Procedure
for Lab Test of COVID-19
Laboratory testing for SARS-CoV-2 includes methods that detect the presence of virus and those that detect antibodies produced in response to infection.
1. Swab Test: In this test, the lab takes a sample
of cotton swab from inside the throat or nose.
2. Nasal aspirate: The virus examining lab checks
the sample after inserting a solution in the nose.
3. Tresion aspirate: A thin tube called
bronchoscope is inserted into your lungs and samples are taken from there and
examined.
4. Septum test: This is a test of a sample
collected in the lungs or a sample to be extracted from the nose via a swab.
5. Blood test: After collecting all such samples,
it is analyzed according to corona virus and they are blanket tested for all
types of corona virus.
Test Method:
1. RT-PCR: Using real-time reverse transcription polymerase chain
reaction (rRT-PCR) the test can be done on respiratory samples obtained by
various methods, including a nasopharyngeal swab or sputum sample. Results are
generally available within a few hours to 2 days. The RT-PCR test performed
with throat swabs is only reliable in the first week of the disease. Later on
the virus can disappear in the throat while it continues to multiply in the
lungs. For infected people tested in the second week, alternatively sample
material can then be taken from the deep airways by suction catheter or coughed
up material (sputum) can be used.
2. Isothermal amplification assays: On 27 March 2020, the FDA
approved an "automated assay" from Abbott Diagnostics that uses an
isothermal nucleic acid amplification method.
3. Serology: Most serology tests are in the research stage of
development. As of 15 April, three tests had been approved for diagnosis in the
United States, all under FDA Emergency Use Authorization (EUA). The tests are
by Chembio Diagnostic System, Ortho Clinical Diagnostics and Cellex. All three
tests must be performed in a laboratory. The tests by Cellex and Chembio are
rapid diagnostic tests (RTD) that take 10 – 30 minutes to give results. The
test by Ortho is a modified enzyme linked immunosorbent assay (ELISA) that
takes 1 – 5 hours to give results. In China, the Cellex test had a specificity
of 95.6% and a sensitivity of 93.8%. Other tests have been approved in other
countries.
A number of countries are beginning large scale surveys of their
populations using these tests.
Part of the immune response to infection is the production of
antibodies including IgM and IgG. According to the FDA, IgM antibodies to
SARS-CoV-2 are generally detectable in blood several days after initial
infection, although levels over the course of infection are not well
characterized. IgG antibodies to SARS-CoV-2 become detectable later and
normally peak around 28 days after the onset of infection. Antibody tests can
be used to determine the percentage of the population that has contracted the
disease and that is therefore immune.
Assays can be performed in central laboratories (CLT) or by
point-of-care testing (PoCT). The high-throughput automated systems in many
clinical laboratories will be able to perform these assays but their
availability will depend on the rate of production for each system. For CLT a
single specimen of peripheral blood is commonly used, although serial specimens
can be used to follow the immune response. For PoCT a single specimen of blood
is usually obtained by skin puncture. Unlike PCR methods an extraction step is
not needed before assay.
In late March 2020, a number of companies received European
approvals for their test kits. The testing capacity is several hundred samples
within hours. The antibodies are usually detectable 14 days after the onset of
the infection.
In early April, the UK found none of the antibody test kits it
purchased were sufficiently good to use.
4. Medical imaging: Chest CT scans may be helpful to diagnose COVID-19 in
individuals with a high clinical suspicion of infection based on risk factors
and symptoms but is not recommended for routine screening. Typical features on
CT initially include bilateral multilobar ground-glass opacities with a
peripheral, asymmetric and posterior distribution. Subpleural dominance, crazy
paving, and consolidation may develop as the disease evolves.
Considering the Pandemic situation, everyone is advised to stay home and stay safe during lockdown and thereafter observe social distancing and take advised necessary precautionary measures.
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