Discussion
The results of this study showed that MPV, which can be rapidly and safely measured, has significant predictive value for the diagnosis of COVID-19. In addition, regardless of the threshold values, MPV was seen to have better predictive capacity than lymphocyte values.
In reports from several countries, it has been stated that children infected with COVID-19 are mild, or more often asymptomatic carriers, and thus play a major role in the spread of the disease. By spreading the disease, delayed diagnosis of asymptomatic children may be a reason for increased morbidity and mortality (10). Although RT-PCR or genetic sequencing used in COVID-19 diagnosis are the gold standard, these methods are not available in all centres, and they are expensive (19, 20). Therefore, there is a need for a simpler and more practical method. Leukocyte, neutrophil, lymphocyte and platelet counts, and CRP level are simple parameters, most of which are provided by an automatic hematology analyser readily available on the market.
In a study of adult patients by Huang C et al (21), there was determined to be lymphopenia in 63% of cases, leukopenia in 25% and leukocytosis in 30%, no significant change was found in neutrophil values, and thrombocytopenia was determined to have developed in 5%. Liu et al (22) reported that the most common laboratory abnormalities in adult patients were lymphopenia and decreased lymphocyte percentage. Low lymphocyte levels were associated with the viral load of COVID-19 determined in the respiratory tract and the severity of the disease.
In the early laboratory values of a study of paediatric patients by Sehen et al (19), leukocyte count was determined to be normal or low, and an increase was determined in lymphopenia and CRP level. In a study by Chen et al (23), it was reported that CRP could be normal or high in paediatric patients. Consistent with these findings in literature, lymphocyte measurements in the current study were determined to be significantly low in COVID-19 positive patients. Although the leukocyte, neutrophil, and platelet counts were lower than those of the control group, this decrease was not determined to be statistically significant (p>0.05). No significant difference was determined between the groups in respect of the CRP levels.
MPV is a simple, inexpensive, and easily obtained biomarker of thrombocyte function, and can be measured in almost all laboratories. Thrombocyte volume shows a correlation with thrombocyte function and activation (24). In addition to primary hemostatic functions, thrombocytes play a role in the pathogenesis of infectious diseases (25). Previous studies have suggested that megakaryocyte ploidy may be affected by cytokines such as IL-3 and IL-6, and this could lead to greater and more reactive production of thrombocytes (26).
Acute hepatitis A is characterised by a low or only moderate level of acute phase reaction, especially in children with an asymptomatic course (27). Torre et al (28) reported an increase in IL-1a, IL-6, and TNF-a serum levels in the acute phase of acute hepatitis A disease. In a study of patients diagnosed with hepatitis A by Akin et al (29), an increase was determined in MPV values and it was reported that increased pro-inflammatory cytokines could contribute to the increase in MPV values. Gao et al (30) determined that IL-6 levels increased in proportion with the severity of the disease in patients diagnosed with COVID-19. High levels of IL-6 in COVID-19 may be a result of increasing MPV. Based on these observations of MPV, it can be concluded that this inflammation marker could be used for the diagnosis of COVID-19.
To the best of our knowledge, this is the first study to have investigated the relationship between MPV and COVID-19. Of the inflammatory markers examined in this study, COVID-19 was not determined to have caused any significant change in WBC, neutrophil and platelet counts or CRP level, and consistent with literature, a significant decrease was determined in lymphocyte count. When a cutoff value of ≥8.74 fl MPV was used in the prediction of COVID-19, sensitivity and specificity were 81.82% and 95.00% respectively and positive and negative predictive values were 93.75 and 85.07, respectively. A cutoff value of ≤2.12 mm3 used for lymphocytes had sensitivity of 49.09% and specificity of 86.67% in the prediction of COVID-19 with positive and negative predictive values of 77.14 and 65.00, respectively. Based on the ROC curve analysis, the sensitivity, specificity, positive and negative predictive values of MPV were higher than those of lymphocytes.