Birkenhäger TK, Geldermans S, Van den Broek WW, van Beveren N, Fekkes D.
J Psychiatr Res. 2012 Jan 11. [Epub ahead of print]

Abstract
BACKGROUND: Since there are few data on the possible association between BDNF levels and characteristics of major depression, the present study assesses brain-derived neurotrophic factor (BDNF) levels in three drug-free patient samples, and explores whether episode duration, and severity correlate with serum BDNF levels.
METHOD: Serum BDNF levels were measured in 42 drug-free patients with major depression. The duration of the index episode and the presence of psychotic features were assessed with the Schedule for Affective Disorders and Schizophrenia, and the severity of depression was measured with the 17-item Hamilton Rating Scale for Depression. The sample was divided into three groups: severely depressed inpatients without psychotic features, severely depressed inpatients with psychotic features, and moderately depressed outpatients.
RESULTS: Mean serum BDNF level in the total sample was 18.0 ± 2.8 ng/ml, with no significant difference between the three patient samples (F = 1.80, df = 2, p = 0.18). Mean serum BDNF level was significantly lower in patients with an index episode over one year, compared with patients who had a shorter index episode (F = 4.90, df = 1, p = 0.033).
CONCLUSION: These data show that patients with a long index episode have significantly lower serum BDNF levels. We found no influence of the presence of psychotic features and severity of depression on serum BDNF levels.