Evaluation of Plasma Fibrinogen and D-Dimer Levels among Patients with Sickle Cell Anemia in Khartoum State, Sudan

Background: Sickle cell anemia (SCA) is an inherited hemoglobin disorder characterized by chronic hemolysis, recurrent vaso-occlusive crises, and a hypercoagulable state. Alterations in coagulation biomarkers, including fibrinogen and D-dimer, may contribute to disease complications and thrombotic risk. This study aimed to evaluate plasma fibrinogen and D-dimer levels among patients with sickle cell anemia in Khartoum State, Sudan. 

Methods: A hospital-based case-control study was conducted between October 2022 and April 2023 at the Sickle Cell Clinic of Gaffer Ibn Auf Children's Specialized Hospital, Khartoum State, Sudan. Sixty participants were enrolled, including 40 patients with sickle cell anemia and 20 apparently healthy controls. Venous blood samples were collected into trisodium citrate tubes, and platelet-poor plasma was prepared for coagulation analysis. Plasma fibrinogen was measured using a Spectrum coagulometer, while D-dimer levels were determined using the Finecare™ fluorescence immunoassay analyzer. Data were analyzed using SPSS version 18, and a p-value <0.05 was considered statistically significant. 

Results: The mean plasma fibrinogen level was 226.78 mg/dL among patients with sickle cell anemia and 242.50 mg/dL among healthy controls, with no statistically significant difference (p = 0.276). In contrast, the mean D-dimer level was significantly higher in patients than in controls (0.9953 vs. 0.2585 mg/L, p = 0.030). No statistically significant differences in fibrinogen (p = 0.429) or D-dimer levels (p = 0.077) were observed between patients with HbSS and HbAS phenotypes. 

Conclusion: Patients with sickle cell anemia demonstrated significantly elevated plasma D-dimer levels compared with healthy individuals, supporting the presence of increased coagulation activation in SCA. Plasma fibrinogen levels did not differ significantly between patients and controls. Measurement of D-dimer may serve as a useful biomarker for assessing hypercoagulability in patients with sickle cell anemia.

Sickle cell anemia (SCA) is one of the most common inherited hemoglobin disorders worldwide. It results from the inheritance of a mutant β-globin gene leading to the production of abnormal hemoglobin S (HbS). The first report of the HbS gene in Sudan was documented in 1950. Subsequent studies demonstrated that the frequency of the sickle cell gene varies considerably between different geographical regions and ethnic groups within Sudan. In Khartoum State, sickle cell disease (SCD) represents one of the major hemoglobinopathies due to the diverse ethnic composition of the population. The highest prevalence has been reported among western Sudanese ethnic groups, particularly the Messeryia tribes in Darfur and Kordofan regions. In the Blue Nile region, the prevalence ranges from 0–5% among indigenous populations and reaches approximately 16% among some migrant tribes originating from western Sudan and West Africa. Although the distribution of the sickle cell gene in northern Sudan remains incompletely characterized, available evidence suggests a lower frequency of SCD in these areas. In contrast, the presence of HbS is well established among populations of Kordofan and Darfur, particularly among the Albaggara tribes, which represent an Afro-Arab population with predominantly African ancestry [1]. Sickle cell disease is an autosomal recessive genetic disorder characterized by the production of abnormal hemoglobin that causes structural and functional abnormalities in red blood cells (RBCs). The disease involves complex pathological mechanisms, including chronic hemolysis, inflammation, endothelial dysfunction, and vaso-occlusion. Although RBC abnormalities represent the primary cause of disease manifestations, leukocytes and platelets also contribute significantly to vascular obstruction and inflammatory responses associated with vaso-occlusive crises (VOCs). Hematological parameters obtained from complete blood count (CBC) analysis may provide valuable information for assessing disease severity. Previous studies have demonstrated that increased leukocyte and platelet counts, along with decreased hemoglobin concentration and RBC indices, are associated with increased frequency of VOCs and disease complications among patients with homozygous SCD [2].  At the molecular level, SCD is caused by a single nucleotide substitution in the β-globin gene, resulting in the replacement of glutamic acid with valine at position six of the β-globin chain. Although this mutation provides a protective advantage against malaria infection, homozygous inheritance of HbS results in SCA, which is characterized by chronic anemia, recurrent painful VOCs, and progressive organ damage. Under deoxygenated conditions, HbS molecules polymerize, causing RBC deformation, membrane damage, reduced cellular flexibility, increased hemolysis, inflammation, and microvascular obstruction [3]. Sickle cell disease is associated with multiple systemic complications affecting almost every organ system. Among these complications, thrombotic events and coagulation abnormalities are increasingly recognized as important contributors to disease morbidity. Children and adults with SCD demonstrate evidence of increased thrombin generation and enhanced fibrinolytic activity, indicating continuous activation of the coagulation system even during the steady state [4]. The clinical severity of SCD is influenced by various intracellular and extracellular factors and is characterized by periods of relative clinical stability interrupted by acute vaso-occlusive and hemolytic crises [5,6]. Patients with SCD exhibit a chronic hypercoagulable state characterized by increased platelet activation, elevated markers of thrombin generation, reduced natural anticoagulant proteins, abnormal fibrinolytic activity, and increased tissue factor expression. These abnormalities may occur even in the absence of acute vaso-occlusive crises. The activation of coagulation in SCD is considered multifactorial and involves interactions between inflammation, ischemia-reperfusion injury, hemolysis, nitric oxide depletion, and increased exposure of phosphatidylserine on sickled RBC membranes [7]. D-dimer and fibrinogen are important biomarkers reflecting activation of coagulation and fibrinolysis. Elevated D-dimer levels indicate increased fibrin formation and degradation, whereas fibrinogen represents a key acute-phase protein involved in coagulation and inflammation. Assessment of these markers may provide insight into the coagulation status and thrombotic risk among individuals with SCD. Therefore, this study aimed to evaluate plasma fibrinogen and D-dimer levels among patients with sickle cell anemia compared with healthy controls in Khartoum State, Sudan.

