Quality control materials in medical laboratories are crucial for ensuring the accuracy and reliability of test results. These materials are carefully manufactured to mimic patient samples, providing a means for laboratories to assess the precision and accuracy of their analytical methods and instruments.
Manufacturing Process: The manufacturing of quality control materials typically involves the creation of a matrix that closely resembles human biological samples. This matrix can be composed of human or animal sera, synthetic compounds, or a combination thereof. Manufacturers add known quantities of analytes (substances measured in an analysis) to this matrix. The mix is then treated to ensure stability and homogeneity, often through processes like lyophilization (freeze-drying).
Characteristics of Quality Control Materials: Quality control materials possess several key features:
- Stability: They must maintain their integrity over time.
- Homogeneity: The contents must be uniformly distributed throughout the material.
- Matrix Match: They should mimic the biological matrix of human samples.
- Known Analyte Levels: The concentration of substances within QC materials should be well-characterized but not necessarily exact, as they are meant to validate performance rather than calibrate instruments.
Purpose of Use: These materials are used to verify the accuracy and precision of laboratory tests. By running QC materials alongside patient samples, labs can detect analytical errors, instrument malfunctions, or procedural issues that could lead to incorrect patient results.
Range Values vs. Fixed Values: Unlike calibrators, which have precise values to set instruments to a known standard, QC materials are assigned range values. These ranges accommodate the inherent variability in biological samples and measurement processes. Ranges ensure that test systems are consistently producing results that are within acceptable limits for clinical decision-making.
Calibrators vs. Control Materials: Calibrator materials are used to set or check the accuracy of measurement scales on analytical instruments. They have an exact known value and are used to calibrate instruments to ensure that the measurements are accurate. On the other hand, quality control materials are not used for calibration; instead, they are used to monitor the precision and accuracy of the testing process after calibration has been completed.
Why Calibrators Are Not Used as QC Materials: Calibrators and QC materials serve different purposes. Calibrators provide a benchmark for the accuracy of an instrument’s measurements. QC materials, with their range values, are designed to simulate the performance of patient samples under routine testing conditions to validate the overall testing process, including the instrument’s calibration.
Nature of Quality Control Materials: Quality control materials are designed to simulate real patient samples. In a biological context, there is inherent variability – no two patient samples are exactly alike. Therefore, QC materials come with an assigned range that reflects this natural biological variability.
Purpose of Range Values: The ranges provided with QC materials are carefully calculated based on statistical analysis of multiple measurements and are intended to reflect the expected variation in test results. When QC materials are tested, the results should fall within this range to indicate that the test system is performing correctly.
Checking Accuracy and Precision: Accuracy in this context doesn’t mean hitting an exact number, but rather consistently producing results within a statistically determined acceptable range. If results from QC materials consistently fall within this range, it suggests that the test system is accurately detecting and measuring the analytes of interest across different runs and over time.
Variability and Day-to-Day Performance: QC materials help monitor day-to-day performance. If results are within the expected range, it implies the system is stable. However, if results drift outside of this range, it may indicate a potential issue with the testing system that needs investigation, even if the exact value of the QC material is not known.
Conclusion:
In essence, QC materials with range values are crucial for ongoing verification of both the precision and accuracy of laboratory tests. They reflect the complexity of biological systems and testing methodologies, guiding laboratories to consistently produce reliable and clinically relevant results.
About the Author
Dr. Sambhu Chakraborty is a distinguished consultant in quality accreditation for laboratories and hospitals. With a leadership portfolio that includes directorial roles in two laboratory organizations and a consulting firm, as well as chairman of IOL ( An ILAC stakeholder organisation), Dr. Chakraborty is a respected voice in the field. For further engagement or inquiries, Dr. Chakraborty can be contacted through email at director@iaqmconsultants.com and info@sambhuchakraborty.com. Additional resources and contact information are available on his websites,https://www.quality-pathshala.com and https://www.sambhuchakraborty.com or via WhatsApp at +919830051583.