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Table 2 Study Characteristics

From: Association between BDNF levels and suicidal behaviour: a systematic review and meta-analysis

Author (year) Study design and sample groups Participants (n) Definition of suicidal behaviour Type of BDNF measurement (units) Mean (SD) BDNF levels p-value (difference between groups) Variables adjusted for
Postmortem Brain Studies
Banerjee et al. (2013) Case–control
Cases of suicide vs. non-psychiatric healthy controls
Suicide: 21
Control: 19
Completed suicide Brain – hippocampus (pg/ml) Suicide: 19.5a
Control: 44a
<0.001 None
Dwivedi et al. (2003) Case–control
Cases of suicide vs. non-psychiatric controls
Suicide: 27
Control: 21
Completed suicide Brain – PFC, hippocampus
(optical density)
PFC
Suicide + MDD: 0.94 (0.22)
Suicide + other psychiatric disorder: 0.88 (0.28)
Control: 1.61 (0.39)
Hippocampus
Suicide + MDD: 1.04 (0.20)
Suicide + other psychiatric disorder: 1.03 (0.22)
Control: 1.71 (0.44)
<0.001
<0.001
None
Karege et al. (2005) Case–control
Cases of suicide vs. non-psychiatric controls
Suicide: 30
Control: 24
Completed suicide Brain – PFC, hippocampus, entorhinal cortex
(ng/g)
Hippocampus
Drug-free MDD: 17.7 (2.9)
Drug-free others: 16.8 (3.1)
Drug-treated MDD: 23.3 (2.2)
Drug-free controls: 24.5 (3.6)
PFC
Drug-free MDD: 13.8 (2.6)
Drug-free others: 12.7 (2.6)
Drug-treated MDD: 17.9 (2.9)
Drug-free controls: 17.5 (3.0)
Entorhinal cortex Drug-free MDD: 14.1 (2.1)
Drug-free others: 13.4 (2.4)
Drug-treated MDD: 12.9 (2.3)
Drug-free controls: 13.4 (2.5)
<0.001
<0.002
Not significant
PMI, age
Maheu et al. (2013) Case–control
Depressed individuals (divided into suicide victims vs. non-suicide deaths) vs. non-psychiatric controls
Depressed suicide (12)
Depressed non-suicide (10)
Control (14)
Completed suicide Brain – BLA, CeA
(optical density)
BLA
Depressed suicide: 1.19 (0.80)
Depressed non-suicide: 1.67 (1.42)
Control: 1.08 (0.34)
CeA
Depressed suicide: 0.95 (0.20)
Depressed non-suicide: 1.87 (1.30)
Control: 0.97 (0.16)
Not significant
Not significant
PMI, brain pH, age
CSF Studies
Martinez et al. (2012) Case–control
Depressed patients vs. non-depressed patients
Depressed (18)
Non-depressed (25)
Suicidal ideation CSF
(pg/ml)
NA Correlation between BDNF concentration and SSI score: r = 0.62, P = 0.033, n = 12 None
Serum BDNF Studies
Deveci et al. (2007) Case–control
Suicide attempters vs. non-suicidal MDD patients vs. healthy controls
Suicide (10)
Non-suicidal MDD (24)
Healthy controls (26)
Suicide attempt Serum
(ng/ml)
Suicide: 21.2 (12.24)
Non-suicidal MDD: 21.2 (11.3)
Control: 31.4 (8.8)
Suicide vs. healthy controls: 0.004
Suicide vs. MDD: not significant
None
Grah et al. (2014) Case–control
MDD patients vs. PD patients vs. AD patients vs. healthy controls
Suicide (96)
Control (106) b
Suicide attempt Serum
(ng/ml)
RDD c
Suicide: 11.8 (8.88–14.73)
Control: 12.8 (10.83–14.78)
PD
Suicide: 10.7 (7.04–14.26)
Control: 15.7 (10.29–21.02)
AD
Suicide: 12.6 (9.63–15.58)
Control: 15.4 (12.04–18.77)
0.07
0.003
0.009
Age, sex, therapy
Huang & Lee (2006) Case–control
Schizophrenic patients vs. healthy controls
Suicidal schizophrenic (11)
Non-suicidal schizophrenic (115)
Healthy control (96)
Suicide attempt Serum
(ng/ml)
Suicidal schizophrenic: 14.60 (7.02)
Non-suicidal schizophrenic: 14.16 (6.94)
0.841 None
Liang et al. (2012) Case–control
Depressed patients (with or without suicide attempt) vs. healthy controls
Suicidal depressed (31)
Non-suicidal depressed (34)
Healthy control (30)
Suicide attempt, suicidal ideation Serum
(ng/ml)
Suicidal depressed: 57.3 (9.2)
Non-suicidal depressed: 76.0 (25.7)
Healthy control: 113.8 (44.4)
Suicide attempt: <0.01
Suicidal ideation: <0.01
None
Park et al. (2014) Cross-sectional
MDD patients
Suicidal MDD (18)
Non-suicidal MDD (33)
Suicide attempt Serum
(ng/ml)
Suicidal MDD: 21.93 (24.71)
Non-suicidal MDD: 24.71 (7.7)
0.3 None
Pinheiro et al. (2014) Cross-sectional
Postpartum women
History of suicide attempts (12)
No suicide history (178)
Suicide attempt, suicidal ideation Serum
(ng/ml)
Suicide: 2.11 (1.42)
Control: 2.37 (1.26)
0.6
Linear regression of PPAD and suicide risk: −0.912 (−1.73– -0.09)
p = 0.029
Previous psychiatric treatment, stressful life events during pregnancy
Plasma BDNF Studies
Kim et al. (2007) Case–control
Suicidal depressed patients vs. non-suicidal depressed patients vs. healthy controls
Suicidal depressed (32)
Non-suicidal depressed (32)
Control (30)
Suicide attempt Plasma
(pg/ml)
Suicidal depressed: 430.5 (397.0)
Non-suicidal depressed: 875.80 (663.02)
Control: 889.4 (611.3)
0.002 None
Lee et al. (2007) Case–control
Depressed patients vs. healthy controls
Suicidal depressed (28)
Non-suicidal depressed (49)
Control (95)
Suicide attempt Plasma
(pg/ml)
Suicidal depressed: 386.61 (362.39)
Non-suicidal depressed: 689.66 (404.65)
Control: 819.20 (347.05)
<0.001 None
Lee & Kim (2009) Case–control
Suicidal depressed patients vs. non-suicidal depressed patients vs. healthy controls
Suicidal depressed (20)
Non-suicidal depressed (20)
Control (20)
Suicide attempt Plasma d
(pg/ml)
Suicidal depressed: 713.04 (236.56)
Non-suicidal depressed: 693.98 (347.84)
Control: 709.05 (172.12)
0.971 None
  1. aMean BDNF values estimated from inspection of graph
  2. b3 diagnosis groups: Recurrent depressive disorder, personality disorder, adjustment disorder
  3. cMedians and interquartile ranges presented instead of means and SD
  4. dBDNF was measured in 3 types of sample: platelet-rich plasma, platelet-poor plasma, and platelets. Results are presented here for only the platelet-poor plasma measurement
  5. Abbreviations: BDNF brain-derived neurotrophic factor, SD standard deviation, MDD major depressive disorder, PFC prefrontal cortex, PMI postmortem interval, BLA basolateral amygdala, CeA central nucleus of the amygdala, RDD recurrent depressive disorder, PD personality disorder, AD adjustment disorder, PPAD postpartum affective disorder, CSF cerebrospinal fluid