Establishing metrological traceability for qualitative test results in a medical laboratory involves ensuring that the reported results are linked to a recognized reference system with a clear chain of comparisons. This ensures the accuracy and reliability of the test results. While qualitative tests are typically based on visual interpretations or binary outcomes, establishing traceability is still important. Here’s how to do it, along with examples:
Steps to Establish Metrological Traceability for Qualitative Test Results:
- Identify the Reference System/Select a Reference Method or Material
Determine the reference system that will serve as the basis for traceability. This could be an established reference method, certified reference materials, or an internationally recognized standard. Choose a recognized reference method, material, or certified reference material (CRM) that is widely accepted and well-characterized for the qualitative parameter being tested
- Chain of Comparisons:
Establish a chain of comparisons that connects your laboratory’s test method to the reference system. This chain includes intermediate steps, if necessary, that link your method to the reference
- Calibration and Standardization:
Implement calibration and standardization procedures to ensure that the instruments and reagents used in your qualitative tests are aligned with the reference system
- Quality Control:
Regularly use quality control materials with known outcomes to monitor the consistency and accuracy of your qualitative test results.
- Participation in External Quality Assessment (EQA) Programs
Enroll in external proficiency testing or EQA programs that provide samples with known qualitative characteristics. Compare your laboratory’s results with the expected results from the EQA program to ensure accuracy.
- Documentation:
Maintain comprehensive records that detail the entire traceability chain, including calibration data, standardization procedures, and quality control results.
Example 1:
Qualitative Blood Type Testing (ABO/Rh Typing):
In blood type testing, the ABO and RhD antigen systems are commonly tested using qualitative methods. Here’s how you could establish metrological traceability for this type of test:
- Reference System:
Choose a recognized reference system, such as the international standard established by the International Society of Blood Transfusion (ISBT)
- Chain of Comparisons:
- Your Laboratory Method (e.g., Slide Agglutination): Link your method to the reference system using a well-documented comparison study.
- Commercially Available Quality Control Material: Use quality control materials with known blood types that are traceable to the ISBT standard
- Calibration and Standardization:
Calibrate and standardize your laboratory instruments according to the manufacturer’s instructions and the reference system’s specifications
- Quality Control:
Run quality control materials with known blood types before testing patient samples to ensure that your test reagents and procedures are functioning correctly.
- Documentation:
Maintain records that document your comparison study, calibration procedures, standardization methods, and quality control results.
Example 2.
Let’s consider two examples of establishing metrological traceability for qualitative test results:
Microbiological Culture Identification
- Reference Method: MALDI-TOF mass spectrometry, a well-accepted method for bacterial and fungal identification.
- Calibration: Validate the laboratory’s bacterial identification method by comparing its results with MALDI-TOF reference results for known culture samples
- Documentation: Document the correlation between the laboratory’s method and MALDI-TOF results for each identified microorganism
By following these steps, you can establish metrological traceability for qualitative blood type testing. While the outcome is binary (e.g., positive or negative for a specific blood type), the process ensures that your results are accurate and comparable across different laboratories and systems.
Example 3.
Pregnancy Test (Qualitative)
- Reference Material: Certified reference material (CRM) containing a known concentration of human chorionic gonadotropin (hCG), the hormone detected in pregnancy tests.
- Calibration: Validate the laboratory’s pregnancy test method using the CRM and compare results with the expected outcome (positive or negative).
- Documentation: Record the CRM used, calibration process, and the laboratory’s method results for the CRM samples.
- In both examples, the key is to establish a clear link between the laboratory’s qualitative test method and a recognized reference method or material. This ensures confidence in the accuracy and reliability of the qualitative test 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 chairmanship in a prominent laboratory organization, 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 resourcesand contact information are available on his websites, https://www.quality-pathshala.com and https://www.sambhuchakraborty.com, or via WhatsApp at +919830051583