Laboratory Proficiency Testing Explained: How PT Programs Ensure Accuracy & Accreditation

Proficiency Testing (PT) is a process designed to evaluate a laboratory’s performance and testing accuracy for specific methods, matrices, and analytes, as compared to other laboratories. Below, we’ll break down how proficiency testing works in a laboratory context and why it’s a vital part of quality assurance and accreditation.

Table of Contents:

• What Is Proficiency Testing?
• How Do Proficiency Testing Programs Work?
• Why Is Proficiency Testing Important?
• Key Takeaways
• More Information
• Questions?

What Is Proficiency Testing?

Proficiency testing is a means of assessing a lab’s performance during the normal sample handling process: receiving, preparation, analysis, quality checks, and reporting. The samples used for this testing are provided by an accredited PT provider. Passing proficiency testing programs is typically required in order for the laboratory to maintain its accreditations.

Proficiency testing samples are to be treated like any other client samples that arrive at the laboratory. By treating PT samples in the same manner as client samples, the laboratory, accrediting bodies, and the laboratory’s clients can obtain:

1. An evaluation of sample handling protocols
2. An assessment of the laboratory’s sample preparation procedures
3. A measure of the accuracy and precision of the analysis
4. An evaluation of the laboratory’s reporting practices
5. Comparative results with those from other laboratories outside the laboratory’s own network

How Do Proficiency Testing Programs Work? 

In a proficiency test, one or more samples are sent to a participating laboratory. Each sample, provided by an accredited PT provider, contains a known concentration of a given analyte, though the concentration is unknown to the laboratory. 

The samples must be prepared and analyzed within a specified time frame and then reported back to the proficiency testing provider. The results are then scored against acceptable limits and compared to those from the group of laboratories that participated in the testing round.

What if a Laboratory Fails a Proficiency Testing Round?

If a laboratory fails a testing round — either by producing results outside the acceptable range or by failing to submit results on time — it must fill out a Corrective Action Request (CAR), a form detailing what went wrong and what will be changed to ensure they do not make the same mistake again.

Proficiency Testing Standards

Requirements vary by Proficiency Testing standard, but one example is under the NELAC Institute’s (TNI) National Environmental Laboratory Accreditation Program (NELAP) standard. Under the NELAP standard, a laboratory must maintain two acceptable PT rounds out of its most recent three attempts for each Field of Proficiency Testing (FoPT). The FoPT is the specific analyte–matrix–method combination.

ISO 17025 and Varying Accreditation Requirements

The broader standard for laboratories, ISO 17025, allows laboratories to determine the frequency of PTs based upon the lab’s individual needs to address both state and national accrediting bodies, which often have different requirements. 

Some accrediting bodies only require one round per year, while others require three rounds per year. Some accrediting bodies require passing scores on all PTs, while others allow two out of three passing scores. 

In some cases, a supplemental PT round may be permitted, allowing the laboratory to order an additional round of testing. This additional round will count as an additional attempt in their PT history.

Why Are Proficiency Testing Rounds Important?

Accrediting bodies rely heavily on the results of PT rounds to determine the competency of a given laboratory. Multiple consecutive failures typically lead to the laboratory being deemed unacceptable for that FoPT until it can demonstrate acceptable PT performance.

Many U.S. states use PT providers accredited by the American Association for Laboratory Accreditation (A2LA) or by the American National Standards Institute (ANSI)’s National Accreditation Board (ANAB). The specific PT provider a laboratory uses will vary depending on the matrices being tested, with different organizations specializing in areas such as soil, food, or water.

Why is Proficiency Testing Important? 

Proficiency testing is important for ensuring consistency in laboratory performance and for maintaining reliability and high standards. It is an important process for any independent, third-party laboratory to undergo regularly. 

According to the International Laboratory Accreditation Cooperation, some of the potential benefits that may be available to laboratories participating in PT programs include:  

• Confirming competent performance
• Identifying testing or measurement issues
• Comparing methods and procedures
• Improving overall performance
• Educating staff
• Instilling confidence in staff, management, and external users of laboratory services
• Comparing operator capabilities
• Generating reference materials
• Determining method precision and accuracy
• Meeting the requirements of regulators and accreditation bodies
• Enhancing risk management

Key Takeaways

• Proficiency testing is a means of assessing a lab’s performance during the normal sample handling process: receiving, preparation, analysis, quality checks, and reporting.
• Passing proficiency testing programs is typically required in order for the laboratory to maintain its accreditations.
• Proficiency testing is important for ensuring consistency in independent, third-party laboratory performance and for maintaining reliability and high standards.

Want More Information about Proficiency Testing?

Below are some additional resources about proficiency testing programs and providers:

NEPTP - The NELAC Institute (TNI)
PT Provider Accreditors - The NELAC Institute (TNI)
Common Proficiency Testing Errors

Questions?

At SimpleLab, we believe environmental data should be a resource for everyone. We’re committed to clarity, efficiency, and trust. Questions? Our customer support team is ready to guide you every step of the way.