Patient testing is increasingly being carried out at the bedside. Indeed the availability of point-of-care testing (POCT) instruments and devices has grown significantly in recent years. Undoubtedly POCT helps speed up the availability of results, but when such testing is moved outside of the laboratory setting how can accuracy be ensured? `
by Sarah Kee
In all patient testing, Quality Control (QC) exists to ensure accuracy and reliability. For many of the health care workers using POCT instruments, QC will be unfamiliar territory. Many of the standard QC procedures applied in laboratories cannot be applied to POCT devices. However, it is essential that both primary and community care settings apply well-structured QC procedures to ensure the accuracy and reliability of results, minimizing risk to patients and improving patient outcomes.
Designing a QC strategy for POCT
When designing a QC strategy for POCT devices there are three main issues that need to be considered:
1. Design of the devices
POCT devices can be broadly split into three categories with procedures varying according to instrument design:
- “Laboratory Type Instruments”- Full size instruments used at the point of care, e.g.: blood gas analysers.
- “Cartridge-Based Instruments”- E.g.: HbA1c and INR analysers.
- “Strip-Based Instruments”- e.g.: electrochemical or reflectance strip based glucose meters and INR analysers.
For laboratory type instruments the design mirrors that of analysers found within the laboratory environment. Therefore, QC procedures should mirror those found within the laboratory: if patient tests are performed every day, then multi-level QC samples should also be run every day. The accuracy and reliability of these results should be monitored over time to provide a true reflection of performance. External Quality Assessment should be run in conjunction with Internal Quality Control (IQC).
For cartridge-based instruments, the technology differs from that found in standard laboratory type analysers and therefore to reflect this, QC should be performed differently.
Cartridge-based devices usually consist of a cartridge-based component and an electronic reader based component. The cartridge-based component contains all the necessary “ingredients” for the analysis of the patient sample while the electronic reader component is responsible for converting the result from the cartridge component into a numerical value. QC can be problematic as the QC technician is only ever testing the one particular disposable cartridge and the electronic function of the analyser that is in use at that specific time. Nevertheless, performing QC for these devices is still essential to ensuring the cartridge is performing correctly as damage may have occurred during transport, or the on-board reagents may have deteriorated. As a minimum, QC should be run when changing cartridge lot and periodically throughout the lot’s lifespan to ensure the stability of the on-board components. To fully ensure the instrument’s accuracy over time, technicians should also participate in an EQA scheme.
Strip-based instruments are very similar in design to cartridge-based instruments. Like cartridges, the strips are responsible for analysis of the sample, however, as the electronic component has no QC self-check feature, a faulty analyser could be producing erroneous results which remain undetected for some time. Because of this, QC processes should be more stringent for strip-based devices than cartridge-based devices. Strips should be checked on delivery using multi-level QC to ensure they have not been damaged during transit, as well as every day of patient testing. It is also important to participate in a frequent EQA scheme.
2. Possible risks to the patient
When implementing QC for POCT devices the risk of harm to the patient should be the foundation of the QC strategy: where and why do errors occur and what are the consequences of an erroneous result to the patient?
The QC strategy should balance the risk of harm to the patient with the stringency of the QC procedure applied. Studies have shown that the most common phase for errors in POCT is analytical, with 65.3% of errors occurring during this phase. In contrast, the analytical phase in laboratory testing is the least common source for errors. This highlights the need for QC procedures for POCT devices as the potential risk of harm to the patient is greater for POCT than laboratory-based tests.
As many POCT are used by non-laboratory professionals it is vital that users are trained to undertake QC – without QC results may not be accurate. Inaccurate results could have serious implications for the treatment the patient receives.
3. Who is responsible for QC in POCT?
According to ISO 22870:2006, a POCT management group should be set up with responsibility for managing and training staff using the equipment. This group should be responsible for the quality management strategy and implementing a programme of staff training, to include quality control, for all personnel performing POCT and interpreting results.
The running of QC samples on POCT devices should be performed by those who are using the devices regularly, as QC samples should be run as a patient sample would be and therefore must be performed by personnel who are responsible for patient testing.
IQC and EQA/PT – making appropriate choices for POCT Devices
Internal Quality Control (IQC) involves running samples containing analytes of known concentration, to monitor the accuracy and precision of the analytical process over time. Depending on the design of the device and risk of harm to the patient the IQC strategy will differ accordingly. When choosing appropriate IQC material for performing QC on POCT devices, it is important to look for material that offers the following benefits:
- ease of use – many QC materials come in ‘liquid ready-to-use’ formats for convenience
- a matrix similar to the patient sample
- analytes contained at clinically relevant concentrations
- accurately assigned target values
- a third party control, as recommended by ISO15189, to ensure an unbiased, independent assessment of performance
Interlaboratory data management software is available that will allow a laboratory to manage and interpret their QC data. This software is an extremely cost effective and efficient way to ensure that a laboratory’s POCT devices are performing at a high standard, allowing accuracy and precision to be monitored over time, thus providing a true reflection of performance of both the device and the personnel using the device.
This software is usually available with a peer group comparison functionality that will allow a laboratory to directly compare the results of their POCT devices to other laboratories using the same devices worldwide.
Proficiency Testing (external quality assessment) is strongly recommended for all point of care devices. ISO 22870:2006 states, “There shall be participation in external quality assessment schemes”. An EQA scheme assesses the accuracy of the POCT devices through direct results comparison of one device to identical devices worldwide. This peer comparison allows a laboratory to assess the accuracy of a device over time and provides confidence that the patient results being reported are accurate.
There are many PT schemes available for POCT devices; when choosing a scheme it is important that a laboratory considers the following:
- frequent reporting to minimize the amount of time an error can go unnoticed
- quality material provided in a format suitable for use with POCT devices
- well-designed reports that allow for quick and easy troubleshooting of erroneous results at a glance
- choose an international scheme with a large number of participants to ensure a more accurate reflection of performance
The benefits of POCT are undisputed but only if we are assured of accurate results. Getting the right QC strategy in place now will ensure the contribution POCT makes to patient testing is a wholly positive one.
Sarah Kee, BSc PGCE
QC Scientific Consultant
Randox Laboratories Ltd