The effect of smoking on COVID‐19–linked biomarkers in hospitalized patients with COVID‐19

Abstract Background The coronavirus pandemic, an infection (coronavirus disease 2019—COVID‐19), caused by severe acute respiratory disease coronavirus 2 (SARS‐CoV‐2), continues to have a strong influence worldwide. Although smoking is a major known risk factor for respiratory infectious disease, the effects of smoking on COVID‐19 are unclear. In this study, we aimed to evaluate the relationship between smoking and important hematologic (lymphocyte count, neutrophil count, platelet count, neutrophil‐lymphocyte ratio [NLR], platelet‐lymphocyte ratio [PLR]), inflammatory, and biochemical biomarkers in the prognosis of hospitalized patients with COVID‐19. Methods In a COVID‐19 pandemic hospital between June and August 2020, 200 adult patients aged over 18 years were hospitalized with COVID‐19 inflammatory and hematologic biomarkers at their first admission and smoking data were selected for this study. Results The rate of smokers was much higher among men (91.5%) than in women (8.5%) (p = 0.001). Neutrophil counts were evaluated and was significantly higher in current smokers (p < 0.001) and ex‐smokers (p = 0.001), and NLR (p = 0.008) and ferritin (p = 0.004) levels were higher than in never smokers. The saturation of patients had a negative significant linear correlation of NLR, PLR, and pack years of smoking. Compared with never smokers, current smokers had higher neutrophil counts (OR = 0.828 [0.750–0.915]; p = 0.041), NLR values (OR = 0.948 [0.910–0.987]; p = 0.009), and CRP levels (OR = 0.994 [0.990–0.999]; p = 0.019). Conclusion Serum neutrophil, NLR, and ferritin levels, which are widely used in determining the prognosis of COVID‐19, were found higher in current smokers/ex‐smokers. These results support the view that a poor prognosis of COVID‐19 is associated with smoking.


| INTRODUC TI ON
The new type of coronavirus, severe acute respiratory disease coronavirus 2 (SARS-CoV-2, which caused the coronavirus disease 2019  pandemic), is an infectious respiratory disease that continues to be the most important health problem, threatening the whole world. Upto June 23, 2021, a total of 178,202,610 cases had been confirmed, including 3,865,738 deaths, and the mortality rate was 4.76%. 1 The infection usually begins with flu like symptoms. 2 The most frightening aspect of COVID-19 is its life-threatening consequences, from mild self-limiting illness to severe pneumonia, acute respiratory distress syndrome, septic shock, and systemic multi-organ failure syndrome. Based on the information available so far, they argues that the PCR test is the most reliable diagnostic method in diagnosing COVID-19. 3 However, about 75% of the patients with positive RT-PCR throat swab tests are asymptomatic. 4 Therefore, it is needed reliable biomarkers for rapid diagnosis and treatment of COVID-19.
Although some biomarkers associated with COVID-19 progression have been identified, there is still no consensus. 5,6 Urgent identification of clinical laboratory predictors of disease progression toward a severe/critical form is an urgent necessity for physicians to be able to stratify risks, distinguish and differentiate patients with severe COVID-19 from those with mild/moderate forms.
Former/current smoking increases the risk of respiratory viral 7,8 and bacterial 9 infections. This was also experienced in the Middle East respiratory syndrome (MERS) outbreak 10 and was associated with worse outcomes for those infected. However, the influence of smoking on COVID-19 and prognosis is controversial. Some authors stated that the prevalence of cigarette smoking in patients with COVID-19 was lower than in the general population, 11-13 others found no significant association between smoking and increased risk of developing severe COVID-19. 14,15 Although there is no mechanism to explain how this might happen, some studies hypothesized that the intake of nicotine in cigarettes might reduce the likelihood of developing COVID-19 by smokers. 12,14,16 However, it has also been concluded that smoking was most likely associated with increased severity and poorer outcomes of COVID-19. 11,17 Interleukin (IL)-6 is emphasized as the most effective biomarker in determining the severity of COVID-19. 18 28 and thyroid malignancy. 29 In addition, the importance of the neutrophil-the lymphocyte ratio (NLR) and platelet-lymphocyte ratio (PLR), which are increasingly important in showing the prognosis in inflammatory diseases in the evaluation of COVID-19 severity has been emphasized in several studies. 5,30,31 Although many studies are exploring the effects of smoking on hemogram parameters, there is a limited number of studies on the effects of smoking on NLR and PLR ratios in patients with COVID-19.
The aim of our study was to investigate the effects of smoking on the diagnosis of COVID-19, and NLR and PLR.

| Study design and participants
The study was performed in accordance with the Declaration of

| Data collection
Clinical data at first admission include demographic information

| Smoking status
Smoking status was categorized as never smoker, ex-smoker, or current smoker. The total amount of cigarettes was found by multiplying the daily smoked packs by the total years of smoking (pack-year).

| Statistical analysis
All analyses were performed with commercially available statistical software (SPSS v. 22). Participants were categorized according to their reported smoking status at the time of participation in the study. Differences between qualitative variables were analyzed using the Chi-square test. Differences in the quantitative variables among non-normally distributed variables were analyzed using the Mann-Whitney U test and are presented as the median (min-max).

