Comparison of Niacin Skin Flush Response in Patients with Schizophrenia and Bipolar Disorder

Background: Patients with schizophrenia have abnormal skin flush response to niacin. We aimed to evaluate the accuracy of niacin skin test in these patients. Objectives: We aimed to evaluate the accuracy of niacin skin test in these patients. Materials and Methods: This diagnostic trial with parallel-group design was conducted at the Noor university hospital in Isfahan (Iran) from January to September 2014. Participated Subjects were hospitalized schizophrenic adult and their first degree relatives, bipolar disorder patients and healthy controls (n = 25 in each group). Niacin skin test was performed using 0.5 mL of 0.1M and 0.01M diluted methyl nicotinate solutions applied every 5 minutes for a total of 20 minutes and graded from 0 (no redness) to 3 (extreme redness). Sensitivity, specificity, and positive and negative predictive values were calculated. Results: The time point at which there was no further significant change in the skin response was 10 minutes after the test. At this set point, schizophrenic patients had lower response to each solutions compared to others (P < 0.001), but there was no difference between bipolar disorder patients and controls (P > 0.05). A grade of <= 1 skin response to the 0.01 M solution of methyl nicotinate would provide sensitivity, specificity, positive and negative predictive values of 80%, 93.3%, 80%, and 93.3%, respectively, in differentiating schizophrenic from other groups. Using 0.1 M solution provide lower sensitivity (32%) and negative predictive value (81.5%), but higher specificity (100%) and positive predictive value (100%). Conclusions: Niacin skin flush response is impaired in schizophrenic patients. This phenomenon may be used as a complementary diagnostic test in psychiatric workups.