DISCUSSION
In recent years, researchers have examined the value of ratios such as
NLR, PLR, and monocyte-lymphocyte ratio (MLR) in the diagnosis and
prognosis of several inflammatory conditions.
The results of this study demonstrated that there was a relationship
between CRP, NLR, and PLR, and the severity score of lung involvement
according to thoracic CT findings in patients with COVID-19 pneumonia.
NLR in the peripheral blood is associated with disease activity and the
systemic inflammatory status, and has been shown to have prognostic
value in autoimmune diseases, malignant tumours, and infectious diseases
(12-15).
In a previous study of 61 COVID-19 patients, NLR was reported to be the
most useful marker showing the incidence of severe COVID-19, with a
cutoff value of ≥3.13 for the differentiation of severe and non-severe
disease(16).
Shang et al evaluated the clinical data of 443 COVID-19 patients and
found that NLR, CRP, and thrombocytes could be useful in determining the
severity of disease, and although NLR was the best determinant, all the
parameters should be taken into consideration (17). PLR, which is a new
inflammation index, reflects the level of systemic inflammation.
Previous studies have reported that PLR is closely associated with
tumours, diabetes, coronary heart disease, and connective tissue
diseases, and an increase in PLR is related to tumour size, lymph node
infiltration, distant metastasis, and prognosis, and could be used as a
potential inflammatory marker for the clinical diagnosis of
community-acquired pneumonia (18).
In a study of 30 patients diagnosed with COVID-19, Qu et al suggested
that an elevated PLR in the blood parameters prolonged the length of
stay in hospital and there could be a relationship with disease
prognosis (19).
The results of the current study demonstrated a weak positive
correlation between the lung involvement severity score determined on CT
and the PLR and NLR in patients who developed COVID-19 pneumonia.
CRP is an acute phase protein synthesised by hepatocytes. In lung
diseases with inflammatory characteristics, the serum CRP level is
generally increased as a response to inflammatory cytokines such as
interleukin-6 (IL-6), IL-1, or tumour necrosis factor alpha (TNF-α) (20,
21).
In COVID-19 patients, CRP increases as a response to pro-inflammatory
cytokines and the majority of previous studies have reported this
increase (22, 23).
In a previous study, CRP levels in COVID-19 patients on hospital
admission were a determining factor independently of disease severity
during hospitalisation, and CRP was reported to show good performance in
the prediction of negative outcomes in COVID-19 patients (24).
In the current study, a moderate level correlation was observed between
CRP levels on admission to hospital and the lung involvement severity
score.
In daily practice, NLR, PLR, and CRP are lower cost markers than
cytokines because blood count is widely used in the clinic routine.
Therefore, NLR, PLR, and CRP on first admission to hospital can be used
as a useful marker of the extent of radiological involvement. The use of
these ratios in the prediction of the severity of the radiological
involvement can provide both early intervention and reduce the exposure
to ionising radiation required by thoracic CT.
Limitations of this study could be said to be the relatively small
patient population, that it was conducted in a single centre, and the
retrospective design. However, to the best of our knowledge, it is the
first study to have been conducted on this subject.
The results of this study demonstrated that it can be concluded that in
COVID-19 patients with higher NLR, PLR, and CRP values, the lungs will
be more affected radiologically. Nevertheless, there is a need for
further studies on this subject.