COVID Tests
There is community spread of COVID nowadays. Recently many different tests are carried out about Corona virus in Government and private laboratories. Which test we have to do? Which test takes a lot of time? What is HRCT and it's score? Let me illustrate all.
Mainly there are two kinds of tests for Corona virus 1)Viral test
2) Antibody test
There is no use of Antibody test for diagnosing Corona. Viral test is mainly used for diagnosing Corona.If the infection spreads more in the body then HRCT helps in the diagnosis as well as understanding intensity of pneumonia and function of lungs.
Mainly there are 3 kinds of viral tests namely 1)Rapid antigen test
2)RT-PCR
3)True Nat test
Prices of tests in private laboratories
1)Rapid antigen test- 450 Rs
2)RT-PCR- 2500 Rs
3)True Nat test- 1200 Rs
4)HRCT- 6000-8000 Rs
Time for tests
1)Rapid antigen test- half an hour
2)RT-PCR- 24-48 hours
3)True Nat test- half an hour
4)HRCT- Half an hour to one hour
Which test we have to carry when?
For this Maharashtra Government has given following guidelines -
Antigen test - a)The which needs immediate treatment
RT-PCR- a)For those whose antigen test is negative but still symptoms are there
b) People in the contact of Corona positive patient
c) People coming from foreign countries
True Nat test
a) For brought dead person
b) Delivery woman
c) A patient of emergency operation
(If True Nat test is not available then go for antigen test)
Maharashtra Government has not given the permission for HRCT for diagnosing COVID.It is not valid by the Government for the same.
Let me illustrate all these tests now.
Rapid Antigen Test- 1) In this test antigen protein in the surface spike of virus is checked.
2) For this swab is taken from a nose and a throat.
3) We can get report of this test within half an hour.
4) It is cheaper and instant than RT-PCR test.
5) For this test there is no need of a well trainer.
6) Disadvantages of this test-
a) The sensitivity of this test is 34-80% in case of Corona patients equivalent to Flu disease,so 50% or more than that Covid patients show this test negative.
b) Many asymptomatic patients show this test negative because of unavailability of virus from a nose and a throat as it doesn't involve amplification of antigen.
7) Then why this test is carried out?
a) If viral load is maximum, that time this test is highly sensitive so isolation of patients can be done easily.
b) It is cheaper than RT-PCR and even less time consuming.
c) It's not possible to do RT-PCR for all the patients,so to avoid this tension.
d)To avoid the community spread and quick isolation of positive patients.
e) After doing Antigen test and finding negative but still symptoms are there,then RT-PCR is carried out.
f) Antigen machine is cheaper than True Nat and simultaneously we can carry out many sample checkings through it.
RT-PCR- It stands for Reverse transcriptase-Polymerase Chain Reaction
1)In this test a small fraction of viral RNA can be modified to 1000 times of DNA which are sufficient for the test ( even if we get a small amount of viruses from the swab)
2) Therefore it is considered as the most faithful and correct test for COVID diagnosis.
3) This is however, very tidious test which takes 24-48 hours for the result.
4)For this the swab can be taken from a nose or a throat or even sputum can be taken.
5) For this test there is the need of a well trainer whereas
it is not generally required for other 2 tests.
6) Corona virus Generally grows in a throat in the first week and afterwards in the lungs.That means swab in the throat shows positive test in one week only then afterwards it may show false negative test.Therefore
during the second week of infection, there is the need to check the swab from the nasal tract or sputum with cough.
By watching many videos it is clear that while taking RT-PCR report,we should ask CT (Cyclic Threshold) value.If it is greater than 24 then that person has less viral load and hence transmission through him/her is also less. If CT value is below 24 then that person has more viral load and hence transmission through him/her is also more.
If it is true then still it is observed that having viral load more that person has low or medium symptoms.eg- Small children having seldom intense symptoms can do viral transmission in a big way. Opposite to this when we consider old people having less viral load show intense symptoms.
Actually this is the true contravercy. It is because complications in COVID not only because of virus entered in the body but also of immune system. How does our immune system respond to virus and inflammatory changes? Hence different patients have different kinds of symptoms and evi complications.
