In the field of microbiology, the reliability of test results is a critical component of patient care. ISO 15189:2022 outlines stringent guidelines for internal quality control (IQC) procedures in medical laboratories to ensure the consistency and accuracy of test results. Here is how a microbiology laboratory might apply these requirements:
a) Establishing IQC Procedures:
- Clinical Application Consideration: The laboratory must ensure that the IQC procedures are relevant to the clinical scenarios in which tests are applied. For example, the performance specifications for a methicillin-resistant Staphylococcus aureus (MRSA) screen may vary between routine surveillance and post-surgical infection investigations.
- Lot-to-Lot Variation Detection: The procedures should facilitate the detection of variations due to changes in reagent or calibrator lots. A microbiology lab, for instance, should not switch control materials for bacterial culture media on the same day they switch to a new reagent lot, to avoid confounding variables.
- Use of Third-Party IQC Material: Third-party control materials for assays like antibiotic susceptibility testing can offer an unbiased verification of the test system’s accuracy, independent of the reagent suppliers’ materials.
b) Selecting Appropriate IQC Materials:
- Stability: The selected control organisms, such as quality control strains for antimicrobial susceptibility testing, must demonstrate stable resistance patterns over time.
- Matrix Similarity: The control materials should have a matrix that closely mimics patient specimens. This can be particularly important in tests like fungal cultures, where the medium’s composition can affect the growth rate and morphology.
- Reaction to Examination Method: IQC materials should react to the examination method similarly to patient samples. For instance, control strains used in PCR assays for pathogen detection should amplify with the same efficiency as clinical samples.
- Clinically Relevant Challenge: The control materials should challenge the lab’s methods at clinically important levels, such as having bacterial loads near the limit of detection for assays like Legionella water testing, ensuring the test can accurately identify clinically significant levels of the pathogen.
c) Alternative Methods for Internal Quality Control: When standard IQC materials are not available, microbiology laboratories must adopt alternative quality control methods.
- Trend Analysis of Patient Results: For example, a laboratory may use a moving average of patient results for MRSA detection rates. If there is a sudden increase in positive results, it could indicate a potential contamination issue or an actual outbreak.
- Comparison with Alternative Procedures: A lab might regularly compare the sensitivity of its in-house bacterial culture methods against a molecular method, like qPCR, that is validated and traceable to higher order standards. This comparison can ensure that culture methods are detecting pathogens at expected rates.
- Retesting of Retained Patient Samples: If an issue is suspected with a batch of media used for tuberculosis cultures, previously retained patient samples may be re-cultured on a new media batch to verify the accuracy of initial test results.
d) Frequency of IQC: The frequency of IQC should reflect the method’s stability and risk to patients. High-risk tests, such as blood cultures for septic patients, might require more frequent quality control than less critical tests.
e) Data Recording and Analysis: Recording data to highlight trends and shifts is crucial. A laboratory might use statistical process control for daily quality control data on antibiotic susceptibility tests, allowing for the early detection of resistance pattern shifts.
f) Review of IQC Data: IQC data must be reviewed against established criteria regularly. For instance, any variation in the control plates for disc diffusion susceptibility testing beyond acceptable limits would trigger a review of testing protocols.
g) Handling IQC Failures:
- When IQC does not meet acceptability criteria, indicating clinically significant errors, all affected results must be rejected. For example, if a quality control strain shows unexpected resistance, all susceptibility tests conducted since the last successful control must be reconsidered.
- Patient results must be re-evaluated if they were tested after the last successful IQC but before an identified IQC failure. This ensures that no incorrect results are reported to clinicians, which could lead to inappropriate treatment decisions.
These IQC procedures are vital for maintaining the high standards required in microbiology labs, which are essential for accurate diagnosis and effective treatment. By following the guidelines of ISO 15189:2022, laboratories can assure healthcare providers and patients of the reliability and validity of their testing services.
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