The comparison method of the variables with normal distribution
were analyzed using independent samples T test (Mean ± SD).
One-way analysis of variance (ANOVA) was used for the intergroup comparison between the current smoking, ex-smoking, and never smoking groups. Pearson's correlation coefficient was used to measure the correlation between variables. An ordinal logistic regression model was used. The smoking variable was modeled as never smoking, ex-smoking, and current smoking. Statistical significance, p < 0.05 value was chosen.

| RE SULTS
The study population was stratified by smoking status as described in Table 1. Study patients had an average age of 64.9 years and 56.8% were male. The vast majority of patients who were current smokers and ex-smokers were men, and patients who were current smokers constituted a relatively younger population (p = 0.01, Table 1). The rates of comorbid disease were found as follows: diabetes (n = 99, 53.51%), hypertension (n = 111, 60%), and other comorbidities (n = 55, 29.7%). BMI and comorbid diseases were not associated with smoking status. In this study, 162 (87.57%) of the patients were polymerase chain reaction (PCR-RNA) positive. Fifty (72.03%) of these patients were current smokers, 53 (28.65%) were ex-smokers, and 82 (44.32%) were never smokers. Neutrophil values evaluated at the first admission were significantly higher in current smokers (p < 0.001) and ex-smokers (p = 0.001) than in never smokers; however, there was no difference between current smokers and ex-smokers (p = 0.375). Ferritin values were significantly higher in current smokers than in ex-smokers and never smokers. NLR was significantly higher both in current smokers (p = 0.02) and ex-smokers (p = 0.03) than in never smokers; however, there was no difference between current smokers and ex-smoking  (Table 3).

| DISCUSS ION
The risks associated with smoking and COVID-19 are somewhat unclear. However, several recent publications reported that smokers were under-represented among hospitalized patients with COVID-19. 33 In the present study, we aimed to investigate the effect of smoking on prognostic factors to evaluate the effect of smoking on prognosis in patients with severe COVID-19. This is the first study to evaluate the effect of smoking on prognostic inflammatory biomarkers associated with COVID-19 in hospitalized patients. We obtained some important data showing that smoking significantly affected the prognostic parameters for this disease.
It is widely accepted that smoking is a risk factor for the progression of COVID-19. [34][35][36][37] Smoking is well-established as harming lung health and causing smokers to become more prone to infectious pathogens. In a study involving a large cohort of 1099 patients with  To date, studies have proven that in severe cases, lymphocyte and platelet counts decrease, but neutrophil counts, CRP, NLR, and PLR values increase. 20,43 NLR and PLR, which are easily obtained from a serum complete blood count, are widely used to predict mortality and prognosis in other bacterial and viral pneumoniae. 43 In the present study, the prognostic parameters including neutrophil counts and NLR of patients who smoked and ex-smokers were higher than those of patients who never smoked. Moreover, it showed that continuing to smoke and higher cigarette pack years were more likely to increase these values. Therefore, patients with severe COVID-19 who smoke may have a poor prognosis. are used as an important marker in the diagnosis and prognosis of COVID-19. 16 Lee et al. 44 argued that serum ferritin levels were increased in former or current smokers and were increased relative to the amount of smoking. The present study found similar results.
However, it is unclear whether the increased ferritin value is related with COVID-19 or cigarette smoking. No evidence of a relationship was found between D-dimer, troponin, and smoking.
We have some limitations in this study. We could not compare the association between smoking and biomarkers with patients with non-severe disease because we planned our study only on hospitalized patients with COVID-19 (severe disease). In addition, we cannot predict whether the biomarkers are high in pre-disease smokers because we do not have the pre-COVID-19 parameters of the patients.

| CON CLUS ION
Our study provides evidence that some prognostic parameters including NLR and ferritin are increased in smokers according to the laboratory test results at the time of admission of hospitalized patients with COVID-19 cases. These results support the view that a poor prognosis of COVID-19 is associated with smoking.

ACK N OWLED G M ENT
We are grateful to David Francis Chapman for the language editing and to Sinan İyisoy for statistical analysis of the study.

CO N FLI C T O F I NTE R E S T
The author declare that no conflict of interest.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data in this manuscript are available.