A blood clot, particularly if it detaches and enters the bloodstream, may cause a low grade or mild fever. In addition to elevated body temperature, the symptoms of fever include sweating or shivering, a persistent headache, body weakness, dehydration and diminished appetite.
In severe cases, fevers can cause additional symptoms, including irritability and mood disturbances, confusion, convulsions or even hallucinations. These symptoms usually occur if the body’s core temperature settles in a very high range, between 103 and 106 degrees Fahrenheit (39.4 and 41.1 degrees Celsius).
Oftentimes the skin surrounding the clot, even though it’s deep within the leg, may become quite tender to the touch with no evidence of bruising on the skin’s surface. The veins below the skin in the affected area may also become visible through the skin, although this typically does not occur until the blood clot reaches a relatively large size.
Note that tenderness may occur in both legs, even if only one leg is affected by the blood clot. This may be because you’re subconsciously favoring your stronger leg, which in turn can trigger muscle and joint strains that subsequently manifest through pain and tenderness.
Approximately half of those experiencing a blood clot in the leg (or deep vein thrombosis) have little or no symptoms at all. While an asymptomatic blood clot is usually a sign that the thrombosis has not yet reached a serious stage, this isn’t always the case. Even large blood clots that require immediate medical attention can sometimes cause no symptoms at all until the clot dislodges and travels through the bloodstream.
This is one of the reasons it’s important to actively prevent blood clots if you’re at elevated risk. Wear comfortable, loose-fitting clothing, avoid standing or sitting for periods exceeding one hour, lower your salt intake and remain physically active.