In the specialized field of histopathology, the accuracy of testing is crucial for disease diagnosis and research. Compliance with ISO 15189:2022 standards is critical for ensuring quality control within these laboratories. Clause 7.3.7.2 provides a comprehensive approach to Internal Quality Control (IQC), emphasizing the need for histopathology labs to verify the ongoing validity of examination results.
a) Developing and Implementing IQC Procedures:
- Clinical Application: The intended clinical application of histopathological exams must be considered, as performance specifications can vary. For example, the staining intensity and pattern in immunohistochemistry (IHC) are crucial when identifying tumor markers, which may have different performance specifications when used for diagnostic versus prognostic purposes.
- Lot-to-Lot Reagent Variation: Histopathology labs must have procedures to detect variations in reagents and calibrators. For instance, when a new lot of hematoxylin stain is introduced, it’s critical not to change the control slides used for staining quality control on the same day to ensure any differences are due to the new stain batch alone.
- Third-Party IQC Material: Third-party control tissues or slides can provide an objective measure of staining quality in techniques like IHC, ensuring the lab’s staining process consistently produces the expected results.
b) Selecting Appropriate IQC Material:
- Stability: The stability of control tissues or slides, especially those used for enzyme histochemical stains, must be ensured since enzymatic activity can degrade over time.
- Matrix Similarity: IQC materials should have a matrix that closely resembles that of patient samples. For example, control blocks for IHC should contain human tissue to best replicate patient sample reactions.
- Reaction to Examination Method: The control material should react in a manner akin to patient samples. Control slides used for special stains like Periodic acid–Schiff (PAS) should demonstrate a similar level of staining intensity and specificity as patient tissues would.
- Clinically Relevant Challenge: The IQC materials should provide a clinically relevant challenge to the examination method. In histopathology, this might mean having control slides with tissue samples at the threshold of detection for certain pathologies, ensuring the staining process is sensitive enough to detect clinically significant changes.
c) Alternative Methods for Internal Quality Control: When appropriate IQC material is not readily available, histopathology labs are encouraged to employ alternative methods for quality control.
- Trend Analysis: Labs can analyze trends in patient results over time, using statistical methods like moving averages or tracking the proportion of samples with results indicative of specific pathologies. For example, if there is an unexpected upward trend in the incidence of a particular tumor marker, it may signal a need to evaluate the staining process.
- Comparative Analysis: Scheduled comparisons of patient sample results obtained by different validated procedures can serve as a quality check. For instance, results from manual microscopic analysis might be periodically compared with digital image analysis systems, ensuring both methods provide concordant results.
- Retesting Retained Samples: Retaining sections or slides for retesting is a crucial practice. If an issue with a batch of stains or fixatives is suspected, retesting retained samples can validate the integrity of previous diagnoses.
d) Frequency of IQC: The frequency of IQC should be based on the method’s stability and the risk posed by incorrect results. In histopathology, this might mean more frequent checks for rapidly degrading stains or those prone to variability.
e) Data Recording and Analysis: The laboratory must record data in a manner that allows for the detection of trends and shifts. Applying statistical techniques to analyze staining patterns over time can help detect issues before they affect patient results.
f) Review of IQC Data: IQC data should be regularly reviewed against specified criteria. For example, if the intensity of a particular stain consistently falls outside the established range, this could indicate a problem with the staining process that needs to be addressed.
g) Management of IQC Failures:
- Should IQC fail to meet criteria, indicating potential errors that could impact patient care, the lab must reject those results. For instance, if a control slide for an immunostain fails to show the expected reactivity, all patient slides stained with the same batch must be reviewed, and possibly restained, to ensure accuracy.
- The lab must also re-evaluate patient results tested after the last successful IQC but before an identified failure. This ensures any potentially compromised diagnoses are corrected, maintaining the integrity of the patient’s histopathological record.
Adherence to these practices, as mandated by ISO 15189:2022, helps histopathology laboratories maintain high-quality standards in their diagnostic services, ensuring that patient care is based on accurate and reliable test results.
Through adherence to ISO 15189:2022’s IQC requirements, histopathology laboratories can uphold the quality of their diagnostic services, providing clinicians with reliable data for patient care. Regular peer reviews of examination results further enhance the reliability of interpretations, ensuring patient diagnoses are based on sound histopathological evidence.
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