HSA’s advisory on factors that may affect accuracy of COVID-19 antigen rapid self-test kit results
COVID-19 tests are an important tool in the detection of COVID-19 infection and includes polymerase chain reaction (PCR) tests and antigen rapid tests (ART). While professionally administered PCR tests and ARTs performed by healthcare professionals are expected to have higher accuracy, self-testing remains an essential tool in our public health response during a pandemic as it is readily accessible, cost-effective and gives faster results in the detection of COVID-19.
All COVID-19 ART self-test kits authorised by the Health Sciences Authority (HSA) have been assessed to meet the required safety, performance and quality standards. The test results may however be affected by various factors such as:
- Individual’s viral load
Viral load is the concentration of the virus in a sample. In the early phases of infection, the viral load may be low and may not be detectable. When the viral load is very low, different brands of ART self-test kits may yield different results. There are some differences in the lowest concentration of virus which each of these ART self-test kits can detect due to the different test designs. Therefore, all test results should be considered in the context of an individual’s recent exposures, presence of clinical signs and symptoms consistent with COVID-19.
Therefore, if tested negative but still symptomatic, users should repeat the test after 1-2 days to confirm their infection status as viral loads would have increased to a detectable level by then.
The viral load of an infected individual will also decrease over the course of the infection. In general, tests performed 5 to 7 days after the onset of symptoms or in patients who no longer have any symptoms have comparatively lower viral concentration.
- Sampling method
Inappropriate sampling technique such as not inserting the entire swab tip inside the nose, not swabbing the surfaces of both nostrils, and/or not following the number of sweeping circles on the surfaces of the nostril as recommended by the manufacturer of the test kit may affect the amount of sampling material collected, which may in turn impact the test outcome. To ensure that an accurate test result can be obtained, it is important for users to adhere to the manufacturer’s instructions as directions for use differ across brands.
Companies are required to report to HSA any inaccurate results from their ARTs that they are aware of and investigate them to rule out any quality or performance related issues with their tests. HSA is monitoring the local and global developments closely and will follow up with necessary actions, when required.
Consumers are reminded to only purchase and use tests that have been authorised by HSA.