Large blood clots in the legs can cause symptoms such as leg redness and warmth, leg swelling, and leg pain that worsens when standing up or walking, according to ClotCare. While blood clots located below the knee are unlikely to cause complications, clots that start or extend above the knee sometimes break away, travel through the blood and block blood vessels in the lungs, causing a pulmonary embolism.
As ClotCare explains, a pulmonary embolism is a life-threatening condition. Symptoms include difficulty breathing, shortness of breath and chest pain. Immediate medical treatment is required.
Factors that increase the risk of getting a blood clot in the legs include prolonged immobility and bed rest, obesity, varicose veins, cancer, major injuries, long-distance travel, estrogen replacement therapy, and pregnancy and child birth. ClotCare notes that the odds of getting a blood clot in the legs increases as a person ages and doubles with every decade of life over the age of 40. Additionally, some people are genetically prone to develop blood clots.
To prevent blood clots in the legs, ClotCare recommends exercising the legs regularly, maintaining a healthy body weight, avoiding lying in bed or sitting for extended periods of time, and avoiding overly tight, restrictive clothing.