A teacher from the U.K. saved her student's life after diagnosing a potentially fatal blood clot in her leg, The Sun reported.

Billie-Jo Twigg, 19, told her college professor she thought she pulled a muscle because her leg started to swell up.

Caroline Morgan, who was teaching Twigg's biology class at Portsmouth College in Hampshire, southern England, immediately recognized the symptoms as deep vein thrombosis (DVT).

She told Twigg to go to the doctor, who then sent her for an ultrasound that revealed three dangerous blood clots.

Deep vein thrombosis is a condition in which a blood clot forms in one or more of the deep veins in your body, usually in your legs, the Mayo Clinic said on its Web site. If left untreated, the clots could have traveled to her lungs and killed her.

"If Caroline had not said anything I would have just left it and waited for it to get better itself," Twigg said. "But I went and got it checked out anyway and was told to get to the hospital straight away. Caroline telling me to go to a doctor literally saved my life and I can't thank her enough."

Click here to read more form The Sun.