Role of Inflammatory Markers and Computed Tomography Severity Score in Predicting the Severity and Clinical Outcome in Patients with COVID-19

Introduction

Coronavirus disease 2019 (COVID-19 disease) caused by Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, first appeared in Wuhan city of China in December 2019, which subsequently spread all over the globe. Many people were affected in different ways. Patients with certain underlying co-morbidities were at a higher risk of progressing to severe disease. Several inflammatory markers such as C-reactive protein (CRP), serum ferritin, D-dimer, Lactic acid dehydrogenase (LDH) and interleukin-6 (IL-6) have been linked to play a role in the causation of severity and mortality in patients with COVID-19.

The disease progression is fraught with uncertainties because the risk of severe COVID-19 is not consistent among all patients. COVID-19 disease affects people in different ways. Some patients may not even notice any major clinical signs prior to clinical deterioration, although High resolution computed tomography (HRCT) can detect them at an early stage. As a result, when clinical symptoms are unclear or sparse, HRCT has been demonstrated to be a beneficial technique in diagnosing patients with COVID-19. It has been noticed that inflammatory responses play an important role in the progression of COVID-19. Inflammatory responses produced by SARS-CoV-2 viral replication and cellular destruction can recruit macrophages and monocytes and cause release of cytokines and chemokines. They eventually attract immune cells and trigger immunological responses, resulting in cytokine storm and aggravating the condition. It has been observed that COVID-19 patients have high levels of inflammatory cytokines associated with more severe disease and pulmonary inflammation, lung damage and multiple organ failure,1 and they have been reported to be predictors of mortality in patients with COVID-19.² Inflammatory markers such as serum ferritin, CRP, D-dimer, and interleukin-6 have been linked to an increased risk of developing severe COVID-19. Hence this study was conducted to determine the role of inflammatory markers and CT severity score in predicting the clinical outcomes of the patients.

Material and Methods

The present study was a retrospective study based on the data obtained from the health records of 100 adult patients who were admitted to Khaja Banda Nawaz Teaching and General Hospital, Kalaburagi, Karnataka, for a period of two months (15^th April to 14^th June 2021). All patients aged over 18 years with a confirmed positive SARS-COV2 RT- PCR report was included in the study. Pregnant women or breast-feeding mothers and patients suffering from other inflammatory conditions such as SLE, rheumatoid arthritis, inflammatory diseases, osteomyelitis, and malignancy were excluded from the study.

Around 5 mL of blood was collected to assess inflammatory markers such as serum CRP by immunoturbidimetry, serum ferritin by chemiluminescent immunoassay, LDH by International Federation of Clinical Chemistry (IFCC) method, D-dimer by immunochromatography and IL-6 by turbidimetry method. High-resolution computed tomography of the thorax was used for assessing disease severity scores.

Study design

It was a retrospective study. Patients were categorized as survivors and non-survivors based on their final mortality results. Of the total 100 patients recruited, 67 patients were survivors and 33 were non-survivors (deceased). The study tools included inflammatory markers such as serum CRP, Ferritin, D-dimer, LDH, IL-6, and imaging findings (CT severity score) which were acquired from the medical records. CT severity score (CTSS) is a semiquantitative scoring method used to estimate the severity of lung parenchyma involvement. The scoring system was adopted from Fenj Pan and Tianhe Ye's study.³

Statistical methods

All the data obtained was entered in Microsoft Excel. The data were analyzed using Statistical Package for Social Sciences (SPSS) software ver. 21.0. Categorical variables such as gender, patient’s co-morbid conditions were expressed in numbers. Continuous variables such as age, inflammatory mediators were presented as mean ± SD and median. Quantitative variables such as inflammatory mediators in COVID-19 were compared using Mann Whitney test between two groups of survivors and non-survivors. The test was performed to evaluate the association of such parameters with disease severity and mortality. It was considered statistically significant when p-value was less than 0.05.

Results

This study included 100 COVID-19 RT-PCR- confirmed patients of which 60% were male and 40% were female patients. Among survivors (67), the mean age of the patients was 50.33 years while in non-survivors (33), it was 52.78 years. Among survivors, 11 patients had hypertension, eight patients had diabetes, six patients had both diabetes and hypertension and 41 patients had no co-morbidities. Among non-survivors, 13 patients had hypertension, 11 patients had diabetes and nine patients had both hypertension and diabetes (Table 1).

The blood parameters like CRP, Ferritin, LDH, IL-6 and D -dimer levels were elevated in both survivors and nonsurvivors. The mean CRP level was 60.22±45.1 mg/L in survivors and 144.8±94.7 mg/L in non-survivors with p <0.0001 which was very significant. The mean serum ferritin level was 578±376.1 ng/mL in survivors and 738.8±581.4 ng/mL in non-survivors which was significant (p 0.0013). The mean serum IL-6 level was

179.2±145.1 pg/mL in survivors and 278.7±103.3 pg/ mL in non-survivors which was significant (p=0.0001). The mean serum LDH level was 462.4±276 U/L in survivors and 819.5±503.6 U/L in non-survivors which was significant (p <0.0006). The mean D-dimer level was 604.3±508.8 ng/mL in survivors and 1346±1002 ng/mL in non-survivors which was very significant (p <0.0001). The CT severity score in survivors was 12.3±4.9 and in non-survivors was 15.96±6.5 which was significant with p 0.0037 (Table 2).

