A study has found that half of the teenagers who screened positive for depression got better within six weeks without treatment.

Two aspects of the teens' conditions seemed to predict whether the depression would ease without treatment: the severity of the symptoms and whether the symptoms persisted for six weeks, according to an article published in the journal Pediatrics. The researchers looked at other factors, including substance abuse, family history and abuse, but they did not predict which adolescents would stay depressed.

The issue is important because in 2009 the U.S. Preventive Services Task Force recommended screening adolescents for depression in primary care settings. The goal is to avoid unnecessary treatment for those with transient symptoms.

"As we institute broad-based screening of adolescents in primary care settings, we are likely to encounter an increased number of youth who have short episodes of depression that resolve with monitoring and support," the researchers wrote.

An estimated 12 percent of girls and 4.5 percent of boys had a major episode of depression in the past year.

The researchers noted there's a need to figure out which young people need treatment and which just need "watchful waiting" after their primary care provider identifies depression. Teenagers who are suicidal or who have significant functional impairment should be treated.