The purpose of our study was to investigate the differences in niacin skin flush responses between schizophrenic patients and normal controls, using visual rating methods and laser Doppler flowmetry, and identifying the possible confounding effect of age, smoking and medication.

107 patients who met the DSM-IV criteria for schizophrenia and 81 healthy controls with no history of major psychiatric disorder participated. All subjects met certain inclusion criteria and written informed consent was obtained. Niacin skin test was performed administering four different solutions of aqueous ethyl nicotinate (0.1M, 0.01M, 0.001M, 0.0001M) for one minute on the forearm skin. Reaction was rated visually after 5, 10 and 15 minutes using a 4-point rating scale, considering the local appearance of erythema and oedema. When using laser Doppler flowmetry, mean blood flow change in capillary vessels was measured in perfusion units (PU), in 15 minutes time.

We performed Kruskal-Wallis test to analyze differences in skin flush response. In the schizophrenic group, flush response- rated by the visual method and compared to controls- was significantly lower at every concentration used (p<0,0001) and decreasing with age. In 58 % of the schizophrenic subjects- while only in 28 % of the controls- less then 30 PU in blood flow change could be measured by laser Doppler flowmetry.

Both methods revealed the most remarkable distinction at 0,001M concentration. There were no significant differences considering age and gender and we found no significant effect of smoking and type of antipsychotic medication, when comparing particular subgroups of schizophrenic patients.