Neutrophil precursors in complete blood count: innovative biomarker for acute pulmonary embolism severity

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RESEARCH ARTICLE

Hippokratia 2025, 29(1): 20-24

Karakurt G1, Özatak C2, Güven O3, Naser A4, Aynacı E5
1Department of Chest Diseases, Kırklareli Training and Research Hospital, Kirklareli
2Department of Emergency Medicine, Medipol University, Istanbul
3Department of Emergency Medicine, Kırklareli University, Kirklareli
4Department of Cardiology, Kırklareli Training and Research Hospital, Kirklareli
5Department of Chest Diseases, Beykent University, Istanbul
Türkiye

Abstract

Background: Inflammation plays an important role in the pathogenesis of acute pulmonary embolism (APE), which is a cardiovascular emergency associated with high mortality. The primary determinant of the clinical course in the setting of APE is right ventricular dysfunction (RVD). In this study, we aim to investigate the usefulness of circulating immature granulocytes (IG) as an inflammatory biomarker in predicting RVD in APE.

Methods: We retrospectively analyzed data of 59 patients admitted to the emergency department between January 2019 and June 2022, diagnosed with APE. A complete blood count at admission determined the IG count. According to their echocardiographic evaluation, patients were divided into two groups according to the presence of RVD.

Results: We observed in APE that the mean IG count was significantly higher in patients with RVD than those without RVD (p =0.001). The multivariate logistic regression analysis detected a significant (p =0.006) and independent effect of the IG count in distinguishing cases with and without RVD.

Conclusions: We found the discriminative effectiveness of the IG 0.05 cut-off value for RVD. IGs, an inflammatory precursor obtained readily and without additional cost as part of a complete blood count, may be a new and valuable biomarker for risk stratification and prognosis assessment by predicting RVD in APE patients. HIPPOKRATIA 2025, 29 (1):20-24.

Keywords: Acute pulmonary embolism, immature granulocytes, neutrophil precursors, right ventricular dysfunction

Corresponding author: Gökhan Karakurt, MD, Department of Chest Diseases, Kırklareli Training and Research Hospital, İstasyon Mahallesi, 28. Edirne Sokak, No 9, Kirklareli, Turkey, tel: +905532904502, e-mail: gokhankarakurt16@gmail.com

Introduction

Acute pulmonary embolism (APE) is a life-threatening cardiovascular disease usually diagnosed in the emergency department1, and APE patients face a 30-day mortality rate of over 15 %, with sudden death accounting for nearly 11 % of these fatalities2,3. Because of the high mortality rate, prompt identification and appropriate risk stratification of APE patients play an important role in clinical decision-making4. Preserved right ventricular function in APE patients carries a good prognosis with anticoagulant therapy alone, while right ventricular dysfunction (RVD) resulting from acute pressure overload is the primary determinant of early clinical course and mortality risk5,6. The risk of an unfavorable outcome is higher in high-risk APE patients presenting with systemic hypotension, cardiogenic shock, or cardiac arrest accompanied by right ventricular dysfunction4. Therefore, early identification of patients with poor prognoses may increase the survival rate.

Clinical scoring criteria such as the pulmonary embolism severity index (PESI) scores help to anticipate adverse outcomes in the setting of APE. However, they do not utilize biomarkers and are complex to calculate during an emergency7,8. Biomarkers are valuable for risk stratification and treatment strategies in many cardiopulmonary diseases, but APE-specific markers have not been found7,9. Although troponin levels and cardiac N-terminal pro–B-type natriuretic peptide (NT-proBNP) help predict APE severity and RVD4,10, new, easily accessible, and inexpensive biomarkers will complement these markers.

Emerging evidence underscores inflammation’s pivotal role in influencing the severity of APE, leading to extensive research on the association between inflammatory markers and APE severity11-13. Predicting RVD through inflammatory biomarkers may help improve risk stratification, prioritize cardiac evaluation, and identify APE patients with high mortality risk. For this purpose, straightforward parameters that can be promptly analyzed have been sought in recent years14.

In recent studies, immature granulocytes (IGs) have been investigated as a marker of inflammation, usually for coronavirus disease 2019 (COVID-19), sepsis, and pancreatitis15-17. In this study, we aimed to investigate the usefulness of the IG count in whole blood as an inflammatory biomarker in predicting RVD in APE patients.