Study design and study population

A hospital-based case-control study was conducted from October 2022 to April 2023 at the Sickle Cell Clinic of Gaffer Ibn Auf Children Specialized Hospital, Khartoum State, Sudan.

A total of 60 participants were enrolled in the study. The study population included 40 patients diagnosed with sickle cell anemia (SCA) as the case group and 20 apparently healthy individuals as the control group. Participants were matched according to age and sex distribution. Patients with confirmed SCA diagnosis were included, while individuals with other hematological disorders or acute infections were excluded.

Blood sample collection and laboratory analysis

Approximately 2 mL of venous blood was collected from each participant under aseptic conditions into tri-sodium citrate anticoagulant tubes. Platelet-poor plasma was prepared by centrifugation and used for the estimation of coagulation biomarkers.

Plasma fibrinogen concentration was measured using a coagulometer with Spectrum diagnostic reagents. Plasma D-dimer levels were determined using Finecare™ quantitative immunofluorescence assay according to the manufacturer’s instructions.

Data collection and statistical analysis

Demographic and clinical information were collected using a structured questionnaire through direct interviews with participants and review of medical records. Data were analyzed using Statistical Package for Social Sciences (SPSS), version 18. Descriptive statistics were expressed as frequencies, percentages, and means. An independent t-test was used for comparison between groups, and a p-value <0.05 was considered statistically significant.

A total of 60 participants were enrolled in this study, including 40 patients with sickle cell anemia (SCA) as the case group and 20 apparently healthy individuals as the control group. The demographic characteristics of the study participants are presented in Table 1. Among the SCA patients, 10 (25.0%) were below 10 years of age, 19 (47.5%) were aged between 10 and 19 years, and 11 (27.5%) were above 19 years. In the control group, 4 (20.0%), 10 (50.0%), and 6 (30.0%) participants belonged to the same age categories, respectively. Regarding gender distribution, males represented the majority of the SCA patients (28, 70.0%), whereas females accounted for 12 (30.0%). In the control group, males and females were equally distributed (50.0

