Al Hayat International Hospital has introduced a low cost test to detect antibodies against Corona virus called ‘The Antibody Test’.
According to a statement issued by the hospital, there are two types of tests for detecting COVID-19. One test is the Antigen test or PCR test and the other is called the Antibody Test.PCR exists ever since the pandemic arrived in Oman. But the Antibody Test has become available only now, after FDA approval.
PCR test is a swab test which detects virus protein (antigen) in the throat and nose. Usually this test becomes positive by day 1 or 2 of symptoms and becomes negative by about the 14th day. PCR positivity rarely lasts beyond three weeks after onset of illness.
In response to the virus infection, the body produces proteins called antibodies to fight the virus. The antibody test detects these antibodies in blood. There are 2 types of antibodies Ig M and Ig G. Antibodies appear in blood before the end of first week of symptoms and peak in concentration by the second and third week. Ig M antibodies disappear by the end of seven weeks but the Ig G antibody persists. The Ig G antibody is believed to give protection against re-infection (immunity). The long-term persistence and duration of protection conferred by the Ig G antibodies remains unknown.
The advantage of the Antibody Test is that it very economical and probably atone-third the cost of the PCR test.The disadvantage is that itbecomes positive only from the second week of symptoms whereas PCR test is positive in the first week itself. So if you want a diagnosis in a suspected case in the first week of symptoms, you should go for PCR test. If 14 days have already passed after the symptoms started, you may go for antibody test for the diagnosis of recent infection (not acute infection).
How accurate are these tests?
Just like PCR test is negative during incubation period (time period between the entry of virus in the throat and development of fever or cough), the Antibody Test is negative in the incubation period and in the first five days of symptoms.
PCR test in throat plus nose swab is positive only in 70 out of 100 cases. This is called sensitivity. In 30 out of 100 the test can be falsely negative. False negative result is even higher with the PCR test in the second week, whereas the Antibody Test is positive in 90 out of 100 cases in the second and third week.
Between 7 and 14 days ofsymptoms both the tests may bepositive since the antigen comes down but has not touched zero and the antibody curve is going up but has not reached the peak.
What about false positive results ?
With both the tests false positive result is roughly 5 out of 100.
This means that the specificity of the tests is very high (95%)
When is a Covid patient fit to join duty?
The Centers for Disease Control and Prevention (CDC)indicates that health care workers can return to work, if at least 3 days (72 hours) have passed since recovery, defined as resolution of fever without the use of
fever-reducing medications and improvement in respiratory symptoms (cough, shortness of breath) and at least 10 days have passed since symptoms first appeared.
Now we know that Covid infection can be silent in some people. So you may also go for the Antibody Test any time (antibodies remain in blood for many months) even if you never had symptoms, to know whether you had silent infection in the past. Positive Antibody Test may indicate immunity and so presence of antibodies in blood removes the anxiety and fear of contracting the infection again, but this is yet to proved.