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Tuesday, April 14, 2020

Why a COVID19 patients is found positive after some days when first test is negative ?

Why a COVID19 patients is found tested positive after some days when first test is negative ?
Novel Corona Virus Infection Testing.
In early instance when corona virus is just infected someone and Virus RNA in blood is very low level but still its there in very small amount when infection is in a very beginning stage, such patients do become positive when tested later on after few days.

Why in first instance the test comes negative, the test make use of RT PCR techniques, (Reverse Transcriptase polymerase Chain Reaction ) which make use of small fragments of viral RNA, and amplify them and make in test sample so that they are detectable by one or other method of detection.

When there is very lower amount or even in beginning the viral RNA may not come in blood sample so that it could not be amplified in polymerase chair reaction technique.

Therefor a negative test in first instance is always confirmed after few days to check if the viral infection has escaped in first testing.

There are two techniques to identify ncov19 infection.
1) Antibody test : This may come positive even after one is cured from covid19.
2) RT PCR : Test may come out negative in even the virus has just contracted and is in beginning stage. OR person was previously infected and viral load has drooped down, in such instance RT PCR may come negative which must be confirmed after conducting test to check if all viral load is cleared or not.

Polymerase Chain Reaction PCR test
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