The US research raises the controversial prospect of a blood test providing early warning of suicide attempts.
One particular molecule, an enzyme called SAT1, was linked to suicidal tendencies in a group of patients with bipolar disorder, a mental illness characterised by episodes of extreme high and low moods.
Three other markers showed a weaker association.
The elevated blood markers stood out in a subgroup of nine patients who displayed a sudden dramatic shift to powerful suicidal thoughts.
A similar pattern was seen in blood samples taken from nine suicide victims who had succeeded in killing themselves. Finally blood samples were tested from two further groups of patients with bipolar disorder and schizophrenia-type pychoses.
Raised levels of the biomarkers correlated with admissions to hospital after suicide attempts. The link was stronger for bipolar disorder than for schizophrenia.
Study leader Dr Alexander Niculescu, from Indiana University, said: “Suicide is a big problem in psychiatry. It’s a big problem in the civilian realm, it’s a big problem in the military realm and there are no objective markers.
“We need better ways to identify, intervene and prevent these tragic cases.”
The research was published in the journal Molecular Psychiatry