BACKGROUND Atopic dermatitis (AD) is an inflammatory disease with diverse clinical features. Although AD is diagnosed mainly by clinical features, the laboratory abnormalities can be found in most patients and may be of diagnostic value. However, few studies have been performed on the clinical significance of laboratory abnormalities in adult and adolescent AD. METHODS Adult and adolescent patients with AD were included in this study. The questionnaire and dermatological examination were completed by investigators. Laboratory tests included complete blood count, serum total IgE, and allergen-specific IgE. RESULTS A total of 473 patients were recruited and 396 of them were diagnosed as AD. Increased serum total IgE level, peripheral eosinophils, and basophils were seen more frequently in AD patients than in non-AD patients (P < .05). Positive aeroallergens were seen more in AD patients than in non-AD patients (P < .05). Both total serum IgE level (R = .286, P < .001) and peripheral eosinophils (R = .444, P < .001) significantly correlated with EASI score. Serum total IgE level and extrinsic type AD decreased with age. Patients with elevated serum total IgE are more likely to have a personal history of atopic diseases (P = .014). AD-associated symptoms (such as flexural dermatitis, white dermographism, and anterior neck folds) are more frequently observed in AD patients with high serum IgE or eosinophilia (P < .05). CONCLUSIONS The serum total IgE level, allergen-specific IgE, peripheral eosinophils, and basophils are important for the diagnosis of AD. And they are associated with the severity, age groups, and clinical manifestations.