DISCUSSION
Two main conclusions have been reached in our study. The sensitivity and
specificity levels of rapid antibody tests in detecting COVID-19 cases
confirmed by RT-PCR in the emergency department are 57.5% and 85.5%,
respectively. In addition, thorax CT sensitivity and specificity were
determined as 76.1% and 43.1%, respectively.
Regardless of whether people with COVID-19 infection are symptomatic or
asymptomatic, early and accurate diagnosis is important for treating
patients and reducing the rate of disease spread. Molecular and
serological tests were previously compared during the SARS-CoV-1
epidemic and demonstrated that molecular tests have high sensitivity and
specificity. The current gold standard for SARS-CoV-2 detection is the
SARS-CoV 2-specific quantitative RT-PCR test from a nasal and/or
pharyngeal swab, sputum, or bronchoalveolar lavage (1,9,22–24).
However, if the amount of viral genome in the sample is insufficient or
if the correct window period of viral replication is missed, it may give
false-negative results (25). This situation may result in false-negative
results due to technical problems in sampling, laboratory practice
standards, complex technical procedures and lack of experienced staff.
As a result of a systematic review of COVID-19 test accuracy,
false-negative rates ranging from 2-29% were reported based on the
results of patients whose first RT-PCR result was negative and repeat
tests were positive (26).
Due to the low sensitivity of the PCR test in the diagnosis and
treatment algorithm of the disease, it is aimed to support the diagnosis
and to prevent possible false negativities with thorax CT examination.
In a study performed on 1,014 patients who underwent thorax CT and
RT-PCR tests, the sensitivity of CT was found to be 97% in positive
RT-PCR patients (14). It is thought that CT scanning can help
distinguish COVID-19 positive and negative patients in the emergency
room (27–29). Based on this, guidelines were prepared by the WHO for
the combined use of thorax CT and RT-PCR in the diagnosis of COVID-19
(27).
Due to the lack of diagnostic reagents, some patients can be clinically
diagnosed with thorax CT imaging (21). Some typical radiological images
can be detected by CT in patients with COVID-19 pneumonia. Prominent CT
findings of COVID-19 infection are the appearance of prominent ground
glass density in bilateral, peripheral, and basal regions (30,31). To
date, many descriptive studies and case reports have focused on the CT
findings of COVID-19 (1,32–35). However, clinical and laboratory
findings of COVID-19 infection are indistinguishable from pneumonia
caused by some common respiratory pathogens such as influenza virus,
Streptococcus pneumoniae and Mycoplasma pneumoniae (36).
Chung et al. (34) reported that thorax CT may be negative for viral
pneumonia of COVID-19 at the first admission of patients (3/21
patients). Xi et al. (37) reported 5/167 (3%) patients with negative RT
PCR for COVID-19 at first admission, despite the thorax CT findings
specific to viral pneumonia. In our study, PPV and NPV values of thorax
CT in detecting COVID-19 patients were found at low levels such as
48.2% and 72.1%. This situation was thought to be related to the
normal tomography images of patients who presented especially in the
early period of the disease. Today, with the gradual recognition of the
radiological findings of COVID-19 pneumonia, guidelines are prepared for
prompt and accurate diagnosis (38).
Successful management of disease spread will require serological
detection of past infection to determine immunity (39). Antibodies
specific to SARS-CoV-2 are usually detected within just more than a week
after the onset of symptoms, limiting the role of serology in
identifying acute infection (40). As stated in the literature, it has
been shown that IgM and IgG levels can be measured in patients with
SARS-CoV-2 infection from the first week of the disease or generally
from the second week (41-43). These findings were found to be parallel
to the antibody development characteristics of MERS-CoV infection (44).
This situation restricts the use of antibody tests for screening
purposes during the COVID-19 pandemic (43,45,46).
These limitations have led to the development of different serological
microplate ELISA tests (45,47). Some authors stated that the combination
of molecular and serological techniques can reach a sensitivity of 97%
in the diagnosis of SARS-CoV-2 infection (43,45). However, these
time-consuming tests based on ELISA are generally not as suitable for
clinical use as rapid tests and are difficult to incorporate into
management algorithms in emergency departments (43,45,48,49). Testing
IgM and IgG production in response to viral infection can be a simple
method to increase the sensitivity and accuracy of the molecular test
(45). Additionally, it can be used for screening purposes to evaluate
antibody profiles in a large population. Large-scale screening programs
using the antibody test are currently carried out by different
governments to reveal the percentage of population immunity.
In our study, the sensitivity of the rapid antibody test performed at
the first admission of the patients was evaluated. According to our
preliminary findings, despite the low sensitivity (57.5%), our having
high specificity (85.5%) levels in rapid antibody tests suggests that
the use of rapid antibody test combining with RT-PCR and thorax CT may
prevent false-negative results in our society, which population immunity
is still low.
There are some limitations in our study. First of all, the selection of
patients among the patients who applied to the emergency department made
it difficult to evaluate asymptomatic SARS-CoV-2 carriers. It was
thought that taking the single NS RT-PCR tests taken at the time of
admission as an index caused the false-negative patients to be excluded
due to the low sensitivity of the PCR test. In addition, rapid antibody
tests evaluated in the emergency department was thought to affect the
test results as they could not reach sufficient levels as a result of
not allowing the window time required for antibody development.
In conclusion, rapid antibody test and thorax CT examinations were found
to have low diagnostic value in patients who applied to the emergency
department of our hospital and had a positive first RT-PCR SARS-CoV-2
test. Studies involving larger patient groups are needed for their use
alone in diagnosis and screening.