Discussion

COVID-19 may progress from an asymptomatic stage to a severe disease. It has been observed that patients with severe disease can have systemic manifestations like acute respiratory distress syndrome, respiratory failure, multi-organ failure, and sepsis. Elderly adults, particularly those with underlying co-morbidities, had a higher risk of acquiring severe disease. This difference can be explained in part by the fact that elderly individuals have decreased innate and adaptive immunity. In healthy adults, innate immunity manages to eliminate the virus early in the disease, preventing it from reaching the alveoli. The case is different in elderly patients, in whom innate immunity has declined. The virus can enter the alveoli and replicate in large numbers. Immunity activates excessive inflammatory reactions in which pro-inflammatory cytokines are increasingly released in response to microbial infection resulting in tissue injury with a poor prognosis. This is referred as cytokine storm4 and cytokine storm has been attributed to be a major cause of death in patients with severe COVID-19.⁵

In the present study, a total of 100 patients were further categorized as survivors (n=67) and non-survivors (n=33). The mean age of the survivors was 50.33 years and non-survivors was 52.78 years. In the study conducted by Parimoo A et al., the mean age of nonsurvivors was higher than the mean age of survivors (55.67±17.41 years vs 49.50±15.36 years).⁶ Similar to other studies, COVID-19 impacted men more compared to women.^7,8 This may be related to the higher prevalence of comorbidities in men. Furthermore, the number of male patients admitted to the hospital in the present study was significantly larger (60%) than the number of female patients (40%) which could be a confounding factor. Co-morbidities were present in 26 patients among survivors and 33 patients among non-survivors. The common co-morbidity was hypertension (24%), followed by diabetes (19%), while 15% of patients had both hypertension and diabetes. Among survivors, 11 patients had hypertension and among non-survivors 13 patients had hypertension. In a study by Parimoo A et al., among the non-survivors, 31 (56.36%) patients had hypertension while amongst the survivors, 27 (31.03%) had hypertension, and this difference amongst the two groups was statistically significant (p=0.003).⁶ In the study conducted by Bhandari et al., among 80 patients, most of the patients were in their fifth and sixth decades of life with a mean age of 50.40 years. The males were more commonly affected than females (59% males and 41% females). The most prevalent co-morbidity was diabetes mellitus (56%) followed by hypertension (48.83%).⁹

C-reactive protein (CRP) is a protein produced in the liver that functions as an indicator of acute inflammation. It is commonly elevated in infections and autoimmune diseases due to an inflammatory response and potential tissue damage. It also serves as a predictor of the severity of cardiovascular disease. The recent COVID-19 pandemic also demonstrated that CRP is elevated during the active phase of infection. In our study, CRP was elevated both in survivors and non-survivors but non-survivors had comparatively higher values than survivors. The mean C-reactive protein in non-survivor group was 144.8± 94.7 mg/L with a statistical significance of p <0.0001, while the mean C-reactive protein in survivors was 60.22± 45.1 mg/L. In another study, the median CRP level among non-survivors was 102.45 mg/L (2.3, 342.1) and 37.94 mg/L (0, 404.1) among survivors and it was statistically significant (p <0.001). The median CRP level before the terminal event (survival or death) among non-survivors was 116.8 mg/L (10.5, 426) and 14.38 mg/L (0, 374.2) among survivors and this difference was statistically significant (p <0.001).6 Findings of the study by Smilowitz NR also indicated that elevated CRP levels had a direct correlation with severity and mortality.¹⁰

Ferritin is an intracellular iron-storing protein that plays a key role in inflammatory illnesses such as infection, cancer, and neurodegeneration. High circulating ferritin is detected in critical disorders as a hallmark of Hyper Ferritin Syndromes. Raised serum ferritin has been observed to be a significant predictor of severe SARSCoV2 infection and higher serum level was associated with increased mortality. In the present study, the mean serum ferritin level in survivor group was 578±376.22 ng/ mL and in non-survivor group was 738.8±581.4 ng/mL with p value 0.0013. In the study conducted by Ahmed S et al., the median ferritin value was 1096.4 ng/mL in the non-survivor group, which was highly significant as compared to survivors 548.9 ng/mL (p value = 0.02) and was found to be an independent predictor of mortality.⁷ In the study by Parimoo A et al., the median ferritin level at baseline among non-survivors was 1009 ng/ mL (69.2, 7580) and 659 ng/mL (25.93, 5237) among survivors and this difference was statistically significant (p <0.001).⁶ Our results were similar to the findings of these studies and patients with elevated ferritin levels had a higher mortality rate than those with lower ferritin levels. Hence, an elevated ferritin level can be utilized as a biomarker to differentiate high-risk from low-risk patients of COVID-19. The test could assist in the early detection of disease progression and initiation of treatment.

