Introduction

Acute ischemic stroke (AIS) is one of the most prevalent causes of mortality and disability; moreover, it imposes a considerable economic and social burden (1). The most common subtype of stroke is ischemic stroke (2). Endovascular treatment (intraarterial thrombolysis, mechanical thrombectomy, etc) and intravenous thrombolytic treatment (IVT) are the most frequently employed treatments for AIS (3). However, some complications occur with recanalization (cerebral hemorrhagic transformations, brain edema and reoclusion, etc). These complications affect mortality and functional status (4).

Platelet activation and aggregation is important in the pathogenesis of AIS. Platelet aggregation induces thrombosis and vascular occlusion. Thus, clinical conditions (such as ischemic stroke and myocardial infarction) occur (5). The immune response is critically important and starts after stroke. Serum leukocytes pass into the cerebral anoxic tissue following disruption of the blood-brain barrier. Neutrophils and lymphocytes are recruited to this area, and the immune response begins with cytokines. Thus, platelets and coagulation factors increase, and the ischemic area expands (6,7).

Blood tests are performed routinely before IVT in patients with AIS (especially hemogram and coagulation tests). The platelet/lymphocyte ratio (PLR) is a more stable test than individual tests for platelets and lymphocytes. It is an easily accessible, inexpensive, and routine test (8). Recent studies have confirmed that the PLR can be used for myocardial infarction, ischemic stroke, pulmonary embolism, and peripheral ischemia (9-11).

In this study, we aimed to determine serum platelet and lymphocyte levels, calculate the PLR value, and evaluate its relationship with in-hospital mortality, cerebral hemorrhagic transformation, and short-term prognosis in patients with stroke treated with intravenous thrombolysis.

Methods

Ethics and Patient Population

The study was approved by University of Health Sciences Turkey, Konya Training and Research Hospital Ethic Committee (approval number: 38-16, date: 08/05/2020). The principles of the Declaration of Helsinki and Guidelines for Good Clinical Practice were adhered to during the study.

The data were collected retrospectively. The study population included AIS patients who were hospitalized and treated with IVT. The purpose and probable complications of IVT were described. Patients or their relatives signed an informed consent form prior to inclusion in the study. Informed consent was obtained from all patients and/or their relatives routinely before IVT. Some diseases (that could affect the study data) were excluded (Table 1). Patients were questioned about their age, gender, and any chronic diseases they might have (hyperlipidemia, hypertension, diabetes mellitus, etc). Initial symptoms were grouped as consciousness, sensory, hemi/mono-paresis, cerebellar, and others (cranial neuropathy, dysarthria/aphasia, dysphagia, convulsion, cortical blindness, delirium).

The data were collected from patients hospitalized in the neurology clinic between January 2013 and March 2020. Three hundred twenty AIS patients treated with IVT were included in the study. However, 70 patients were excluded from the study due to comorbid diseases and missing data. The data on 250 AIS patients were included.

Definition of the Treatment Period

The treatment was administered according to AIS early treatment management recommendations of the American Heart Association/American Stroke Association (3). Before treatment, diagnosis of ischemic stroke and affected vascular areas were confirmed by brain computed tomography (CT) and cerebral CT angiography. Vascular occlusions were divided into two groups, anterior and posterior. If treatment was not contraindicated, alteplase (0.9 mg/kg, maximum 90 mg) was started (10% in 1 minute, the remaining dose in 1 hour, intravenously). If the neurological examination was disrupted after treatment, brain CT was immediately performed. Otherwise, brain CT was routinely performed at the 24^th and 72^nd hours after treatment. As a result of these neuroimaging studies, intracerebral hemorrhage was evaluated. Patients were divided into two groups (cerebral hemorrhagic transformation positive or negative).

Disability was scored before treatment using the National Institutes of Health (NIH) stroke scale (12). A decrease (between discharge and baseline) of five points or more of the NIH stroke scale score was accepted as clinical improvement. All other patients were scored as “no clinical improvement”. Mortality was calculated.

Blood Tests

Blood samples were obtained before IVT from the antebrachial vein. Hemogram was tested with an Automated Blood Cell Analyzer (Pentra 120 Retic Hematology Analysis Device, ABX, Montpellier, France). Platelet and lymphocyte results were obtained from the hemogram test. After the test, PLR was calculated using the formula “PLR=platelet count/lymphocyte count”.

