Guest blog from: Randox
Laboratory Quality control refers to the process of detecting analytical errors within the lab to ensure both the reliability and accuracy of test results in order to provide the best possible patient care. Unreliable performance can result in misdiagnosis, delayed treatment and increased costs due to retesting etc. it is therefore of great importance to ensure all results provided are both accurate and reliable.
Third party controls is the term used to describe a quality control that has not been designed or optimised for use with any one specific test or system as such they mirror the performance of patient samples and provide an unbiased, independent assessment of analytical performance.
The use of a single multi-analyte third party control will allow you to consolidate your current controls by eliminating the need to purchase individual controls for each laboratory system/instrument. Fewer controls to purchase and stock means fewer controls to manage and fewer vendors to deal with.
As an alternative to third party controls and to reduce costs many laboratories opt to use pooled sera when assessing performance however there are a number of issues associated with using this method.
- Analyte levels will most likely be in the patient normal range and will not be suitable when evaluating performance at clinically significant levels
- The stability would not be validated like a true third party control
- Increased risk of infection as pooled sera may not have been tested at donor level for infectious diseases such as HIV and Hepatitis
- No consistent long term supply, third party controls with an extended shelf life or stability enable long term QC monitoring and allow the detection of shifts upon change of reagent or calibrator lot
Many instrument and reagent manufacturers assign their own control values based on a very limited number of results, this leads to large standard deviations and subsequent unrealistic wide ranges. In fact target ranges are often so wide that the laboratory is unlikely to fall outside them regardless of their performance. In addition to this manufacturers often use the same raw materials in their reagents, quality controls and calibrators as such there is an increased risk that a shift in patient results will go unnoticed as the manufacturers own QC will appear fine.
The Importance of Third Party Controls in Detecting Errors within the Laboratory
The below case studies highlight the importance of third party controls and how they can be used to help detect instrument, reagent and procedural errors.
Detecting Instrument Errors
1. Problem Reported: Customer our Human Assayed Multi-sera on a weekly basis reported a 25% decrease in results for Bilirubin. They ran the reagent manufacturers control on a daily basis and did not see consistently low results.
Resolution: After troubleshooting our control, we sent the customer some of EQA samples. These also recovered approximately 25% low. The customer was able to use this information to refer back to the reagent/instrument manufacturer and later confirmed the low results were due to an instrument fault.
2. Problem Reported: Customer reported their results for Thyroglobulin using our immunoassay control were 4 times higher on their analyser compared to other systems, the instrument manufacturers control however did not show the same problem.
Resolution: We reviewed EQA data for this platform and confirmed there was a big difference in results compared to other instruments. After contacting the manufacturer, they sent us a copy of a customer bulletin advising of a positive bias with certain batches of reagent. The instrument manufacturer did not show the problem the issue may therefore have gone unnoticed if a third party control had not been tested alongside their internal QC.
Detecting Reagent Errors
1. Problem Reported: Customer reported poor recovery for a number of analytes in our immunoassay control. The reagent manufacturers QC however was performing as expected.
Resolution: Investigations showed they had received a notification from the reagent manufacturer regarding changes to the reagent formulation and that the shift seen with our controls was to be expected. The reagent manufacturer’s controls did not show the problem, the issue may therefore have gone unnoticed if a third party control had not been tested alongside their internal QC.
Are Third Party Controls Required for Regulatory Purposes?
Although not required many regulatory bodies and standards from around the world highly recommend the use true third party controls, these include:
The National Association of Testing Authorities, Australia (NATA) recommends the use of independently produced controls over pooled patient sera and manufacturers own controls in Australian Standard 4633 “Supplemental Requirements for accreditation in the field of Medical testing.”
The Clinical and Laboratory Standards Institute (CLSI) encourages the use of third party controls. The Statistical Quality Control for Quantitative Measurement Procedures: Principles and Definitions; Approved Guideline – Third Edition states that “Quality control materials should be different from the calibrator materials to ensure that the QC procedure provides an independent assessment of the measurement procedure’s performance in its entirety, including the procedure for calibration of the measurement.”