CT value specifi tells the actual viral load but not how COVID can be fatal. Therefore ICMR has not permitted to mention CT value along RT-PCR report.
True NAT test-
1) This machine is developed by the company Malbio Diagnostic in Goa.
2) Previously it was used to test TB. Now recently ICMR has permitted it to test COVID19.
3) Having small size it can be taken anywhere through a briefcase.
4)It runs on the battery and once charged can be used upto 10 hours.
5)We can test singly at a time in this machine.If machine has 4 slots then maximum 4 tests can be performed. Maximum we can perform 45 tests among 8 hours of shiept.
6)It can be used in the remote areas where swab can't be transferred to the big laboratory for the RT-PCR test.
7)In this test as like RT-PCR genome of virus is amplified and therefore being low viral load in the swab test comes correctly.
8)In this test specifically E-gene of Corona virus and RdRp enzyme in RNA is searched.
9) It's less time consuming than RT-PCR (only half an hour).Even price for this test is low ( only 1200-1300 Rs). It's very easy to perform and does not require a well trainer or laboratory technician.
10) Machine is costy (price 6.5 lac-12 lac) and it's supply is low hence not available anywhere.
Antibody test
1) The body which is produced against any foreign materials like virus, bacteria,etc called antibody.
2) Antibody test tells information about previous diseases.
3) After infection antibodies are produced within 1-2 weeks hence this test is not useful for COVID diagnosis.
4) Generally all people don't show symptoms during COVID. Therefore it's used to calculate number of COVID patients and their mortality rate.
HRCT
1) It stands for High Resolution Computer Tomography
2) This test is nothing but the CT scan of the chest.
2) Though it's not considered by Government but after getting symptoms if infection increases within 4-5 days,it is carried out to know the intensity of pneumonia and lungs activity.
3)It gives result earlier than RT-PCR and even tells about intensity of pneumonia so it is useful in the treatment of COVID.
4) It's report is faithful and correct one just like RT-PCR.By this test we can understand that whether patient can improve or it's in critical one.
5) After getting symptoms within 4 days,HRCT is not so sensitive hence result may be normal in 50% COVID positive patients but afterwards it's highly sensitive and correct one.
6)In HRCT report following symptoms can be seen-
a)At first (after getting symptoms within 7 days) GGO (Ground Glass Opacity)
b) After 7 days when pneumonia increases
1.GGO increases
2.Crazy paving pattern
3.Consolidation
4.Fibrosis
7) HRCT score
a)HRCT score is given to understand the % of pneumonia in the lungs.
b) It's during 0-25. Zero score means there is no pneumonia in the lungs while 25 score means it is spreaded in the lungs.
c)If score is out of 25
1) Less % of pneumonia- score below 12
2)Medium pneumonia- score among 12-18
d)In order to understand infection in the lungs,HRCT score is generally multiplied by figure 4,but it is not applicable for all the time.
e)In many reports HRCT is given out of 40 then above 2 rules are not applicable.
8) For understanding patient's pneumonia status,we should go for (Reactive protein,Serrum ferritin and Lymphocytes) tests
along with HRCT.
9) X-ray doesn't show starting COVID symptoms like GGO, hence it's not applicable in COVID diagnosis.
COVID Time Line
During COVID what things occur at which day, let us know that
Day zero - Infection of COVID
Day five - Starting of symptoms
Day 1-28 - RNA and Antigen test positive
Day 28 - RNA and Antigen test negative
Day 0-7 - Only RT-PCR test positive
Day 7 - IgM Antibody positive
Day 9 - Symptoms in HRCT
Day 14 - IgG Antibody positive
Day 21 - IgM Antibody negative
Day 14-21 - Symptoms get reduced but transmission to others can be possible
Day 21-28 - RT-PCR may be positive but transmission to others can't be possible
Writer (Microbiologist) - Vishweshwar Kabade
A/P - Andur
Tal - Tuljapur
Dist - Osmanabad
413603
Maharashtra State
Mobile - 9326807480
