Analysis of neutrophil to lymphocyte ratio, platelet to lymphocyte ratio and mean platelet volume to platelet count ratio in children with acute stage of immunoglobulin A vasculitis and assessment of their suitability for predicting the course of the disease

In searching for parameters useful for predicting the course of IgAV (risk of systemic involvement) and making decisions about treatment, it is important to know the complex mechanisms responsible for migration and infiltration of neutrophils into the perivascular space, which ultimately contributes to the development of inflammation with their dominant participation [19]. As the ratio of particular types of white blood cells, rather than their total number, is considered to have a higher prognostic value in assessing the severity of inflammation, in our study, we assessed the ratio of neutrophils to lymphocytes as well as PLR and MPR ratios.

The significantly higher neutrophil counts and the value of the NLR in children with IgAV documented in our study confirm their participation in the pathogenesis of the disease. It is known that neutrophils are not only the first effector cells flowing into the site of injury/inflammation removing extracellular pathogens but they also affect the activation, regulation, and function of other cells of the immune system, among others, through the release of cytokines, extracellular traps, and effector molecules [20]. The current research shows that the NLR, showing changes in particular populations in the total leukocyte pool, is associated with higher severity of inflammation and, thus, with a more severe course of the disease [13, 21]. This is confirmed by the results of our research because NLR, like the neutrophils count, was higher in children with the severe course of the disease and/or systemic involvement. Moreover, ROC curve analysis showed that NLR is the best predictor of systemic involvement in children with IgAV with an optimal cutoff value of 2.73 (sensitivity 53.7%, specificity 90%). Previous research by Makay et al. and Hee Hong et al. which showed significantly higher NLR values in the group of patients with GT bleeding coincide with ours (cutoff value 2.82, 81% sensitivity, 76% specificity and cutoff value 2, 86, sensitivity 73%, specificity 68% respectively) [13, 22]. In our study, we also showed elevated PLT and PLR in the group of children with systemic involvement (cutoff value 124.04, sensitivity 65.9%, specificity 73.3%). Similarly, Gayret et al. showed that PLT and PLR are significantly higher in children with GT bleeding but in contrast to the studies of other authors and ours he did not confirm the increase of neutrophils and NLR in this group of patients [14].

Reactive thrombocytosis can be observed in various clinical conditions (acute or chronic infection, trauma, malignancy). The aforementioned cellular shifts associated with the immune response to the ongoing non-specific inflammatory process (neutrophilia, lymphopenia) influence changes in the values of both PLR and NLR. Significantly increased levels of cytokines in the acute phase of IgAV, including TNF-alpha, IL-6, IL-8, are responsible for thrombocytosis, elevated CRP, more severe course of the disease, and a higher risk of renal involvement [23‐26]. Three main elements are considered to be a measure of platelet activation: MPV (which determines the average size of platelets and reflects their production in the bone marrow), PDW (index of inhomogeneity of the size of the platelets) and the number of platelets [27]. The healthy population shows an inverse relationship between MPV and platelet count [28]. Reactive thrombocytosis is often accompanied by low MPV and PDW [29]. Activated platelets play an important role in the systemic inflammatory response through the release of inflammatory mediators and the presentation of surface molecules (including P-selectin, E-selectin) that affect their interactions with other cells [30]. Larger platelets are more active, contain more mediators (serotonin, adenosine diphosphate, platelet-derived growth factor, β-thromboglobulin) and show greater expression of adhesion molecules (glycoproteins Ib, and glycoprotein IIb-IIIa) [31]. In addition, due to the presence of a ligand for P-selectin on the surface of neutrophils (PSGL-1, P-selectin glycoprotein ligand-1), the platelets can affect neutrophils and stimulate cytokine synthesis by neutrophils and their migration to surrounding tissues [32]. It has been previously shown that low MPV may correlate with GT bleeding in the course of IgAV [12, 13]. We have not demonstrated such dependencies in our work. MPV and PDW were similar in children with IgAV and did not differ from those observed in healthy children. Data on the usefulness of the MPV in other inflammatory diseases are divergent. In the acute phase of rheumatic diseases, a decrease in MPV [33, 34] or its increase associated with higher activity of juvenile idiopathic arthritis, psoriatic arthritis, SLE may occur [5, 35, 36]. Some studies indicate the usefulness of MPV in monitoring anti-inflammatory therapy in rheumatoid arthritis [37]. Conflicting research results concern vascular diseases, indicating an increase in MPV values in peripheral and coronary artery diseases [38, 39] or a lack of MPV association with coronary disease severity [40]. According to Shin DH et al., larger MPV is not associated with higher platelet reactivity, but indicates their reduced aggregation, because larger platelets may not be fully mature and appear as a result of their accelerated release from the bone marrow [31].