Methods

Study Design

We conducted a single-center, retrospective cohort study between January 2019 and June 2022, evaluating patients admitted to the emergency department of Medipol University Hospital with APE diagnosis. We assessed the relationship between IG count in whole blood and RVD on echocardiography (ECHO)  in patients diagnosed with APE. Data, including case characteristics, laboratory tests, computed tomography (CT) pulmonary angiography (CTPA), and ECHO evaluations, were obtained from the hospital’s electronic database.

In the study, we included patients aged over 18 years with APE diagnosed by CTPA, hemogram evaluation on admission, and post-diagnostic ECHO evaluation. We excluded patients with a disease affecting bone marrow neutrophil production. More specifically, the exclusion criteria were hematologic disease, autoimmune disease, immunosuppressive drug use, active cancer, deep vein thrombosis, previous pulmonary embolism, congenital heart disease, history of pulmonary hypertension, infection, or sepsis. The present study was approved by Medipol University ethical decision number 468 (E-10840098-772.02-3115).

CT

We performed pulmonary angiography using a 256-slice multidetector CT (Brilliance iCT, Philips Healthcare, Best, The Netherlands) utilizing a standard CTPA protocol according to the European Society of Cardiology guidelines4. Reports were read double-blinded by two experienced radiologists specializing in chest imaging. Consensus was sought when there was a difference in interpretation.

ECHO

All patients underwent transthoracic ECHO (TTE) examination within 24 hours after APE diagnosis, performed by the same cardiologist with more than three years of experience. We performed TTE operating an IE Elite ultrasound machine (Philips) with an S 5-1 transducer with 1-5 MHz frequency conversion. We define right ventricular dysfunction as decreased tricuspid annular plane systolic excursion measured with M-Mode (<16 mm), enlarged right ventricle, decreased peak systolic (S’) velocity of tricuspid annulus (9.5 cm/s), a right ventricle to left ventricle diameter ratio >1, and a flattened intraventricular septum4. Cases with any of the mentioned criteria are considered RVD+ group.

Hematology

Blood samples were collected during emergency department presentation within 24 hours preceding APE diagnosis. We utilized an automated hematology analyzer (XN-1000, SYSMEX, Osaka, Japan) to measure the IG count.

Statistical analysis

We calculated the continuous variables’ distribution using the Kolmogorov-Simirnov test. We present the normally distributed continuous variables as mean ± standard deviation, the non-normally distributed continuous variables as median and range (minimal-maximal values), and categorical data as frequency and percentage. We used ANOVA and independent sample t-tests to analyze and compare normally distributed variables between groups. In contrast, we used the Kruskal-Wallis and Mann-Whitney U tests to analyze non-normally distributed independent variables and the chi-square test to analyze qualitative independent variables. The receiver operating characteristic (ROC) curve investigated the effect level and cut-off value. We analyzed the effect level using univariate and multivariate logistic regression, and a p-value less than 0.05 was considered statistically significant for all analyses. We performed statistical analysis in the present study with the IBM SPSS Statistics for Windows, Version 28.0. (IBM Corp., Armonk, NY, USA).

Results

Table 1 presents the basic characteristics and laboratory data of the study population. Nineteen of the 59 patients (32 %) had RVD, and 40 (68 %) did not have RVD. There was no significant difference between patients with and without RVD regarding age and gender distribution or the presence of comorbid diseases (Table 1). The IG count was significantly higher in patients with RVD than those without RVD (p =0.001). Figure 1 illustrates the mean IG counts of patients with and without RVD.

Figure 1: Boxplot showing the mean values of immature granulocyte counts according to the presence of right ventricular dysfunction. The mean immature granulocyte count was significantly higher in patients with right ventricular dysfunction (p =0.001).
IG: immature granulocyte, RVD: right ventricular dysfunction.

Table 2 displays the results of univariate and multivariate logistic regression analyses. In the univariate model, we observed significant efficiency of the IG count in differentiating the subjects with and without RVD (p =0.004). Other variables were not effective. In the multivariate model, we observed significant and independent efficacy of the IG count in separating the cases with and without RVD (p =0.006).

Figure 2 displays the ROC curve analysis performed to predict RVD in APE. We observed a significant efficiency [area under the curve: 0.737 (0.605-0.869)] of the IG count. Significant efficacy [area under the curve 0.695 (0.553–0.837)] for an IG cut-off value of 0.05 was observed to discriminate between cases with and without RVD (p =0.016). The sensitivity, positive predictive value, specificity, and negative predictive value were 78.9 %, 48.4 %, 60.0 %, and 85.7 %, respectively, for an IG cut-off value of 0.05 (Table 3).

