Blood Clots (cont.)
Exams and Tests
The initial step in making the diagnosis of a blood clot is obtaining a history. Since patients rarely are able to state that they have a blood clot, the health care practitioner will ask questions about what might be occurring. If a blood clot or thrombus is a consideration, the history may expand to access the patient's risk factors or situations that might have put the patient at risk for forming a clot.
- Venous blood clots (venous thrombus) often develop slowly with gradual swelling, pain, and discoloration of the involved area and the symptoms will progress over hours.
- An arterial thrombi occurs as an acute event. Tissues need oxygen immediately, and the loss of blood supply as a result of an arterial clot creates a situation in which symptoms begin immediately.
Physical examination will help add information to increase the suspicion for a blood clot.
- Venous thrombi may cause swelling of an extremity. It may be red, warm, and tender and sometimes difficult to distinguish from cellulitis or an infection of the extremity. If there is concern about a pulmonary embolus, the examiner may listen to the lungs looking for abnormal sounds caused by an area of inflamed lung tissue.
- Arterial thrombus is much more dramatic. If a leg or arm is involved, the tissue may be white because of the lack of blood supply. As well, it may be cool to touch and there may be loss of sensation and movement. The patient may be writhing in pain. Arterial thrombus is also the cause of heart attack and stroke.
Testing for venous blood clots
- Ultrasound: Venous blood clots may be detected in a variety of ways, although ultrasound is most commonly used. Occasionally, the patient's size and shape limit the ability for ultrasound to give a definitive answer.
- Venography: Venography may be another alternative to look for a clot. A radiologist injects contrast dye into a small vein in the hand or foot, and using fluoroscopy (video X-ray) watches the dye fill the veins in the extremity as it travels back to the heart.
- Blood tests: Sometimes, a blood test is used to screen for blood clots. D-dimer is a breakdown product of a blood clot, and levels of this substance may be measured in the bloodstream. Blood clots are not stagnant; the body tries to dissolve them at the same time as a new clot is being added. D-dimer is not specific for a blood clot in a given area and cannot distinguish the difference between a "good" (necessary) blood clot (one that forms after surgery or due to bruising from a fall) from one that is causing problems. It is used as a screening test with hopes that the result is negative and shows that there is no need to look further for blood clots.
- Imaging: Should a blood clot embolize to the lung, this may be a medical emergency. There are a variety of tests to look for pulmonary emboli. A plain chest X-ray will not show blood clots, but may be done to look for other conditions that can cause chest pain and shortness of breath, the symptoms of the embolus. The electrocardiogram (EKG) may show abnormalities suggestive of a pulmonary embolus and may also show other reasons for chest pain.
Computerized tomography (CT) is often the test of choice when suspicion of pulmonary embolus is high. Contrast is injected intravenously, and the radiologist can determine whether a clot is present.
On occasion, ventilation perfusion (V/Q) scans are performed to look for pulmonary emboli. This test uses labeled chemicals to identify inhaled air into the lungs and match it with blood flow in the arteries. It is less accurate than a CT scan and is subjective to variances in interpretation.
Testing for arterial blood clots
Arterial thrombosis is an emergency, since tissue cannot survive very long without blood supply before there is irreversible damage. In an arm or leg, often a surgeon is immediately consulted. Arteriography may be considered. Arteriography is a technique in which dye is injected into the artery in question to look for blockage. Sometimes, if there is a large artery that is occluded, this test is done in the operating room with the presumption that a surgical procedure will be necessary to open the vessel and restore blood flow.
For an acute heart attack, the EKG may confirm the diagnosis, although blood tests may be used to look for enzymes (troponin, myoglobin, CPK) that leak into the bloodstream from irritated heart muscle. With an acute heart attack, the diagnostic and therapeutic procedure of choice is a heart catheterization.
For an acute stroke (cerebrovascular accident, CVA), the test of choice is a computerized tomography (CT) scan of the head to look for bleeding or tumor as the cause of stroke symptoms. If the stroke symptoms resolve, meaning that atransient ischemic attack (TIA) has occurred, tests may include carotid ultrasound to look for blockage in the major arteries of the neck and echocardiography to look for blood clots in the heart that may embolize to the brain.
Medically Reviewed by a Doctor on 5/27/2014
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