Sickle cell anemia is associated with chronic activation of coagulation pathways and a persistent hypercoagulable state resulting from interactions between hemolysis, inflammation, endothelial dysfunction, and abnormal blood cell activation. This study evaluated plasma fibrinogen and D-dimer levels among patients with SCA compared with healthy individuals in Khartoum State, Sudan. In the present study, no statistically significant difference was observed in plasma fibrinogen levels between SCA patients and controls (p = 0.276). The mean fibrinogen concentration was slightly lower among patients with SCA compared with controls. This finding is consistent with a previous study conducted in Nigeria involving 90 participants, including patients with homozygous SCA (HbSS), individuals with sickle cell trait, and healthy controls. That study reported no significant difference in plasma fibrinogen levels between HbSS patients and healthy individuals and found no association between fibrinogen concentration and disease severity [10]. However, the current finding differs from a study conducted by Tatkare et al. in India, which included 321 patients with HbSS and 321 healthy controls. Their results demonstrated significantly elevated fibrinogen levels among patients with sickle cell anemia compared with controls [11]. The discrepancy between studies may be explained by differences in study populations, disease severity, inflammatory status, nutritional factors, and laboratory methodologies. In contrast, this study demonstrated a statistically significant elevation of plasma D-dimer levels among SCA patients compared with controls (p=0.030). Increased D-dimer concentration reflects enhanced fibrin formation and degradation, indicating continuous activation of coagulation and fibrinolytic pathways in patients with SCD. This finding supports previous evidence that patients with SCD remain in a prothrombotic state even during the steady state. The present result agrees with a study conducted by Fakunle et al. in Nigeria, which included 38 patients with homozygous sickle cell anemia and 78 healthy controls. The study reported significantly higher D-dimer levels among patients with SCA compared with controls (p = 0.001) [9]. Similarly, Amin et al. investigated African-American participants categorized into three groups: healthy controls (HbAA), sickle cell disease patients (HbSS), and sickle cell trait individuals (HbAS). They observed significantly increased D-dimer levels among both HbSS and HbAS groups compared with HbAA controls (p = 0.001 and p = 0.017, respectively) [8]. Furthermore, the current findings are consistent with a Sudanese study conducted by Mahdi et al. among children with SCA during steady state, which demonstrated significantly higher D-dimer levels in SCA patients compared with healthy controls (p < 0.001) [12]. These findings confirm the role of D-dimer as a useful marker of coagulation activation in patients with sickle cell anemia. When coagulation markers were analyzed according to hemoglobin genotype, patients with HbSS demonstrated higher D-dimer levels compared with HbAS patients; however, the difference was not statistically significant (p = 0.077). Similarly, fibrinogen levels did not differ significantly between HbSS and HbAS groups (p = 0.429). The absence of statistical significance may be attributed to the relatively small number of participants, particularly in the HbAS subgroup.

This study had some limitations that should be considered when interpreting the findings. First, the relatively small sample size and the inclusion of participants from a single healthcare facility may limit the generalizability of the results to all patients with sickle cell anemia in Sudan. Second, the cross-sectional case-control design provides information about coagulation status at a specific time point but does not allow assessment of changes in coagulation biomarkers over time or their relationship with disease progression and clinical outcomes. Third, clinical parameters such as frequency of vaso-occlusive crises, history of thrombotic events, inflammatory markers, and disease severity indicators were not fully evaluated, which may have provided additional insight into the association between coagulation activation and clinical manifestations. Finally, the number of participants with different hemoglobin phenotypes, particularly HbAS, was limited; therefore, further studies with larger sample sizes are needed to confirm the observed differences between genotypes.

This study demonstrated that patients with sickle cell anemia had significantly elevated plasma D-dimer levels compared with healthy controls, suggesting increased activation of coagulation and fibrinolysis among SCA patients. However, plasma fibrinogen levels did not show a significant difference between patients and controls. Assessment of coagulation biomarkers, particularly D-dimer, may provide valuable information regarding thrombotic risk and disease-related coagulation abnormalities in individuals with sickle cell anemia.

Recommendations

Further multicenter studies with larger sample sizes are recommended to provide a more comprehensive understanding of coagulation abnormalities among patients with sickle cell disease in Sudan. Longitudinal investigations are also needed to evaluate changes in coagulation biomarkers during steady-state conditions and vaso-occlusive crises and to determine their association with disease severity and thrombotic complications. Routine assessment of coagulation markers, particularly D-dimer, may be considered as part of the clinical evaluation of patients with sickle cell disease to identify individuals at increased risk of thrombotic events. Future studies should also include additional clinical and laboratory parameters, such as inflammatory markers, platelet activation indicators, endothelial dysfunction markers, and hematological indices, to better characterize the mechanisms contributing to the hypercoagulable state associated with sickle cell disease.

Consent
The patient’s written consent has been collected 

Ethical Approval

Ethical approval for this study was obtained from the relevant institutional ethical review committee before the commencement of the research. The study was conducted in accordance with the principles of the Declaration of Helsinki. Written informed consent was obtained from all participants or their legal guardians before sample collection and participation in the study. All collected data were kept confidential and used exclusively for research purposes.

Competing Interests

Authors have declared that no competing interests exist.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.