Hematologic Profiles and Depressive Disorder in Adolescents: Evidence from a Large Electronic Health Record Study

Objective: Despite growing evidence linking inflammation to depression, relatively little is known about whether routinely measured hematologic parameters reflect depressive states in adolescents.Because low-grade inflammation may influence hematopoiesis, we examined whether peripheral blood indices obtained from routine complete blood counts are associated with depressive symptom severity among South Korean adolescents.Methods: We retrospectively analyzed electronic health record data from 1,074 adolescents with depressive disorders and 1,220 healthy controls aged 13-18 years.Depressive symptoms were assessed using the 17-item Hamilton Depression Rating Scale.Associations between hematologic parameters and depressive symptoms were examined using correlation analyses and multivariable least absolute shrinkage and selection operator regression with bootstrapping.Results: Compared with controls, adolescents with depression showed significantly lower erythrocyte-related indices, including hemoglobin, hematocrit, red blood cell count, and mean corpuscular hemoglobin concentration.Platelet and white blood cell counts were modestly elevated in the depression group, although most leukocyte-related indices were not significant after adjustment.Greater depressive symptom severity was associated with lower hemoglobin, hematocrit, red blood cell count, and eosinophil levels.In penalized regression analyses, hemoglobin demonstrated the most robust and stable association with depressive symptom severity across multiple analytical approaches.Conclusion: These findings suggest that erythrocyte-related indices, particularly hemoglobin, may reflect peripheral physiological alterations accompanying depressive states in adolescence and may provide clinically accessible indicators of inflammatory or hematopoietic processes associated with adolescent depression.