Objective <p>To investigate the possible clinical application of niacin-induced skin flush response for diagnosing psychiatric disorders in adolescents and its potential correlation with blood test -indicators.</p> Methods <p>This is a cross-sectional study that included 51 adolescents with psychiatric disorders and 18 healthy controls (control group) matched for age and gender. Demographic and clinical data and blood test results were collected. The response to niacin-induced skin flush was tested in all participants using an integrated detection platform for skin testing with niacin developed by the Chunling Wan research team at Shanghai Jiao Tong University. The differences in niacin responses between the disease and control groups were compared using the Mann–Whitney U test. The correlation between niacin responses and clinical indicators was analyzed using Spearman’s correlation analysis.</p> Results <p>Compared to the control group, the disease group exhibited lower sensitivity and weaker response intensity to niacin-induced skin flush, particularly for depression and bipolar disorder. The niacin responses showed potential as an auxiliary tool for diagnosing psychiatric disorders in adolescents. The area under the curve values of 0.891, 0.838, and 0.784 clearly distinguished between depression, bipolar disorder, and behavioral and emotional disorders, respectively. The niacin response in adolescents with psychiatric disorders was associated with thyroid hormone levels (T3, <i>p</i> = 0.030; free T3, <i>p</i> = 0.023), uric acid (<i>p</i> = 0.002) levels, red blood cell count (<i>p</i> = 0.056), and standard deviation in red blood cell distribution width (<i>p</i> = 0.023).</p> Conclusions <p>The niacin-induced skin flush response is significantly abnormal in adolescents with psychiatric disorders and can aid in clinical diagnosis. It also significantly correlates with thyroid function, antioxidant capacity, and red blood cell morphology and count.</p>