Lymphocytes have a significant positive correlation with ADHD symptoms severity, namely, total Conner’s scale and inattention (p = 0.021 and 0.004 respectively), while NLR has a significant negative correlation with total Conner’s score and impulsivity (p = 0.046, p = 0.038), also a negative correlation yet not significant between serum Claudin-5 level and total Conner’s score, hyperactivity, impulsivity, and inattention. Here, CLDN5 is linked to attention deficit-hyperactivity disorder.