Laboratory proficiency testing (PT) is a quality assurance process through which laboratories can demonstrate that they are performing tests competently and producing reliable results. PT involves having a laboratory analyze unknown test samples that are sent to them from an external organization. The laboratory is unaware of the samples' actual values, concentrations, or identities. After analyzing the samples, the laboratory reports its results back to the proficiency testing provider. The reported results are then statistically evaluated against an acceptable range of values to determine if the laboratory performed the testing correctly.
Importance of Laboratory Proficiency Testing
There are several important reasons why PT is essential for laboratories. It allows laboratories to continuously monitor the performance and competence of analysts over time. Proficiency testing can identify problems such as inaccuracies in instrumentation, errors in calibration or sample preparation techniques, misunderstanding of test methods, or improper documentation of results. By addressing any issues caught by Laboratory Proficiency Testing, laboratories can work to improve the overall quality of their testing processes. Proficiency testing also provides objective data to accrediting bodies, regulatory agencies, and clients that a laboratory is producing reliable results. Participation in PT programs is often required for laboratories to maintain their accreditations and certifications.
Types of Laboratory Proficiency Testing Samples
There are different types of samples that may be used in proficiency testing programs depending on the type of testing and analytes involved. Common sample types include:
- Naturally occurring samples - These are clinical, environmental, or food samples that contain the native analytes of interest. They best represent routine client samples.
- Spiked samples - Native matrix samples have known quantities of analytes added to produce samples with values across the reportable range.
- Manufactured samples - These are artificially formulated samples that simulate native matrices. They are cost-effective for producing a large number of homogeneous samples.
- Modified patient samples - Leftover de-identified patient samples may be pooled and have specific analytes adjusted up or down to assigned values.
- Solution samples - Defined solutions have precisely measured analytes prepared in diluted solutions, useful for testing single or multiple parameters.
Frequency of Laboratory Proficiency Testing
The frequency at which laboratories must participate in PT programs depends on their accreditation requirements and types of testing performed. However, most accrediting bodies require biannual or semi-annual testing to ensure laboratories are adequately assessed for ongoing quality control. Some general guidelines on PT frequency include:
- Clinical laboratories - Must enroll in at least two challenge programs per year covering all routine testing areas.
- Molecular/genetics testing - PT may be required quarterly or semi-annually depending on specific assays.
- Water testing laboratories - Typically participate in four to six studies per year depending on drinking water regulations and certification requirements.
- Specialized chemistry and industrial testing - May have annual or biannual participation in specific PT programs depending on scope of accreditation.
Implementation of Laboratory Proficiency Testing Programs
Successful participation in proficiency testing requires both analytical and administrative efforts by clinical laboratories. The key steps laboratories need to follow include:
1. Enrolling in appropriate external PT programs that cover their testing scope and specialties.
2. Proper receipt, identification, and handling of PT samples upon arrival per program instructions.
3. Analyzing PT samples using the same methods, equipment, and SOPs as routinely applied to patient samples.
4. Documenting and reporting results by the specified deadlines without contacting the PT provider.
5. Reviewing final reports to check for any unacceptable performance and investigating potential causes.
6. Taking appropriate corrective actions as needed if performance was unsatisfactory or trends occur over time.
7. Maintaining PT records and performance data as part of the quality system and accreditation documentation.
Effectiveness of Laboratory Proficiency Testing
When implemented properly with corrective actions taken as required, proficiency testing has proven highly effective at improving the overall quality of laboratory testing processes. Studies have shown that participation leads to fewer testing errors, elimination of systematic biases, enhanced competence for personnel, and the potential for cost savings related to fewerrejected patients tests orliability claims. Most importantly, proficiency testing helps assure patients and providers that the diagnostic and monitoring test results produced by accredited laboratories can be trusted for medical decision making and treatment plans.
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