Figure 2: Receiver operating characteristic curve analysis showing the area under the curve for immature granulocyte count (dotted line) and for immature granulocyte count cutoff value of 0.05 to predict right ventricular dysfunction in acute pulmonary embolism patients.

Discussion

Our study demonstrated that an IG (103/uL) cut-off value of 0.05 was a significant and independent predictor of RVD in cases admitted to the emergency department with APE diagnosis. Although this finding has not been investigated in the literature, a high IG count may be an unexplored, valuable prognostic marker for assessing pulmonary embolism severity independent of hemodynamic instability.

RVD is the leading cause of poor prognosis in patients with APE. Therefore, prompt and accurate determination of RVD is an important prerequisite3. Inflammation plays an important role in APE and in the development of RVD in APE patients18. Despite the beneficial effects of delayed neutrophil activation on thrombus resolution, neutrophils are significantly implicated in the pathogenesis of acute right ventricular injury during the early inflammatory phase following APE5,18,19. Watts et al also demonstrated the central role of neutrophils and macrophages in developing right ventricular injury and remodeling after APE20.

In autoimmune diseases, cancer, and severe events such as sepsis, trauma, viral infections, and systemic inflammation can trigger immediate granulopoiesis by increasing the release of immature neutrophils into the blood and neutrophil production21. Polymorphonuclear neutrophil granulocytes, induced by granulocyte-colony stimulating factor, develop from progenitor cells and mature into mature segmented neutrophils in several stages in the bone marrow22,23. They pass into the peripheral blood after 7-10 days of maturation. In healthy individuals, these neutrophil precursors, i.e., IGs, are not present in the peripheral blood. Therefore, high levels and frequencies of IGs in peripheral blood reflect bone marrow activation22.

An elevation in circulating IGs may occur as a compensatory response to the sharp decline in activated neutrophil levels24.The half-life of IGs is three hours, which easily reflects the state of inflammation compared with other parameters with longer half-lives16,25. They are also obtained quickly, easily, and inexpensively as part of a complete blood count measurement26.

IGs have been previously investigated as a prognostic parameter in different inflammatory conditions. Daix et al showed that an increased postoperative IG count was associated with postoperative organ failure27. Nahm et al found that IGs may be valuable in evaluating the severity of sepsis and prognosis in patients with suspected sepsis25. Combadière et al associated the increase in the percentage of circulating IGs with the severity of the disease and thromboembolic complications in COVID-19 cases28.

Considering the importance of neutrophils in APE and APE-related RVD injury18,20, the number of circulating IGs may increase after activated neutrophils rapidly decrease. Therefore, it may help predict RVD and disease severity in patients with APE.

However, to our knowledge, only one study has investigated the association of IGs with APE prognosis. Kong et al found that IG elevation was a significant and independent predictor of mortality in APE5. However, this study did not address the relationship between the IG level and the right ventricle. In evaluating IGs as biomarkers in APE, the relationship with RVD may be guiding. In our study, we focused on the relationship between IG and RVD. We found a significant and independent relationship between RVD and an elevated IG count in APE.

Based on this new finding, an elevated IG count in APE may predict RVD and reflect mortality. In addition, our findings suggest that the high sensitivity and negative predictive values also guide differentiating patients without RVD in APE and patients with priority for evaluation. Considering the literature and our findings, IG is a new biological parameter that should be further investigated in the evaluation of disease severity independent of hemodynamic instability in patients with APE.

Our study has several limitations: the single-center and retrospective study design, the limited number of patients, and the lack of long-term follow-up limit our results. Long-term clinical outcomes and mortality need to be assessed in future research. Another limitation is the lack of comparison with other parameters reflecting RVD, such as NT-proBNP and troponin, and the lack of PESI data. Finally, although the effects of systemic inflammation have been previously investigated, we could not compare immature granulocytes with other inflammatory markers (such as proinflammatory cytokines). Large, multicenter, prospective studies are needed to confirm the clinical usefulness of IGs as a prognostic marker in patients with APE.

Conclusion

In conclusion, in our study, a high IG count was associated with RVD in APE and was a significant and independent biomarker for predicting RVD in APE. Given the easy availability and cost of IGs and our findings, IGs may serve as a novel and valuable marker for risk stratification and prognosis prediction in patients with APE.

Conflict of interest

The authors declare no competing interests.

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