Covid 19 : RT PCR test – Frequently asked questions

1. *What is the full form of RT PCR?*

Ans : Reverse Transcription Polymerase Chain Reaction

2. *Why test is only 67% specific & not 100% ? What are the pitfalls?*

Ans : Problem can be at 4 levels :

– very low viral load at the time of sample collection

– faulty sample collection

– improper trans port of the sample &

– faulty laboratory technique.

So test must be repeated in high clinical suspicion.

3. *How the test is correctly interpreted ?*

Ans : Correct interpretation – at least two or more antigens should be tested with same reagents & same laboratory.

4. *Is there any false positive result ?*

Ans : No false positives- positive is certainly positive. It can be false negative. (Repeat the Test- if high clinical suspicion)

5. *How many types of antigen are present in COVID- 19 virus?*

Ans : Covid-19 virus has 6(six) antigens-

– E
– S
– N
– ORF 1a
– ORF 1 b &
– RDRP.

6. *Which antigen is common to all corona viruses?*

Ans : E antigen is common to all CORONAVIRUSES.

If E is negative – No Corona.

Other 5 are specific to Covid-19.

7. *Do all countries test same antigens?*

Ans : Testing of antigen differ from one country to another.

8. *What is is the implication of it on international travellers?*

Ans : As testing of antigen differ from country to country. So person declared negative in one country may test positive elsewhere. It depends on antigen/s being tested.

9. *Is positive/ Negative report enough?*

Ans : No, simply mentioning positive/ negative in certificate has no meaning.

10. *How can a Doctor certify that patient is non- infectious?*

Ans : Along with positive/negative report, Doctor must be able to certify that person is infectious/non- infectious under following conditions.

a) Patient demonstrates presence of IgG antibodies with or without presence of antigen.

b) Patient is asymptomatic after 10 days without doing antigen test.

c) Patient is positive for two weeks and his/ her ESR , CRP are normal ??

11. *After how many days in body virus becomes non replicable/ non culturable?*

Ans : After 10 days virus is nonreplicable. So test is not required after 10 days.

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