Timely case detection is one of the most important steps to prevent and control COVID-19 disease transmission. Since the beginning of the pandemic, laboratories in Indonesia have been using nucleic acid amplification tests (NAATs) such as real-time reverse transcription polymerase chain reaction (rRT-PCR) assay to diagnose COVID-19 cases. However, the gap between the rRT-PCR testing capacity in laboratories and the number of suspected cases to be tested continues to be a major issue.
See more: Covid 19 rdt test procedure
Caption: A rapid chromatographic immunoassay for the qualitative detection of specific antigens to SARS-CoV-2 present in human nasopharynx. Results released within 15-30 mins.
Credit: Baiq Sunarniati – Provincial Health Laboratory Papua Jayapura.
Recently, a new technology has been developed and become available for faster COVID-19 diagnosis. The antigen detection rapid diagnostic test (Ag-RDT) directly detects viral proteins or antigen of SARS-CoV-2, the virus that causes COVID-19, in respiratory samples using a method of lateral flow immunoassay. While this test is less sensitive than the rRT-PCR, it is easy to use and offers faster turnaround time, allowing tests results to become available in less than 30 minutes. It can also be performed directly at point-of-care, therefore no biosafety level 2 (BSL2) laboratory facility is required.
The use of Ag-RDT helps early case detection enormously, which in turn contributes to timely and appropriate patient management and public health decision-making. The exceptional speed of Ag-RDT as well as its other features render the test particularly appealing to be used in locations and high-risk situations with limited resources. Therefore, WHO recommends the use of Ag-RDT to diagnose SARS-CoV-2 infection in settings where NAAT is unavailable or where prolonged turnaround precludes clinical utility.
Confusions and questions often arise regarding the two types of RDT being used in Indonesia, Antigen (Ag) RDT and Antibody (Ab) RDT. The following table illustrates the difference between the two RDTs:
Although there are several Ag-RDT kits available on the market, only few of them have passed WHO’s prequalification process. WHO has been collaborating with the Foundation for Innovative New Diagnostics (FIND) to review Ag-RDT’s performance based on several parameters, such as sensitivity and specificity.
WHO recommends that an Ag-RDT needs to identify more cases than it would miss. This would require an Ag-RDT to have ≥ 80% sensitivity and ≥ 97-100% specificity compared to an NAAT reference assay. So far, only three Ag-RDTs that have met the requirements and have been included in the WHO’s Emergency Use Listing (EUL), but more are expected to be available commercially. With regards to Ab RDT, WHO only recommends this test for research and it should not be used for patient management until more evidence is available to support this purpose.
Based on WHO Interim Guideline: Antigen-detection in the diagnosis of SARS-CoV-2 infection using rapid immunoassays, the followings are some important prerequisites to optimize the performance of Ag-RDT:
- Test should only be performed by trained staff
- Shipping and storage need to be managed
- Shelf-life of test kits as well as specimen quality need to be monitored closely
- Other important considerations during the implementation, including post-market surveillance, which is critical to discover product defects; sample collection method; and biosafety requirements (e.g. PPE use during sample collection).
Indonesia is planning to use Ag-RDT to augment the country’s testing capacity. The use of Ag-RDT could be a game changer in the effort of stopping the chain of COVID-19 transmission in Indonesia. The more cases can be detected at the early stage of the disease, the more interventions can be done by the government to contain the spread of the disease.
For more information about COVID-19 detection and Ag-RDT:
- Diagnostic testing for SARS-CoV-2 – Interim Guidance
- Antigen-detection in the diagnosis of SARS-CoV-2 infection using rapid immunoassay – Interim Guidance
- Advice on the use of point-of-care immunodiagnostic tests for COVID-19 – Scientific Brief