You can tell if you have a blood clot or a leg cramp by the look of the leg. A blood clot will often cause the leg to be tight, hot, swollen and reddish or purplish in color. A vascular ultrasound will determine the location of the clot.
what are the symptoms of a blood clot in the legs? – http://www.ehow.com/about_5105982_symptoms-blood-clot-legs.html