Possible disadvantages of POCT extend into the testing process. Some of these disadvantages include:
- Differences in methodology:
- POCT employs different methodologies. Limitations and interferences can vary from test methods employed in the central laboratory. Limitations include test timing and performing specific steps in the proper order. Contamination and improper sample collection are method/instrument specific. For example, POCT glucose interference may include maltose, galactose, and xylose.
- Proper application of specific test methods. Some POCT test methods must be used for only screening as defined by the manufacturer. These methods cannot be used for diagnoses. Reference the package insert for proper use of a specific method/instrument. A POCT device that is used outside of the manufacturer's instructions results in the method becoming highly complex. If confirmatory testing is required by manufacturer's instructions, the specified process must be followed to maintain CLIA compliance and assigned level of complexity.
- A test kit or device should not be used outside of its intended use or the written procedure (eg, HCG testing on serum in a waived testing setting, when the package insert specifies the waived test is for urine testing only).
- Monitoring and appropriate storage of supplies and reagents: The reagent/QC storage facilities may be decentralized and in remote locations. To prevent deterioration, lack of stock rotation, out dating, and possibly erroneous patient results, a detailed inventory system must be an integral part of the POCT program.
- Reliability of results: Variation in personnel, testing conditions and methods, and perceived simplicity of testing methods all contribute to the potential lack of reliability.
- Personnel: Variation in educational and experience levels of staff performing the tests, as well as potential staff turnover, can impact the reliability of results.
- Test result variability: Compared to central laboratory testing, POCT may experience greater test result variability.
- Simplicity of waived testing is deceptive: Incorrect results can be generated when all variables are considered. Staff training and monitoring with appropriate competency assessment will reduce the level of error.
- Test results may not be comparable to central laboratory results: Methodologies employed in POCT differ from those employed in the central laboratory. Comparison of results or standardization across POCT sites or locations may not be possible. This variability may impact patient care.
- Patient outcome: POCT does not guarantee improved patient outcomes. POCT provides test results with a faster turnaround time in most instances. To effectively expedite clinical management, the entire clinical pathway must be optimized. A faster test result can contribute to the improved patient outcome, but does not provide the sole factor for this final analysis
