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How External Quality Assessment in the Clinical Laboratory Protects Patient Safety

rows of test tubes

This brief commentary is based upon a talk given at MEDLAB 2018 in Dubai, UAE, which I was honoured to attend as president of the College of American Pathologists. As the title indicates, although an experienced laboratorian can often sense when something isn’t quite right, quality improvement is more about diligence and intentional excellence than intuition. In a few days at MEDLAB and over the course of visits to CAP-accredited laboratories nearby, (including a day-long educational event at the American Hospital Dubai and a workshop sponsored by National Reference Laboratory), I saw that friendliness, diligence, and intentional excellence were in good supply in this new-to-me segment of the global community of pathologists and laboratorians. I am confident that the pace of progress in laboratory quality improvement will only continue to accelerate as international collaboration further diversifies the contributing experiences that drive innovation. 
And now, to our topic… 

A complex, evolving context

Reports from the clinical laboratory have always provided high-impact data points for diagnostic and therapeutic decision making. In recent years, the rapid emergence of targeted therapies has created accelerated demand for companion diagnostics. Clinical laboratories are becoming more visibly integrated in the healthcare system (department-to-department internally and facility-to-facility across the globe) than ever before. All of this makes the old-school notion that the laboratory is an island unto itself more archaic by the minute. It is becoming clearer to more people that excellence in laboratory testing is foundational to patient safety and healing. 

Within the healthcare facilities, a higher profile for clinical pathology has boosted awareness of the human cost when sensitive specimens are improperly managed, especially in the preanalytical phase. Laboratory professionals are educating their partners in specimen collection and transport about the ways that temperature, time, and packaging quality can impact the utility of biological specimens provided to us for analysis. More people are beginning to understand that human materials that are not carefully protected and promptly delivered to the laboratory can quickly degrade. The information that we can elicit from the specimens they collect and transport can define a patient’s future, as our patients are their patients, too. Laboratory quality is everyone’s job.
External quality assessment has one overriding goal: to enhance the quality of care. As the value and promise of laboratory medicine becomes better understood across domains, collaborative efforts to make healthcare quality more uniform and accessible across the globe are growing in tandem. In that context, external quality assessment is getting more attention, as are ways to standardise and harmonise clinical laboratory test results for analytes without available reference measures.

The Mechanics

External quality assessment programmes involve arms-length agreements with providers that validate the accuracy and precision of laboratory test results. The goal is to ensure consistent excellence in clinical laboratory testing so that results are equivalent across sites. 

Proficiency testing is the best-known tool of external quality assurance. Subscribing laboratories receive blinded analytes (sometimes called challenges). The specimens are batched with routine tests and treated exactly like actual patient samples, except that results are sent to the testing programme rather than an ordering physician. The testing programme compares findings to those of peer laboratories to assess consistency and congruity. Failure is defined by a specific significant variance from the mean value for each test within the peer group. 

When a proficiency testing analyte is found to have a concentration or activity equivalent to that of a native (“real”) clinical specimen, that analyte is said to be commutable. Due to the high demand and need for accessibility, proficiency testing analytes are manufactured in large quantities with the most economical materials that will yield results within a clinically relevant range. They are not commutable.

If the macro goal is to make every patient’s test results useful wherever and whenever they seek treatment, then the micro goal may be to help laboratory colleagues appreciate how all the pieces fit together and how they fit in. To that end, much of my discussion at MEDLAB focused on potential new uses for (or approaches to) external quality assessment, viewed through the lens of accuracy-based proficiency testing, a laboratory quality solution developed by the College of American Pathologists.

Accuracy-based Testing: Enter Commutability

The first accuracy-based proficiency testing materials were developed to address inaccurate creatinine results that were causing misclassification of the estimated glomerular filtration rate (eGFR) in patients being screened for chronic kidney disease. The College of American Pathologists introduced this challenge in its proficiency test menu in 2004, naming it the Accuracy-based Creatinine Calibration Verification/Linearity (LN24) Survey.

Accuracy-based challenges are matrix neutral – they contain no stabilisers or antimicrobials, and have limited stability as a result. Their manufacture requires donor/disease-based material, which is in short supply. Target values for accuracy-based challenges are set by high-level reference methods and participant results are graded against the targets rather than peer groups. The 700 surveys offered through the College of American Pathologists programme include seven accuracy-based challenges. Accuracy-based challenges are provided by other external assessment programmes as well.
Because accuracy-based materials contain no additives to prevent breakdown or microbial growth, they must be continually frozen to ensure stability. Laboratories ordering short-stability products need to work closely with their proficiency testing providers to ensure that specimen integrity is continually protected. Distance to the destination as well as time for customs inspections and other importation requirements must be taken into account. 

Commutability is the gold standard. In a perfect world, physicians treating a patient from the United Kingdom who became ill while travelling in China, the United Arab Emirates, or the United States, could comfortably rely upon laboratory test results recorded in his or her home medical record. That’s the big picture. Not the picture as it stands now, but one coming into focus through the collaborative work of laboratory professionals across the globe. Several organisations (eg, the Clinical Laboratory Standards Institute, International Standards Organization, and European Union) are pursuing commutable reference materials for proficiency testing programmes and other quality control purposes.

Definitions from the Clinical Laboratory Lexicon

  • Test results from different methods and manufacturers that agree (within clinically acceptable limits) are said to be harmonised.
  • When a proficiency testing analyte is found to have a concentration or activity equivalent to that of a native (“real”) clinical specimen, that analyte is said to be commutable. This means that test results between field methods and reference methods can be compared directly.
  • Routine proficiency testing materials are artificially produced and not commutable.
  • When two clinically equivalent and properly prepared analytes yield different results, the cause is most likely to be calibration bias (what is true), random bias (what is imprecise), or matrix effects in the sample. While any laboratory test is vulnerable to error or bias, only artificially produced proficiency testing materials have matrix effects.
  • Matrix effects are common, widespread artifacts of material processing (ie, stabilisers and other add-ins to protect against the effects of temperature shifts during shipping). The magnitude of a matrix effect is unpredictable and will vary by method and instrument. At present, only accuracy-based challenges are without matrix effects.
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