Attenuated and delayed niacin skin flushing in schizophrenia and affective disorders: A potential clinical auxiliary diagnostic marker.

Aim: Schizophrenia and affective disorders all show high heterogeneity in clinical manifestations. A lack of objective biomarkers has long been a challenge in the clinical diagnosis of these diseases. In this study, we aimed to investigate the performance of niacin skin flushing in schizophrenia and affective disorders and determine its clinical potential as an auxiliary diagnostic marker.

Methods: In this case-control study, niacin skin-flushing tests were conducted in 613 patients (including 307 schizophrenia patients, 179 bipolar disorder patients, and 127 unipolar depression patients) and 148 healthy controls (HCs) with a modified method. Differences in niacin skin-flushing responses were compared with adjustment for gender, BMI, age, nicotine dependence, alcohol consumption and educational status. A diagnostic model was established based on a bivariate cut-off.

Results: Schizophrenia and affective disorders showed similar performance of niacin bluntness, characterized by attenuated flushing extent and reduced flushing rate. An innovative bivariate cut-off was established according to these two features, by which we could identify -patients with either schizophrenia or affective disorders from HCs with a sensitivity of 55.28%, a specificity of 83.56% and a positive predictive value of 93.66%.

Conclusions: The niacin-induced skin flushing was prevalently blunted in patients with schizophrenia or affective disorders, indicating a promising potential as an auxiliary diagnostic marker in risk prediction and clinical management of these disorders. Additionally, the niacin-blunted subgroup implies a common biological basis in the investigated disorders, which provokes new thoughts in elucidating the pathological mechanisms.