Biological predictors of suicidal behaviour in mood disorders

Predicting suicide is difficult due to its low base rate and the multicausal nature of suicidal behaviour. Retrospective and cross-sectional studies have identified a number of biologic abnormalities associated with suicide and non-fatal suicide attempt. Non-fatal suicidal behaviour shows a big range in terms of degree of intent and medical damage or lethality. High intent more lethal suicide attempts are associated with greater risk of suicide and different demographics and biology compared with impulsive low lethality attempts. Prospective studies of suicide provide estimates of the predictive utility of biologic measures. Here, we review prospective studies of suicidal behaviour and serotonergic, noradrenergic, dopaminergic systems, inflammation, polyunsaturated fatty acids, and the hypothalamic–pituitary–adrenocortical (HPA) axis function in mood disorders. The most promising biologic predictors are low cerebrospinal fluid (CSF), 5-hydroxyindoleacetic acid (5-HIAA), and HPA axis dysfunction, as demonstrated by dexamethasone non-suppression where each are associated with a 4.5-fold greater risk of suicide.