the mid-20th century as laboratories sought to standardize analytical methods and improve the reliability of measurements. Early PT schemes were informal and often limited to specific sectors, such as clinical chemistry or environmental testing, where interlaboratory comparisons were critical for public health and safety. The formalization of PT as a quality management tool gained momentum in the 1980s and 1990s, driven by the increasing globalization of trade and the need for harmonized standards. The publication of ISO/IEC Guide 43 in 1997, later revised as ISO/IEC 17043, marked a significant milestone by establishing international requirements for PT providers and schemes.

The adoption of PT has since expanded across diverse industries, including food safety, pharmaceuticals, and forensic science. Regulatory bodies such as the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA) now mandate PT participation for laboratories involved in drug testing or clinical trials. The rise of digital technologies has further enhanced PT schemes, enabling real-time data submission, automated statistical analysis, and remote auditing. Despite these advancements, challenges remain, particularly in ensuring the homogeneity and stability of test samples, as well as addressing the variability introduced by different analytical methods or equipment.

Application Area

• Clinical Laboratories: Proficiency testing is widely used in medical laboratories to validate the accuracy of diagnostic tests, such as blood glucose measurements, cholesterol levels, or infectious disease screening. Participation in PT schemes is often a requirement for accreditation under standards like ISO 15189, which governs the quality of medical laboratories. For example, the College of American Pathologists (CAP) offers PT programs for over 600 analytes, ensuring that laboratories meet stringent performance criteria.
• Environmental Monitoring: Laboratories involved in testing air, water, or soil samples rely on PT to demonstrate their ability to detect pollutants, heavy metals, or other contaminants. Schemes such as those provided by the U.S. Environmental Protection Agency (EPA) or the European Union Reference Laboratories (EURLs) help ensure compliance with environmental regulations and protect public health. PT is particularly critical for parameters with low detection limits, where small errors can have significant consequences.
• Food Safety and Agriculture: PT plays a vital role in verifying the safety and quality of food products, including the detection of pesticides, mycotoxins, or allergens. Organizations such as the Food and Agriculture Organization (FAO) and the World Health Organization (WHO) promote PT as a tool for harmonizing analytical methods across countries, facilitating international trade. Laboratories accredited under ISO/IEC 17025 must participate in PT schemes to maintain their status and ensure the reliability of their results.
• Industrial and Manufacturing: In sectors such as pharmaceuticals, automotive, or aerospace, PT is used to validate the performance of testing laboratories involved in product certification, material analysis, or process control. For example, the automotive industry relies on PT to ensure the accuracy of emissions testing, while pharmaceutical laboratories use PT to verify the potency and purity of drug products. Participation in PT schemes is often a contractual requirement for suppliers and manufacturers.
• Forensic Science: Forensic laboratories use PT to demonstrate their competence in analyzing evidence such as DNA, drugs, or trace materials. PT schemes in this field are designed to simulate real-world scenarios, ensuring that laboratories can produce reliable results under legal scrutiny. Organizations such as the American Society of Crime Laboratory Directors (ASCLD) and the European Network of Forensic Science Institutes (ENFSI) provide PT programs tailored to forensic applications.

Well Known Examples

• CAP Surveys (College of American Pathologists): One of the largest PT providers for clinical laboratories, offering programs for a wide range of analytes, including chemistry, hematology, and microbiology. CAP surveys are recognized globally and are often required for laboratories seeking accreditation in the United States and other countries.
• EPA Water Pollution Control Program: The U.S. Environmental Protection Agency administers PT schemes for laboratories testing drinking water, wastewater, and environmental samples. Participation is mandatory for laboratories seeking certification under the Safe Drinking Water Act (SDWA) or the Clean Water Act (CWA).
• FAPAS (Food Analysis Performance Assessment Scheme): Operated by the UK-based Food and Environment Research Agency (Fera), FAPAS provides PT programs for food testing laboratories worldwide. It covers a broad spectrum of analytes, including pesticides, veterinary drug residues, and food additives, and is widely used in the food industry to ensure compliance with regulatory limits.
• ILC (Interlaboratory Comparison) Programs by NIST: The National Institute of Standards and Technology (NIST) in the United States offers PT schemes for laboratories involved in metrology, materials testing, and calibration. These programs are designed to support the traceability of measurements to national and international standards, ensuring the accuracy and comparability of results.
• EQA (External Quality Assessment) Schemes by UK NEQAS: The United Kingdom National External Quality Assessment Service (UK NEQAS) provides PT programs for clinical laboratories, focusing on disciplines such as hematology, immunology, and molecular diagnostics. These schemes are essential for maintaining the quality of diagnostic testing in healthcare settings.

