2020-03-18 15:19:03 14:50       作者:

Which is the best method?

  —Tests for SARS-CoV-2 Infection Diagnosis

For confirmed COVID-19 cases, reported the common clinical symptoms 
include fever,cough,myalgia or fatigue. Yet these symptoms are not unique
features of COVID-19 because these symptoms are similar to that of other
virus-infected disease such as influenza. Currently, virus nucleic acid
Real-Time PCR (rt-PCR),CT imaging and some hematology parameters are
the primary tools for clinical diagnosis of the infection. Many laboratory test
kits have been developed and used in testing patient specimens for COVID-19
by Chinese CDC1, US CDC2 and other private companies. IgG/IgM antibody
test, a serological test method, has also been added as a diagnostic criteria in
China’s updated version of the diagnosis and treatment guidelines for the
novel coronavirus disease (COVID-19), which was issued on 3rd, March1.The
virus nucleic acid rt-PCR test still is the current standard diagnostic method for
diagnosis of COVID-19.



Novel Coronavlrus (SARS-COV-2)

 Multiplex Real-Time PCR Kit(detection for  three genes)

Yet these real-time PCR test kits, looking for genetic material of the virus,
for instance in nasal, oral, or anal swabs, suffer from many limitations:

1) These tests have long turnaround times and are complicated in
operation; they generally take on average over 2 to 3 hours to generate results.

2) The PCR tests require certified laboratories, expensive equipment and
trained technicians to operate. 

3) There are some numbers of false negatives for rt-PCR of COVID-19. It
may due to low SARS-CoV-2 viral load in the upper respiratory swab specimen
( Novel coronavirus mainly infects the lower respiratory tract, such as
pulmonary alveoli ) and the test can’t identify people who went through an
infection, recovered, and cleared the virus from their bodies. 

Research by Lirong Zou et al4 found that higher viral loads were detected
soon after symptom onset, with higher viral loads detected in the nose than in
the throat and the viral nucleic acid shedding pattern of patients infected with
SARS-CoV-2 resembles that of patients with influenza
4 and appears different
from that seen in patients infected with SARS-CoV-2.

Yang Pan et alexamined serial samples (throat swabs, sputum, urine, and
stool)from two patients in Beijing and found that the viral loads in throat swab
and sputum samples peaked at around 5–6 days after symptom onset, sputum
samples generally showed higher viral loads than throat swab samples. No viral
RNA was detected in urine or stool samples from these two patients.

PCR test only give a positive result when the virus is still present. The tests
can’t identify people who went through an infection, recovered, and cleared the
virus from their bodies. In acturely, only about 30%-50% was positive for PCR
in patients with clinically diagnosed novel coronavirus pneumonia. Many novel
coronavirus pneumonia patients can not be diagnosed because of negative
nucleic acid test, so they can not get the corresponding treatment in time. From
the first to the sixth edition of the guidelines, relying solely on the basis of the
diagnosis of nucleic acid test results, which caused great trouble to
The earliest "whistle-blower", Dr. Li Wenliang, an ophthalmologist at
Wuhan Central Hospital, is dead. During his lifetime, he had three nucleic acid
tests in the case of fever and cough, and the last time he got PCR positive results. 

After discussion by experts, it was decided to increase serum testing methods
as a new diagnostic criterion. 
While antibody tests, also called serological tests,
that can confirm whether someone was infected even after their immune
system has cleared the virus that causes COVID-19.




IgG/IgM Antibody Rapid Test



IgG/IgM antibody test will help to trace in a much more population-based way who
has had the infection, because many cases seem to be spread from asymptomatic
patients who can’t be identified easily. A couple in Singapore, the husband tested
positive by PCR,his wife’s PCR test result was negative, but the antibody test results
showed that she had antibodies, as did her husband.
Serological assays need to be carefully validated to be sure they react reliably, but
only to antibodies against the novel virus. One concern was that the similarity
between the viruses that cause severe acute respiratory syndrome and COVID-19
could lead to cross-reactivity. The IgG-IgM developed by Xue Feng wang6 was
considered to be able to be used as a point-of-care test (POCT), as it can be
performed near the bedside with fingerstick blood. The kit has sensitivity of 88.66%
and specificity of 90.63%. However, there were still false positive and false negative
In China’s updated version of the diagnosis and treatment guideline for the
novel coronavirus disease (COVID-19)
1, confirmed cases are defined as
suspected cases who meet any one of the following criteria:

(1)Respiratory tract samples,blood or stool specimens tested positive for
SARS-CoV-2 nucleic acid using rt-PCR;

(2)Genetic sequencing of virus from respiratory tract,blood or stool
specimens samples is highly homologous with the known SARS-CoV-2;

(3)Serum novel coronavirus specific IgM antibody and IgG antibody were positive;

(4)Serum novel coronavirus-specific IgG antibody changed from negative
to positive 
or coronavirus-specific IgG antibody during recovery period is 4
times higher than that during the acute period.

Diagnosis and treatment of COVID-19

Version 7th 3Mar.2020
❸ IgM+IgG
Version 6th
Version 5th
Version 4th
Version 3rd
Version 2nd
Version 1st
18 Feb.2020
3 Feb.2020
27 Jan.2020
22 Jan.2020
16 Jan.2020


1. Guidelines for diagnosis and treatment of novel  coronavirus pneumonia (trial version
7,National Health Commission of the People's Republic of China ,issued at 3 Mar. 2020)
2. Research Use Only Real-Time RT-PCR Protocol for Identification of 2019-nCoV 
3. Singapore claims first use of antibody test to track coronavirus infections 
4. SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients February
19,2020 DOI: 10.1056/NEJMc2001737
5. Viralloads of SARS-CoV-2 in clinical samples Lancet Infect Dis 2020 Published Online
February 24, 2020     
6. Developmentand Clinical Application of A Rapid IgM-IgG Combined Antibody Test
for SARS-CoV-2  Infection Diagnosis XueFeng Wang ORCID iD: 0000-0001-8854-275X






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