Everywhere(Specifically in villages) a good number of news emerging out about COVID 19 positive cases out of the result of the rapid test. I am a bit confused is it test capable enough to say so.
Sensitivity of rapid cohort RT-PCR versus rapid antibody based SARS-CoV-2 depends on timing of the tests.
Compared with RT-PCR based tests for SARS-CoV-2 (as gold-standard) that have a sensitivity of 70-90%, rapid antibody based test, although quick (results available in 20-30 minutes) have a sensitivity of about 36-69%. Sensitivity of the test will vary according to the timing and sample size of the tests. For example RT-PCR has higher sensitivity in the early phase of symptoms and sensitivity decreases with time decreasing to minimum after 2nd week of COVID-19. Cohort RT-PCR sampling (used for contacts or mass screening at borders) increases sensitivity. Antibody tests will have decresed sensitivity in 2nd week and it increases in sensitivity to maximum in 4th week of COVID-19 illness.
Therefore, rapid antibody based tests for SARS-CoV-2 are not recommended by most of the laboratories for screening because they are more likely to miss many of the positive cases of COVID-19. Again SARS-CoV-2 antibodies will decrease rapidly and may become absent after 3 months or even earlier after 4 weeks, indicating very low seroprevalence of past SARS-CoV-2 infection that is also dependent of age of the patient (5).
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in my experience rapid tests are used for epidemiological surveillance( how many people has been infected with this virus). but some how it might show current.
Muhammad Yousuf Thanks for your response sir. That means, we can not be assured about the presence of COVID 19 by seeing a positive result in the rapid test.
findings come mainly from 38 studies that provided results based on the time since people first noticed symptoms. Antibody tests one week after first symptoms only detected 30% of people who had COVID-19. Accuracy increased in week 2 with 70% detected, and was highest in week 3 (more than 90% detected).
https://www.cochrane.org/CD013652/INFECTN_what-diagnostic-accuracy-antibody-tests-detection-infection-covid-19-virus
Why the antibody-based SARS-CoV-2 rapid tests are not reliable?
Yes, initial diagnosis of COVID-19 is made by RT-PCP of a throat sample (usually nasapharyngeal swab). However, because the rapid tests are dependent on antibody formation, one has to wait 2-3 weeks before the antibody test is positive. Because the antibody formation may be transient in mild cases, they may disappear quickly. This is why antibody based tests may not detect all patients who had been exposed to SARS-CoV-2.
You may like to know about SARS-CoV-2 antibody duration by having a look at this recent article published in NEJM:
Article Rapid Decay of Anti–SARS-CoV-2 Antibodies in Persons with Mi...