Hematological Markers in Children and Adults with Atopic Dermatitis: A Retrospective Cohort Study

<b><i>Introduction:</i></b> Atopic dermatitis (AD) is a common chronic skin disease with an inflammatory pathophysiology that includes the activation of the innate and adaptive immune systems. We aimed to investigate the neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), eosinophil-to-lymphocyte ratio (ELR), and eosinophil-to-neutrophil ratio (ENR) in AD patients, according to age and disease severity. <b><i>Methods:</i></b> This is a retrospective, population-based cohort study conducted between the years 2005 and 2020, comparing hematological markers of AD patients and sex-age-ethnicity-matched controls. AD patients were further divided by age and disease severity (mild, moderate-to-severe AD). We created a decision tree to predict moderate-severe AD. <b><i>Results:</i></b> A total of 13,928 patients with AD were included in this study: 6,828 adults and 7,100 children, with 13,548 controls. NLR, PLR, and ELR were lower in children compared to adults (<i>p</i> values &lt;0.001). NLR, PLR, ELR, and ENR were increased in moderate-severe AD patients compared to mild AD patients (<i>p</i> values &lt;0.001). PLR, ELR, and ENR were increased in AD patients versus controls (<i>p</i> values &lt;0.001), with an additional increase in the NLR of moderate-to-severe AD patients. Patients with an ELR &lt;0.21, a PLR &gt;161, and ENR ≤0.016 should be considered high risk for developing severe AD, as well as patients with an ELR &gt;0.21 and age at diagnosis &lt;30 or age &gt;30 years and mean platelet volume ≤9. <b><i>Conclusion:</i></b> Hematological ratios were significantly higher in moderate-to-severe AD patients, compared to mild AD patients. Hematological markers were lower in children with AD compared to adults, except for ENR, likely reflecting age-related changes in blood count parameters. These markers can assist in the management and follow-up of AD patients.