UK scientists have developed a blood test to help doctors pick the best drug for patients with depression, reports BBC.

Medics currently have to rely on trial and error, meaning around half of the time the first type of antidepressant given fails to work. The researchers from King's College London say checking a patient's blood could help identify accurate treatment. Those who test positive for inflammation need more aggressive therapy from the outset, they say.

The blood test, described in the International Journal of Neuropsychopharmacology, is the culmination of years of investigation. It looks for two specific markers of inflammation — a compound called macrophage migration inhibitory factor (MIF) and another called interleukin-1beta.

In the study, patients with high levels of these markers were unlikely to respond to conventional, commonly prescribed SSRI and tricyclic antidepressants.

Lead researcher Prof Carmine Pariante said, "About a third of patients might have these inflammatory markers and they would be people we might encourage to go on more aggressive treatment." Anti-depressants are safe but they can have side effects.