So far, RT-PCR testing has been the frontline response to the COVID-19. PCR testing is considered as the gold standard for detecting COVID-19 and was designed by WHO, soon after the virus was identified. The PCR test employs reverse transcription of the viral RNA and loop-mediated amplification for the detection of the viral RNA.
The lateral flow immunoassay detects antibodies IgM and IgG and provides historic information about viral exposure of the individual. In comparison, PCR tests are highly accurate but the requirement of shipment of clinical samples takes about 24 hours at best. On the other hand, immunoassays provide results in 20–60 minutes but are less accurate since antibody response takes time to characterize. Several kits with SARS-CoV-2 antigens: the N protein and the S1 and S2 domains of the S protein have been developed with sensitivity over 90%. However, the difference of 10% can initiate the spread of the virus. In early-stage i.e. between 4–10 days, the test provides a sensitivity of just 70% (IgM detection). The sensitivity between 11 and 24 is about 92%. Further, the detection of IgG offers a sensitivity of 98%. Given the circumstances, the integration of PCR testing for a negative result might be useful for battling the COVID-19 outbreak.
Ref: https://www.nature.com/articles/d41587-020-00010-2
https://www.ncbi.nlm.nih.gov/pubmed/32104917
https://www.nature.com/articles/d41587-020-00010-2
https://www.scientificamerican.com/article/heres-how-coronavirus-tests-work-and-who-offers-them/
Always the combination multiple assay are very good.
Immuno assay based on antibody detection and identify the person expose to virus or not.
But identifying the antigen and control the transmission of disease, RT-PCR is the best method.
All the diagnostic method has one or more drawbacks to over come these it is necessary to adopt 1 or more methods.
It not necessary to analyze all the samples in both the methods.
The sample which show positive can take for future analysis.
RT-PCR testing for COVID-19 and testing for SARS-CoV-19 specific antibodies in combination, are the best diagnostic tests.
RT-PCR for SARS-CoV-2 is still the gold-standard test for identifying COVID-19 infection in symptomatic infection or in contacts to decide about isolation of the patient and quarantine of the contacts. However, it's sensitivity depends on the type of sample, expertise of person obtaining the sample and the quality of the kit used. We are seeing patients who despite becoming asymptomatic, becoming negative, one time are becoming positive again.
In patients of COVID-19 confirmed by RT-PCR testing, or their contacts, after 2nd week of symptoms, or asymptomatic period, SARS-COV-2 specific antibody testing can identify:
1. Patients who have recovered, and if admitted to hospital, can be discharged if improved.
2. Patients who can be asked to donate plasma for management of critical COVID-19 cases
3. Patients who are immune to COVID-19 and can go back to work
Combining these 2 tests would increase the sensitivity for diagnosis of COVID-19 infection.
Kiran R and Muhammad Yousuf :
I posted this in another RG question. I think it is an important piece of info. So, I would like to share it here too. Antibody can be detected 10 days after COVID-19 symptoms onset. SARS-CoV-2 virus (antigen) can be detected from symptoms onset and even at day-63 using RT-PCR. So, RT-PCR can detect virus earlier. RT-PCR results are also 'quantitative', which can be used to track a patient's virus load. See the paper below.
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When does the antibody produced after infecting SARS-CoV-2?
I like this study. I have been wanting to know this information.The study tracked the virus and antibody produced in the body of a COVID-19 patient.The paper was published on the Journal of Infection (SCI indexed; Impact Factor for 2018 = 5.09; pretty good journal).
Patient: female, age: 50.
In the figure attached: Panel A-C, tracking the virus in the individual's body from symptom onset to day-63, by testing 3 different protein genes of the virus. Panel D, tracked antibody produced in the individual's body.
The results showed:
1. The virus can be detected in the body from symptom onset to day-63 (using RT-PCR).
2. The individual started to produce antibody at day-10 after symptom onset.
This means: (1) Antibody cannot neutralize virus in a short time. (2) virus can co-exist with our antibody for a while. (3) probably it is more accurate to test virus (the antigen) than test antibody to identify COVID-19, since for a period of time since symptom onset the antibody is not there. (4) the US wants to issue 'antibody pass' to individuals having been infected by the virus, so those people can go back to work. They should also need to make sure that the individual has no virus exist any more.
Paper attached.
Though RT-PCR is the golden standard for detection of COVID19 virus, combination of immunoassay is the best diagnostic tool
Detection of COVID-19 viral antigens and antibody at different time points may work better. Though RT PCR is gold standard, it is time consuming and difficult to serve for huge number of patients and need huge expertise in this field. Immunoassay is very simple and takes less time.
I put it in the following way:
PCR positive Testing confirms-
1. Person has got the viral infection, which is helpful in the initial stages of infection.
2. Person has got the virus, but also confirms antibody test positive too. Means the patient needs to be treated.
3. PCR positive tests also helps finding out the asymptomatic hosts in initial stages ( who can be quarantines)
Antibody test positive means:
1. Symptomatic hosts and antibody test positive.
2. PCR test negative, but antibody test positive means recovered host/ patient. He/ or she can donate plasma to save the lives of other critically ill patients
There´s interesting studies for avian coronaviruses
J. J. De Wit (2000) Detection of infectious bronchitis virus, Avian Pathology, 29:2, 71-93, DOI: 10.1080/03079450094108
The detection methods for infectious bronchitis virus (IBV) are reviewed. Advantages and disadvantages of available techniques of IBV detection by virus isolation, antigen or genome detection, and serology are discussed. Factors of influence on the level of success in detection of IBV after a disease outbreak are discussed, as are the possibilities and dangers of strain classification by protectotyping, serotyping, epitope-typing and genotyping.
Feel free to look through my findings.
https://www.researchgate.net/project/The-Coronavirus-Files
Kiran R
Combination:
RT-PCR tests whether virus (antigen) exist.
immunoassay tests whether antibody exist.
Antigen and antibody can co-exist at some points.
Article On Facing the SARS-CoV-2 (COVID-19) with Combination of Nano...
We generally detect presence of RNA viruses in Plants.It is always good and easy. We generally takes plant leaves samples at Normal temperature or on ice.
Hope, this may helpful to you!
RT-PCR it is.. One cannot be sure of the Accuracy and especially theprecision of immunoassay because Coronaviruses are a broad class of viruses causing a wide range of conditions including a lot which have not even become zoonotic yet and will still be zoonotic in the future. The earlier symptoms are quite alike and the same set of Antibodies as well as class of memory cells are aroused... i recommend it be used as a confirmatory test or a Pre-test especially to eliminate possibility of mixing the uninfected with asymptomatic but for me, RT-PCR is key to this fight. There are other methods which are equally not reliable such as chest Xray.. The presenting xteristics of confirmed patients have thought us more about this novel condition.
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