LDH has traditionally been utilized as a biomarker of cardiac damage. Since LDH is present in lung tissue (isozyme 3), patients with severe COVID-19 can be predicted to have higher levels of LDH in their blood, as the condition is characterized by a severe type of interstitial pneumonia that frequently progresses to acute respiratory distress syndrome. Nuramin et al., in their study found a significant difference between the mean LDH levels in severe COVID-19 compared to nonsevere COVID-19 (1006±601.77 vs 543.5±480.41, p <0.001).¹¹ In our study, the level of LDH in the nonsurvivor group was higher than the survivor group (819.5±503.6 vs 462.4±276 U/L) with a statistically significance of (p=0.0006). Zeng Z, Yu H et al. revealed that LDH >400 U/L on admission were independently associated with disease severity in patients with COVID-19.¹² As LDH level indicates multiple organ injury and failure, it may play a more prominent role in this pathology in impacting clinical outcomes in COVID-19 patients.

IL-6 is an inflammatory cytokine which controls the immune response and is thought to be the cause of the clinical symptoms after severe disease. Subjects with SARS-CoV-2 had high levels of IL-6 that were correlated with patient symptoms including pulmonary inflammation and extensive lung damage. Therefore, the control of IL-6 synthesis and secretion may be important to inhibit progression of disease. In our study, IL-6 was less elevated in survivor patients (179.2±145.1 pg/mL) than non-survivors (278.7±103.3 pg/mL) with a statistical significance of p=0.0001 which indicated severity of disease and implied risk of mortality. In a study conducted by Parimoo A et al., the median IL-6 level among non-survivors was 53.84 pg/mL compared to survivors 37.94 pg/mL with p=0.007.⁶ In the study by Bahram Nikkho et al., out of 208 patients, 107 had elevated IL-6 levels which significantly increased the duration of hospital stay (p=0.02). The frequency of ICU admission (p=0.04) and mean of ICU stay (p=0.8) were also higher in elevated IL-6 group. The death occurrence among patients with elevated IL-6 was 3.91 times higher.¹³ The other study also reported elevated IL-6 levels in severe SARS COV-2 infection with high mortality.¹⁴ Zeng Z, Yu H et al., observed that the patients who had IL-6 >50 pg/mL on admission were independently associated with disease severity.¹²

Coronavirus promotes endothelial inflammation and damage, which leads to diffuse intravascular coagulation. Patients with D-dimer levels greater than 1 mg/L have an undesirable disease progression. Elevated D-dimer levels in patients with severe illness may indicate an underlying impaired blood coagulation function. In our study, D-dimer elevation in non-survivor group (1346±1002 ng/mL) was more evident with significance of p <0.0001 than that of survivor group (604.3±508.8 ng/ mL). In the study conducted by Tang N et al., survivors had 0.61 µg/mL (0.35-1.29) D-dimer level as compared to non-survivors who had 2.12 µg/mL (0.77-5.27) with p <0.001. Arachchillage DRJ, in his study found that out of 84 patients who developed Acute respiratory distress syndrome (ARDS), 52.8% (44/84) patients died and these patients had significantly higher D-dimer levels [median (interquartile range)] 3.95 µg/mL (1.15 -10.96) compared those who survived (0.49 µg/mL (0.31 -1.18), with p value 0.0013.15 Hence markedly elevated D-dimer may be used to guide therapy and evaluate prognosis.

Where RT-PCR testing is not available, and where test results are delayed, or where there is a clinical suspicion of COVID-19 despite initial negative RTPCR testing, WHO recommended using chest imaging as part of the diagnostic workup for COVID-19 disease. COVID-19 disease can present abnormalities ranging from asymptomatic-to-severe respiratory distress symptoms and death. The virus causes direct lung injury, creating inflammatory changes in the alveolar wall, restricting oxygen exchange and leading to severe respiratory distress, pulmonary fibrosis, and mortality. The chest computed tomography (CT) scan is a useful tool for identification of pulmonary changes, screening, diagnosis, and clinical classification of patients suspected of infections. In our study, the mean CT severity score was 15.96±6.5 in non-survivors and 12.3±4.9 in survivors which was significant with p value 0.0037. In another study, the mean CTSS of non-survived cases was significantly higher (13.68±4.59 versus 8.72±4.42; p <0.0001).¹⁶

The present study signified a positive association between disease severity and CTSS. Studies conducted by Bhandari et al.,⁹ Yang et al.,¹⁷ and Saeed et al.,¹⁸ have also noted similar findings regarding the accuracy of CT severity score in evaluating the disease severity and mortality.

Conclusion

The disease severity of COVID-19 was correlated with D-dimer and CRP levels. CTSS was also significant in diagnosing severity of the disease. They had the diagnostic accuracy in predicting the severity of the disease and mortality. The patients with severe form of COVID-19 infection also had raised levels of IL-6, LDH and ferritin. Patients with co-morbidities had higher levels of inflammatory markers and exhibited severe disease.

Conflict of Interest

Nil

Financial Support

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