Discussion
Our study revealed that WBC, LYM% and PLT decreased, while CRP and Hb
increased significantly in nucleic acid positive group compared to those
in nucleic acid negative pneumonia group. LYM%, Hb and WBC had a good
predictive value to distinguish the nucleic acid positive patients from
negative patients. The dynamics of WBC, LYM%, Hb and CRP in nucleic
acid positive patients were more sensitive to clinical treatment and
gradually returned to normal level. Only LYM% had a significant
correlation with C t value.
COVID-19 caused by SARS-CoV-2 with high
transmissibility[10] is an ongoing
global pandemic[11]. Given the global
spread of COVID-19, strict discharge standard is of great significance
for the prevention and control of the epidemic.
At present, the criteria for discharge is 1) temperature returns to
normal for more than three days, 2) respiratory symptoms improve
significantly, 3) pulmonary imaging shows significant improvement in
acute exudative lesions, and 4) nucleic acid test is negative for two
consecutive times for samples of sputum, nasopharyngeal swabs, and other
respiratory tract specimens, tested at intervals of at least 24 h.
Therefore, negative nucleic acid test is indispensible for patients’
discharge[12]. However, there are no
available parameters to accurately determine when patients will test
negative for SARS-CoV-2 during clinical treatment.
The nucleic acid testing time is based on the clinical improvement of
patients which is partially subjective and lacks objective indicators.
The clinical and radiographic manifestations of many patients improved
significantly with time, but the actual viral load was still high.
Therefore, patients often need to take nucleic acid test again and again
which brings discomfort to patients during the sampling process,
increases the infection risk of medical staff and consumes limited
medical resources, resulting in their
wastage[13].
Lymphocytes% commonly decreases in the early stage of
disease[14,
15] and could be an indicator of
reflecting COVID-19 severity and
prognosis[16,
17]. LYM% can be used as a reliable
indicator to classify the moderate, severe, and critical ill patients
independent of any other auxiliary
indicators[18]. The COVID-19 is much
more serious with lower Lymphocytes
[19]. SARS-CoV-2 RNA load is also
closely related to COVID-19 severity
[20]. The relative RNA load is
higher, the lymphocyte count was
lower[21].
LYM% can be easily acquired from Blood routine test which requires low
cost and the whole process is easier and convenient
[22]. There is no standard guideline
to accurately determine the timing of SARS-CoV-2 nucleic acid detection
until now. Our study confirmed that: 1) LYM% of COVID-19 pneumonia
patients was decreased compared to those of common pneumonia patients,
2) LYM% had a good predictive ability to distinguish the nucleic acid
positive from negative pneumonia, 3) LYM% dynamics of COVID-19 were
sensitive to clinical treatment and 4) LYM% had a significant
correlation with C t value(reverse to viral RNA
load). So, we suggested dynamically observing the changes of LYM% may
be used to estimate the time for SARS-CoV-2 nucleic acid test results
turning negative in COVID-19 Patients.
However, more laboratory test results need to be comprehensively
analyzed to explore a quantifiable standard of LYM% to accurately guide
the timing of SARS-CoV-2 nucleic acid turning negative detection during
the treatment course of COVID-19.
This study has three limitations. First, this is a retrospective study.
The cases were only from the Xiangyang central hospital. Second, only a
few relevant studies are available, and this study only analyzed the
correlation between LYM% and C t value, but the
quantifiable LYM% is not clear. Third, for greater convenience in
statistical analysis, we used a range of lymphocyte count that did not
account for the effects of age and gender on the lymphocyte count.