Platelet indices and neutrophil:lymphocyte ratio as a predictive tool in acute sickle cell vaso-occlusive crisis: A study protocol

Introduction

The sickle cell disease (SCD)-causing globin gene mutation can be inherited homozygously or compound heterozygously. The hydrophobic amino acid valine replaces the hydrophilic amino acid glutamic acid in the sixth position to produce haemoglobin S (HbS). HbS polymerizes as a result of deoxygenation, and this polymerization is associated with both increased red cell density and cell dehydration. The disease’s acute (painful episodes, acute chest syndrome) and chronic (avascular necrosis, renal insufficiency) consequences are considered to be caused by the thick, rigid, and sickling red cells, which cause vaso-occlusion and reduced blood flow and are associated with these symptoms.¹

In SCD, the complicated interactions between sickled erythrocytes, endothelial cells, leukocytes, platelets, and plasma proteins lead to the vaso-occlusive crisis (VOC). It is generally known that platelets play a part in these interactions. While platelet levels typically rise and are functionally hyperactive in the “steady-state” of sickle cell illness, during a sickle cell crisis, platelet count falls first and then increases, later on, during recovery. Although it is uncommon, acute splenic sequestration, aplastic crisis brought on by parvovirus B19 infection, and fat embolism can all cause thrombocytopenia.²

Vaso-occlusive crises are associated with enhanced platelet reactivity and activation, which raises platelet volume and widens platelet distribution. Moreover, patients with sickle cell anaemia who experienced more crises had higher platelet concentrations than other patients. In contrast to wealthy nations, patients in central India, also referred to as the sickle cell belt, sadly experience more severe symptoms, with vaso-occlusive crisis and stroke being the two main clinical manifestations.³ A number of studies done in this region reflect on the severity of SCD related complications.^4–6

In addition to the pain associated with VOC, there are a number of clinical consequences. Acute chest syndrome, acute bone pain, hepatic and renal involvement, cerebrovascular accident, and multi-organ failure resulting in death can develop in association with SCD which comprises of VOC. All these presentations of SCD will be included in this study.^5,6

In several inflammatory and hemolytic illnesses, mean platelet volume serves as a prognostic indicator. Moreover, higher platelet production will result in larger, more reactive platelets with a larger mean platelet size, hence the MPV readings can be utilised to draw conclusions about disorders causing platelet destruction.³

The high cost of hydroxyurea therapy for sickle cell anaemia challenges the significant population that hail from tribal and socioeconomically disadvantaged backgrounds. Also, there hasn’t been much research done on the use of platelet counts as prognostic indicators, which might be very helpful, particularly for a nation like India with a significant population of sickle cell sufferers. As a result, the goal of this study is to evaluate the role of platelet indices in the early identification of patients at a higher risk of crisis. If a positive correlation is found, platelet indices may be used as a required investigation in the evaluation of sickle cell patients to predict the possibility of vaso-occlusive crisis and to start hydroxyurea therapy early for better patient outcomes.³

Protocol

Setting

The study will be conducted in the Department of Medicine, at a tertiary care teaching hospital Acharya Vinoba Bhave Rural hospital situated in the rural area of Wardha district. The overview of the study has been shown in Figure 1.

Figure 1. Study flow chart showing the overview of the study.

Methods

The following data will be collected for all patients with SCD older than 18 years of age.

Discussion

The most often performed laboratory test in patients with sickle cell disease is the complete blood counts. Little is known, however, about the frequency of platelet-count abnormalities, clinical correlation of various forms of sickle cell crises, and the prognostic importance of platelet indices in these critically ill patients in the ICU. This is the main reason behind designing this protocol.³

Common complications include vaso-occlusive crisis and stroke. The main event in pathophysiology of sickle cell crisis is vaso-occlusion with ischemia-reperfusion damage, although the pathophysiology at play is complicated.³ Deoxyhemoglobin S polymerization causes tissue ischemia, which causes both acute and chronic pain. It can also cause damage to any organ in the body including the bones, joints, brain, eyes, liver, kidneys and lungs. SCD activates all cellular components in the blood system.⁴

Additionally, aberrant red cells and activated platelets may interact, resulting in vaso-occlusion and aggregation. MPV is a simple way to measure platelet activation and function.^3,7

In illnesses like idiopathic thrombocytopenic purpura, platelet production and/or destruction are accelerated and MPV, a measure of platelet size, is increased. In individuals with coronary heart disease, higher MPV levels have been found to be an independent risk factor for myocardial infarction, as well as for death or recurrent vascular events following myocardial infarction.⁴

Studies have linked high NLR with clinical outcomes in cardiovascular disease, malignancies, as well as renal disease in SCD NLR has been proposed as marker of inflammation. The transition from steady state to vaso- occlusive crisis (VOC) is facilitated by leukocytes, which are both elevated and active in SCD. By secreting pro-inflammatory mediators and expressing related adhesion molecules, leukocytes increase the adhesiveness of the endothelial cells in the presence of the proper VOC-producing substances, hence intensifying vaso-occlusion and the pain process.⁵

Just prior to or during VOC, there is a surge in hematopoietic activity in addition to the shift of the marginating leukocytes to the circulation pool. The significant leukocytosis seen in the VOC group as opposed to the steady state non vaso occlusive SCD patients may be caused by this. The tendency of leukocytes to stick to the postcapillary venular endothelium is increased during leukocytosis, which reduces the vessel lumen. Sickled and unsickled RBCs, platelets and leukocytes all have a greater propensity to cling to the arterial wall and to other cells in these patients, which exacerbates this blockage. Contrarily, in these individuals, leukocytosis might be a type of defence against overwhelming infectious pathogens to which SCD patients are sensitive as a result of functional asplenia brought on by repeated splenic infarction. Patients with functional asplenia are more susceptible to severe infections, especially those caused by encapsulated pathogens such as Streptococcus pneumoniae and Hemophilus influenzae.⁸

In SCD patients, a high NLR increases the chance of developing VOC and other end-organ damage. In line with John et al., this study aims to discover the relation of NLRs in SCD patients as compared to HbA controls.⁸ Another study, on the other hand, was unable to show a connection between increased NLR and sickle cell nephropathy, perhaps as a result of the cohort being made up of SCD patients in the steady state.⁸

In line with earlier studies, a rebound thrombocytosis may have been the cause of the dramatically higher platelet count in the VOC and steady state group. Due to the compensating feedback impact that anaemia has on the synthesis of erythropoietin, rebound thrombocytosis may coexist with hemolytic anemias and the anaemia caused by chronic diseases. The structural similarity between erythropoietin and thrombopoietin is to blame for this. Additionally, hyposplenism in SCD excludes the spleen’s pooling impact on platelets, which greatly contributes to the high platelet count seen in voc state.⁸

Although there is no statistically significant difference between the steady state and VOC groups in the percentage of haemoglobin S in each red blood cell, it is inversely correlated with HbF levels and inversely proportionate to the degree of polymerization of deoxygenated sickle haemoglobin. However, in all previous studies conducted, NLR was not correlated with HbF.⁸

The neutrophil and platelet contributions to the chronic inflammatory state in SCD patients are supported by the positive connection between neutrophil to lymphocyte ratio in these individuals. These ratios may serve as reliable, inexpensive and stable indicators of inflammation. When determining the level of inflammation in SCD patients, the use of these simple indicators may be beneficial and superior to using absolute neutrophil count or platelet count alone.⁸

This is due to the fact that these ratios are a little bit more stable and are less susceptible to the physiological, pathological or stressful circumstances that are known to affect platelet and neutrophil counts.⁸