Risks and Challenges

• Sample Homogeneity and Stability: Ensuring that all participants receive identical and stable test samples is a significant challenge, particularly for analytes that are sensitive to environmental conditions or have a short shelf life. Inhomogeneity or degradation of samples can lead to inaccurate performance evaluations and undermine the validity of the PT scheme. Organizers must implement rigorous quality control measures, such as replicate testing and stability studies, to mitigate these risks.
• Method Variability: Differences in analytical methods, equipment, or calibration procedures among participants can introduce variability in PT results, making it difficult to establish a meaningful consensus value. For example, laboratories using different techniques for measuring the same analyte may report divergent results, even if their individual measurements are accurate. PT providers must account for method variability in their statistical analysis or specify the use of standardized methods to ensure comparability.
• Data Integrity and Reporting Errors: Errors in data submission, such as incorrect units, transcription mistakes, or misinterpretation of results, can lead to false conclusions about a laboratory's performance. PT organizers must implement robust data validation processes, including automated checks and manual reviews, to detect and correct such errors. Participants are also responsible for ensuring the accuracy of their reported results and documenting any deviations from standard procedures.
• Bias and Collusion: The risk of bias or collusion among participants can compromise the integrity of PT schemes. For example, laboratories may share results or adjust their measurements to align with the expected consensus value, rather than reporting their true findings. To prevent this, PT providers often use blind testing, where participants are unaware of the identity of other laboratories, and implement strict confidentiality protocols. Additionally, statistical outliers are closely scrutinized to detect potential collusion.
• Regulatory and Accreditation Pressures: Laboratories may face significant consequences if they fail to achieve satisfactory results in PT schemes, including the loss of accreditation, reputational damage, or legal liability. This pressure can create a disincentive for participation or lead to "gaming" the system, where laboratories prioritize passing PT over genuine quality improvement. To address this, PT providers emphasize the educational value of PT and encourage laboratories to use the results as a tool for learning and development, rather than a punitive measure.
• Cost and Resource Constraints: Participation in PT schemes can be costly, particularly for small laboratories or those in developing countries. The fees for PT samples, data analysis, and reporting, as well as the time and resources required to prepare for and participate in the schemes, can be prohibitive. Some PT providers offer subsidized programs or reduced fees for laboratories in low-resource settings, but cost remains a barrier to widespread participation. Additionally, the administrative burden of managing PT data and implementing corrective actions can strain laboratory resources.

Similar Terms

• Interlaboratory Comparison (ILC): A broader term that encompasses any comparison of measurement results between two or more laboratories, including proficiency testing. While PT is a specific type of ILC focused on evaluating competence, ILCs can also be used for method validation, standardization, or research purposes. Unlike PT, ILCs may not involve an independent organizer or formal performance evaluation.
• External Quality Assessment (EQA): A term often used interchangeably with proficiency testing, particularly in clinical and healthcare settings. EQA refers to any external evaluation of a laboratory's performance, which may include PT, on-site audits, or peer reviews. While PT is a subset of EQA, EQA programs may also incorporate other assessment methods to provide a more comprehensive evaluation of laboratory competence.
• Round Robin Testing: A type of interlaboratory comparison in which a single sample is circulated among participants for sequential testing. Round robin testing is often used for method validation or standardization but lacks the formal performance evaluation and statistical analysis characteristic of PT schemes. It is typically less structured and may not involve an independent organizer.
• Internal Quality Control (IQC): A process used by laboratories to monitor the precision and accuracy of their measurements on a day-to-day basis. Unlike PT, which provides an external benchmark, IQC focuses on internal consistency and is typically based on the analysis of control samples with known values. While IQC is essential for maintaining quality, it does not replace the need for external validation through PT.

Summary

Proficiency testing is a cornerstone of quality management in laboratories and testing facilities, providing an external benchmark for assessing technical competence and measurement accuracy. By comparing results against predefined criteria or peer performance, PT schemes help identify errors, improve analytical methods, and ensure compliance with international standards such as ISO/IEC 17025 and ISO/IEC 17043. The process is widely used across sectors, including clinical diagnostics, environmental monitoring, food safety, and forensic science, where reliable measurements are critical for public health, regulatory compliance, and consumer protection. Despite its benefits, PT presents challenges, such as ensuring sample homogeneity, addressing method variability, and preventing bias, which require careful management by both PT providers and participants. As laboratories continue to face increasing regulatory and accreditation pressures, proficiency testing will remain an essential tool for maintaining confidence in analytical outcomes and driving continuous improvement.

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