This study was designed to assess the predictive value of lipid-to-neutrophile ratios for the short-term survival of patients with PTE. Based on our findings, cholesterol/neutrophil, LDL/neutrophil, and HDL/neutrophil ratios were found to be appropriate predictive factors in PTE patients.
PTE has an incidence rate of approximately 60–70 per 100,000, among the general population and if untreated, its mortality can be as high as 30% [15–17]. Because most PTE patients ultimately die within the first hours of presentation, early diagnosis and having an insight into its possible prognosis are of paramount importance [18]. Few scores are used to determine the prognosis of PTE patients like PESI and simplified PESI score, Geneva score, and 2014 European Society of Cardiology (ESC) mode, however recent studies indicate that the Geneva risk score and 2014 ESC model are not reliable to identify the high-risk PTE patients. Moreover, although the PESI score can be reliable for identifying the low risk of early mortality in PTE patients, clinicians still question its ability to identify the high risk of early mortality in them [19–21]. Recent studies have indicated several laboratory parameters including brain natriuretic peptide (BNP), N-terminal-proB-type Natriuretic Peptide (NT-proBNP), interleukin (IL)-6, IL-8, heart-type fatty acid binding protein (H-FABP), troponin and myoglobin as a possible prognostic factor for PTE patients [16, 17], however, accessibility, availability, and cost-effectiveness limit their use in the clinical practice. In this condition, the widely available and accessible parameters such as CBC. diff findings and lipid profile are suggested as an appropriate predictive factor for mortality in PTE patients. Studies have reported ratios like monocytes to HDL ratio or neutrophil to lymphocyte ratio as probable prognostic factors for PTE [22, 23]. This study founds cholesterol/neutrophil and LDL/neutrophil, and HDL/neutrophil ratios appropriate predictive factors for IHM in PTE patients.
Recently, a new concept called “lipid paradox” has been introduced which means that a lower rate of lipid parameters like serum total cholesterol, LDL, and TG have a significant relationship with a higher rate of IHM in cardiovascular diseases like acute coronary syndrome and myocardial infarction [24]. From the pathophysiological point of view, the basis of the thrombotic process is inflammation leading to oxidative changes that can decrease cholesterol synthesis. Also, acute-phase reactants can increase cholesterol uptake by hepatocytes [25, 26]. In addition, recent studies on mice have shown that HDL and Chol have an important role in lung normal function and have a vital role in the regulation of pulmonary inflammatory response after tissue injury [27, 28]. On the other hand, HDL can protect endothelial cells against inflammation and oxidative stress by preventing monocyte flow to the arterial wall, which reduces the expression of CD11b on monocyte and endothelial molecules and prevents the adhesion of monocytes to the endothelial wall [29–31]. Finally, TGs are known as important energy sources for peripheral organs. An increase in acute phase reactions increases the function of lipoprotein lipase that breaks down circulating TGs and results in lower TG levels [32]. In a study by Karatas et al. serum total cholesterol, LDL, HDL, and TG levels were significantly lower in deceased patients when compared to the surviving PTE patients [12]. In another study by Avci et al., serum levels of HDL were also significantly lower in deceased PTE patients [22]. In this study also the Serum total cholesterol, LDL, HDL, and TG levels were significantly lower in PTE patients who died during their hospitalization.
On the other hand, studies indicate that leukocyte count could be related to fibrinogen, factor VII, and factor VIII levels and can cause local thrombogenic activity [33, 34]. Moreover, stimulated neutrophils may be responsible for vascular injury due to increased cytokines secretion [35], which can be a result of severe hypoxia caused by pulmonary artery obstruction and an increase in neuro-hormone and adrenergic system activity. This reaction may aggravate thrombosis and the severity of the disease in patients [36]. In a study by Kayrak et al. WBC, neutrophil, and lymphocyte counts were significantly higher in deceased PTE patients in comparison to survivors [37]. Another study by ÇAVUŞ et al. also indicates the same result [23]. In this study lymphocyte count was significantly higher in the mortality group however WBC and neutrophil count didn't have a significant difference between the death and alive groups.
Recent investigations suggested the neutrophil to HDL ratio as a prognostic factor for the severity of coronary arteries stenosis [38], clinical outcomes of patients with MI [39], and all-cause and cardiovascular mortality in the general population [40]. As one of the first tries, we investigated the relationship between lipids to neutrophil ratios and IHM of PTE patients in a great cohort and we found cholesterol/neutrophil, HDL/neutrophil and LDL/neutrophil ratios good predictors of short-term survival in PTE patients. Some limitations may affect our findings. One of them is the retrospective design of the study and the second one is the lack of long-term follow-up in the study. Also, its recommended to compare the suggested ratios in this study with other risk scores such as PESI in future studies. In addition, there is a need for future prospective multicenter studies to provide a higher level of evidence in this regard.