Yes, swelling can be a sign of a blood clot. If you have swelling, pain, or tenderness on just one side, then it’s possible you have a blood clot. The skin over the swollen area may also be red and warm to the touch. If you have any of these symptoms or are concerned your swelling could be due to a blood clot, seek medical attention right away. A healthcare professional will be able to determine if there is a clot and start you on treatment.