MPR calculated by dividing the MPV by the PLT is suggested to be the better indicator of platelet activation and, thus, the severity of the inflammatory process. The relationship between MPR and prognosis in critically ill patients, in malignancies and in febrile seizures in children [31, 41‐43] has been studied so far. In the presented study, the MPR was significantly lower in all IgAV children and in the systemic involvement group. This indicates the usefulness of MPR to predict systemic involvement in IgAV. The ROC curve analysis showed the lowest sensitivity and specificity for this index (63.4% and 63.3%, respectively, p = 0.04), which means that it requires further research on a larger group of patients.

It is important that the interpretation of results includes physiological cellular shifts (between the circulating pool and the tissue pool) that occur during bleeding and cause neutrophilia during the first hours [44]. Other factors that may affect the tested ratios, i.e., thyroid dysfunction, diabetes, renal and hepatic failure, are less important in children than in the adult patients (they were not observed in our cohort); however, they should be kept in mind [45]. The causes of thrombocythemia include chronic iron deficiency, hyposplenism, congenital lack of spleen, status after spleen removal, alcoholism, hemolytic anemia [46, 47] and used drugs (antibiotics, corticosteroids, non-steroidal inflammatory drugs). As it is known, in children with IgAV, the incidence is higher in autumn and winter and is usually associated with the infectious factor, which was also confirmed by our research (55% of new cases in the autumn and winter season and 56% occurrence of the infectious trigger factor). Therefore, changes in leukocyte populations reflect the body’s response to an ongoing inflammatory process per se and it may be modified by the pharmacological treatment. The logistic regression analysis showed a higher risk of systemic involvement with higher values of NLR and the analysis of ROC curves showed NLR as the best predictor of organ involvement. PLR was also found to be associated with systemic involvement but with lower AUC. That is why NLR is a more valuable indicator to identify patients at higher risk for systemic involvement in the course of IgAV.

In our study group, all patients with renal involvement also presented features of GT bleeding; therefore, it was impossible to assess the above ratios in children with only renal involvement. Ozturk and Ekinci (2 patients with only renal involvement) [44] and Nagy et al. (6 patients with only renal involvement) [48] suggest that IgAV should be considered as systemic involvement or extracutaneous involvement as a determinant of a severe course of the disease. In the group we studied, we additionally applied an objective scale of disease severity, including joint, renal and GT symptoms (Table 1) [16‐18]. We did not show a significant difference in NLR, PLR and MPR between the severe and mild group. It may be result from the low number of patients in severe group (n = 12) and the fact that to the mild group were classified children with less severe systemic involvement who did not yet meet the point criterion. The limitation of the scale used is related to not including other rare manifestations of IgAV, such as acute scrotum, central nervous system disorders, myositis, myocardial involvement, which may be severe. In addition, it should be analyzed, as suggested by other authors, whether the selected cutoff point in the severity of the disease (4 points) was rightly adopted.

Additionally, it would be valuable to assess the correlation between the extent of skin lesions and the indicators: NLR, PLR, and MPR, which has not been studied so far. In our study group, such an assessment was not possible because of the similar distribution of skin lesions in all patients.

The retrospective character of single-center studies and a small study group may limit the value of statistical analyses. Another limiting factor may result from the different time from the onset of the disease symptoms to the collection of a blood sample; however, it should be noted that the first (pre-treatment) peripheral blood count was used for the analysis.

In conclusion, NLR is a more valuable indicator than PLR to identify patients at higher risk of systemic involvement in the course of IgAV. MPR was significantly lower in the systemic involvement group, which also indicates its usefulness in assessing the course of the disease. However, due to the fact that it was characterized by the lowest sensitivity and specificity, its use requires further research. Due to the multitude of factors affecting the results of peripheral blood counts, the above ratios should not be decisive in clinical doubts. As always, clinical observation and individual approach to the patient are most important. It is necessary to determine the cutoff values of the tested ratios, which will allow for selecting patients with GT symptoms who should receive early corticosteroids or isolating patients who require increased supervision (e.g., hospital observation). Further prospective and multicenter studies on the usefulness of the above-mentioned parameters for predicting the severity of the disease and seeking new ratios to facilitate clinical decision making are needed.