Test–retest stability of the oral niacin test and electrodermal activity in patients with schizophrenia

In schizophrenia, well-replicated findings support an attenuated niacin skin-flush response. We have previously reported a delayed skin-flush after niacin ingestion and also an association between niacin non-responding and electrodermal non-responding in schizophrenia. The stability of the niacin and electrodermal tests was now studied in a test–retest design. An additional aim was to assess the association previously found.Twenty-three patients with schizophrenia underwent two sessions 3 months apart during which an oral niacin test was conducted and electrodermal activity was measured. Despite similar values for niacin outcome variables at the group level, there was high intraindividual variation. Test–retest stability for the oral niacin test was thus low, although a trend toward correlation for the dichotomous response criterion was found. Most electrodermal measures correlated between baseline and retest. A significant association between the tests was again found; niacin non-responding implied electrodermal non-responding, providing further support for a common underlying aberration in schizophrenia.