Statistical Analysis

Data were analyzed with SPSS^® version 17.0 statistical package software (SPSS Inc., Chicago, IL, United States). Mean ± standard deviation and median (minimum-maximum) values were used to summarize numerical data. Categorical data were summarized as number (n) and percentage (%). Categorical data were compared with a chi-square test or Fisher’s exact test. The distribution of the data was evaluated with Kolmogorov-Smirnov and Shapiro-Wilk tests. Comparisons of numerical data between two groups were performed with a Student’s t-test or a Mann-Whitney U test (according to the data distribution). The cut-off point for the PLR was calculated according to receiver operating characteristic (ROC) curve analysis. The cut-off point was determined according to the sensitivity and specificity values. The area under the curve (AUC) was calculated. The 95% confidence interval (95% CI) was determined. The relationship between numerical data was evaluated with the Spearman correlation test. Correlation coefficients were defined as follows: 0-0.25 weak, 0.25-0.50 weak-medium, 0.50-0.75 strong, and 0.75-1.00 very strong correlation. Results were considered statistically significant at p<0.05.

Results

General Results

Two hundred fifty patients [128 (51.2%) female and 122 (48.8%) male] treated with IVT were included in the study. The mean age was 72.88±12.39. The most common initial symptom was hemi/mono-paresis (n=211, 84.4%). Ischemia was detected especially in the anterior vascular areas (n=205, 82.0%). Hypertension was the most common chronic disease (n=167, 66.8%). Patients demographic characteristics and blood values are summarized in Table 2.

Clinical improvement was higher in patients with a high NIH stroke scale score (p<0.001). Also, mortality and hemorrhagic transformation were higher in these patients (p<0.001, p=0.009). Patients treated with IVT in less than 3 hours had better clinical improvement (p=0.042). There was no difference in hemorrhagic transformation or mortality between treatment time groups (p>0.05). The mean age of patients with clinical improvement was lower [74.17±11.35 (43-95) and 69.95±12.87 (35-95)]. Blood values of all patients were serum platelet (10³/mm³) level 245.49±80.83 (107-559), lymphocyte (10³/mm³) level 2.10±0.89 (0.56-6.87), and PLR value 136.59±78.38 (24.16-622.35).

The Association of PLR Levels with Initial Disability

Patients were compared in two groups according to disability score before IVT (mild disability = NIH stroke score <15, severe disability = NIH stroke score ≥15). There was mild disability in 162 (64.8%) patients and severe disability in 88 (35.2%) patients. The PLR was higher in patients with severe disability (p<0.001) (Figure 1). The serum lymphocyte level was lower in the group with severe disability (p<0.001). There was no difference in the platelet level between the two groups (p=0.236). The platelet, lymphocyte, and PLR values of the groups are summarized in Table 3A. A negative correlation was detected between the NIH stroke score and the lymphocyte level (p=0.026, r=-0.48). There was a positive correlation with the PLR level (p=0.001, r=0.59).

In ROC analysis, the PLR cut-off value was calculated as 121.72 with 62.5% sensitivity and 61.0% specificity (p=0.000, AUC: 0.651, 95% CI: 0.58-0.72) (Figure 2). The lymphocyte cutoff value was calculated as 1.86 with 66% sensitivity and 65% specificity (p=0.000, AUC: 0.694, 95% CI: 0.62-0.76).

The Association of PLR Levels with Clinical Improvement

Patients were divided into two groups according to the difference in the NIH stroke scale, and the groups were compared. There was clinical improvement in 136 (54.4%) patients and not in 114 (45.6%). There was no statistically significant difference between the degree of clinical improvement and the PLR (p=0.072). The serum lymphocyte level was higher in patients in the group with clinical improvement (p=0.023). There was no difference between groups in the serum platelet levels (p=0.390). The platelet, lymphocyte, and PLR values of the groups are summarized in Table 3B.

In ROC analysis, the lymphocyte cut-off value was calculated as 1.95 with 56.6% sensitivity and 54.4% specificity (p=0.023, AUC: 0.584, CI: 0.51-0.65).

The Association of PLR Levels with In-hospital Mortality

The in-hospital mortality rate was 12.4% (n=31). The PLR was higher in patients with mortality (p<0.001) (Figure 3). Serum lymphocyte levels were lower in these patients (p=0.001). There was no between-group difference in platelet levels (p=0.236).

In ROC analysis, PLR cutoff value was calculated as 131.43 with 61.3% sensitivity and 63.0% specificity (p=0.001, AUC: 0.668, CI: 0.58-0.79) (Figure 4). The lymphocyte cut-off value was calculated as 1.66 with 68.8% sensitivity and 67.7% specificity (p=0.000, AUC: 0.735, CI: 0.63-0.83).

The Association of PLR Levels with Hemorrhagic Transformation

The hemorrhagic transformation rate was 10.8% (n=27). The serum platelet level was lower in patients with hemorrhagic transformation (p=0.024) (Figure 5). There was no difference between the lymphocyte level and PLR in these patients (p=0.156, p=0.675). The platelet, lymphocyte, and PLR values of the groups were summarized in Table 3D.

In ROC analysis, the platelet cut-off value was calculated as 211.0 with 67.7% sensitivity and 63.0% specificity (p=0.024, AUC: 0.633, CI: 0.51-0.75) (Figure 6).

