Bullied teens are twice as likely to take weapons such as guns or knives to school, a new study reveals.

Three factors were linked to greater odds of high school students carrying a weapon during school hours: fighting at school; being threatened or injured at school; and skipping school out of fear for their safety.

"If kids were being bullied, but not in fear of their physical safety, then there was not an increased risk of carrying a weapon," said lead researcher Dr. Andrew Adesman. He is chief of developmental and behavioral pediatrics at Cohen Children's Medical Center of New York in New Hyde Park.

Get Breaking News Delivered to Your Inbox

However, "almost 50 percent of kids who felt all three threats carried a weapon," Adesman said.

School violence is a serious issue in the United States, with 45 reported school shootings in 2015 alone, the researchers said in background notes. Adesman's team wanted to see how peer aggression might influence the likelihood of weapons-carrying.

The researchers used data from the 2015 U.S. Youth Risk Behavior Survey on more than 15,600 teens in grades 9 through 12. The investigators focused on three types of weapons: guns, knives and clubs.

The findings showed that slightly more than one in five students reported being bullied during the past year. Of these kids, a little more than 4 percent said they took a weapon to school in the previous month.

Teens who skipped school because they feared for their safety were more than three times likelier to carry a weapon than kids not abused. Those who had fights at school were more than five times likelier to carry a weapon, the researchers found.

And teens who were threatened or injured at school were nearly six times more likely to take a weapon to school.

Students who faced all three problems were much more likely to be armed at school (46 percent) than teens who weren't bullied (2.5 percent), according to the study.

However, it's not known how often those weapons were used or whether kids who reported being bullied and being armed were also bullies themselves, Adesman said.

But because of the potentially dire consequences, parents should look for signs that their child is being bullied, he advised. Red flags include unexplained injuries, torn clothing, reports of fights at school or reluctance to go to school.

Parents and schools have a role in stopping bullying and helping kids who feel they must arm themselves in self-defense, Adesman said.

The new report was published online Nov. 27 in the journal Pediatrics.

Melissa Holt, an associate professor of counseling psychology at Boston University, said it's essential to identify teens most likely to arm themselves.

Screening in places like pediatricians' offices, mental health clinics and schools can help, said Holt, co-author of an accompanying journal editorial.

Also, "this study highlights the importance of understanding complexities in the link between bullying victimization and functioning," Holt said.

This type of "nuanced approach" is critical when considering what factors might increase the risk for negative consequences, such as drug use, or reduce the risk for negative outcomes, such as parental and peer support, she added.