In clinical pathology, particularly in the analysis of urine and stool samples, maintaining the validity of test results is crucial for accurate diagnosis and patient management. ISO 15189:2022 outlines comprehensive internal quality control (IQC) procedures that are essential for ensuring consistent and reliable test outcomes in these areas.
a) Establishment of IQC Procedures:
- Clinical Application Consideration: The laboratory must ensure that IQC procedures are appropriate for the intended clinical use of the tests. For example, the sensitivity required for detecting glucose in urine for diabetes screening might differ from that needed for more nuanced assessments in renal disease management.
- Lot-to-Lot Variation Detection: It’s vital for laboratories to have procedures that detect variations due to changes in reagents or calibrators. For instance, when introducing a new lot of reagents for stool occult blood testing, changing the control material on the same day should be avoided to ensure that any observed variation is due solely to the new reagent lot.
- Use of Third-Party IQC Material: Third-party control materials for tests like urine specific gravity or pH can offer an independent check against the manufacturer’s control materials, providing an unbiased assessment of the test system’s performance.
b) Selection of Appropriate IQC Materials:
- Stability: Control materials, such as those used in urinalysis, must demonstrate stability. For instance, synthetic urine controls used for chemical analysis should retain their chemical properties over their shelf life.
- Matrix Similarity: The control materials should mimic the matrix of patient samples as closely as possible. In stool testing, for instance, the control material should have a similar consistency and composition to actual stool samples to ensure accurate results.
- Reaction to Examination Method: IQC materials should react to the examination method in a similar way to patient samples. In urine sediment analysis, the control material should produce findings comparable to those expected in patient urine under the microscope.
- Clinically Relevant Challenge: The control material should challenge the examination method at clinically significant levels. For example, in a fecal immunochemical test, control materials should have hemoglobin levels at or near the clinical decision limit to ensure the test’s sensitivity and specificity.
c) Alternative Methods for Internal Quality Control: In scenarios where standard IQC materials are unavailable, clinical pathology labs must utilize other methods to ensure quality control.
- Trend Analysis of Patient Results: Laboratories can employ trend analysis, such as moving averages, to monitor patient results over time. For instance, tracking the frequency of abnormal results in urine protein tests can help identify potential issues with test procedures or reagents.
- Comparison with Alternative Procedures: Regularly comparing results from patient samples with those obtained using an alternative validated procedure can provide additional assurance of accuracy. For example, comparing microscopic findings of stool samples with results obtained from an immunoassay for parasitic infections ensures consistency between different testing methods.
- Retesting Retained Samples: If there’s suspicion of an error or inconsistency, retesting retained patient samples can validate the accuracy of recent test results. This practice is particularly crucial in urine analysis, where factors like sample stability can impact the test outcome.
d) Frequency of IQC: The frequency of IQC should align with the stability and reliability of the test method, as well as the risk to patient care from incorrect results. High-variability tests, like stool occult blood tests, may require more frequent quality control than more stable tests.
e) Data Recording and Analysis: Accurate recording of IQC data is essential for detecting trends and shifts. Statistical methods can be employed to analyze this data, such as control charts for monitoring the consistency of urine pH measurements.
f) Review of IQC Data: Regular review of IQC data against predefined acceptability criteria is necessary. Any deviations should prompt immediate investigation to identify and correct the cause.
g) Management of IQC Failures:
- If IQC fails to meet the acceptability criteria, indicating potential clinically significant errors, those results must be rejected. For example, if a control sample in a urine electrolyte test shows unexpected results, all patient samples tested since the last successful control would need to be reviewed and possibly retested.
- The results of patient samples tested after the last successful but before a failed IQC event should also be re-evaluated to ensure their accuracy and reliability.
By adhering to ISO 15189:2022 standards, clinical pathology laboratories specializing in urine and stool analysis can ensure the ongoing validity and reliability of their examination results. This leads to high-quality patient care and accurate clinical decision-making based on dependable laboratory data.
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