Discussion

This is the second study in the literature to evaluate the relationship between mortality, disability, and the PLR in AIS patients treated with IVT (13). In our study, the cut-off point was hospital discharge time. In another study, the 90 day prognosis and mortality were evaluated.

Lymphocyte and platelet levels are important in the pathogenesis and prognosis of ischemic vascular diseases (especially ischemic stroke and myocardial infarction). Increased platelet levels and decreased lymphocyte levels are associated with severe disability and poor prognosis in ischemia (14-17). Overactivation of platelets during ischemic stroke causes thrombosis and vascular occlusion (18). In this process, increased stress activates the hypothalamus-pituitary-adrenal glands. As a result of increased cortisol, the lymphocyte concentration is partially reduced (19). In our study, the lymphocyte level was lower in groups with high initial disability and mortality. This result suggested that the lymphocyte level may be related to prognosis and disability in stroke patients treated with IVT.

The relationship of the PLR with ischemic vascular diseases has been reviewed in the literature. As the PLR increases, the risk of peripheral vascular occlusion increases. In addition, PLR is associated with occurrence of vascular events (11,20). The PLR has been shown to be an independent predictor of cardiovascular disease recurrence and in-hospital mortality in patients with acute myocardial infarction (21,22). In stable angina pectoris, the PLR is higher in patients with decreased coronary collateral flow (23). Regarding the ischemic stroke-PLR relationship, an increased PLR is an independent predictor of stroke (24). A higher PLR is associated with increased cerebral ischemia volume and poor recanalization in patients with ischemic stroke treated with endovascular mechanical thrombectomy. In addition, an increased PLR is associated with postoperative stroke risk and depression after carotid endarterectomy (25,26).

In an earlier study, investigating the PLR in AIS patients treated with IVT, blood samples were drawn within the first 24 hours after symptom onset, and patients were evaluated after 3 months. The PLR was higher in patients with unfavorable outcomes. After 3 months, 38 (13.3%) of these patients died. The PLR was higher in these patients. In conclusion, a high PLR in this study was associated with unfavorable outcomes and death in patients with ischemic stroke treated with IVT (13). Platelet and lymphocyte values can be affected by IVT. Therefore, we obtained blood samples before treatment. In our study, a high PLR was associated with increased in-hospital mortality and a high initial disability scale score. There was no relationship between short-term clinical improvement and the PLR. In our study, clinical improvement was evaluated between the pre-discharge and hospitalization period. The relationship with long-term clinical improvement could not be evaluated.

The immune response begins rapidly after ischemic stroke. This is especially associated with disruption of the blood-brain barrier structure. Lymphocytes and platelets are blood cells that actively participate in this process, and they are associated with the severity of stroke (5-7). The lymphocyte value is a predictive marker for microvascular occlusion (27,28). A low platelet level is associated with increased symptomatic intracerebral hemorrhage in patients with ischemic stroke treated with IVT. The risk of hemorrhagic transformation is higher in thrombocytopenic patients. However, no relationship has been detected between poor outcome risk, mortality, and PLR (29). In our study, the lymphocyte value was lower in patients who died. A low lymphocyte level was associated with increased in-hospital mortality. The lymphocyte cut-off value was calculated as 1.66 with 68.8% sensitivity and 67.7% specificity for mortality. A low platelet level was associated with hemorrhagic transformation. The platelet cut-off value was calculated as 211.0 with 67.7% sensitivity and 63.0% specificity for hemorrhagic transformation. There was no relationship between the PLR and hemorrhagic transformation.

Study Limitation

This study had several limitations. First, it was a retrospective study conducted in only one center. Second, the number of patients included in the study was limited. Third, the difference in PLR (before and after treatment) could not be calculated, and its relationship with prognosis could not be determined. Fourth, the relationship of chronic diseases with the PLR and prognosis could not be evaluated.

Conclusion

In blood tests before IVT treatment in AIS patients, a low lymphocyte level is associated with the initial severity of stroke disability. Also, a low platelet level is associated with hemorrhagic transformation. A higher PLR is associated with high initial disability and in-hospital mortality. The PLR may be an inexpensive, easily accessible, and effective marker for evaluating stroke severity and predicting mortality.

Ethics Committee Approval: The study was approved by University of Health Sciences Turkey, Konya Training and Research Hospital Ethic Committee (approval number: 38-16, date: 08/05/2020).

Informed Consent: Informed consent was obtained from all patients and/or their relatives routinely before IVT.

Peer-review: Externally peer-reviewed.

Authorship Contributions: Surgical and Medical Practices - F.E., A.D.; Concept - F.E., A.D., G.E.; Design - F.E., A.D., G.E.; Data Collection or Processing - F.E., A.D.; Analysis or Interpretation - F.E., G.E.; Literature Search - F.E., G.E.; Writing - F.E., A.D., G.E.

Conflict of Interest: No conflict of interest was declared by the authors.

Financial Disclosure: The authors declared that this study received no financial support.