In most cases it is difficult for a doctor to be sure of the diagnosis from just the normal symptoms as there are other causes of a painful and swollen legs. For example, a muscle strain or infection. If you have a suspected DVT you will normally be advised to have tests done urgently to confirm or rule out the diagnosis.
In a low-probability situation of DVT, current practice is to commence investigations by testing for D-dimer levels. This is blood test that detects fragments of the breakdown products of a blood clot. The higher the D-dimer levels, the more likely that you have a blood clot in a vein. This cross-linked fibrin degradation product is an indication that thrombosis is occurring, and that the blood clot is being dissolved by plasmin. A low D dimer level should prompt other possible diagnoses (such as a ruptured Baker's cyst, if this has not been considered as part of the history).
Other blood tests usually performed at this point are:
· Complete blood count
· Primary coagulation studies: PT, APTT, Fibrinogen
· Liver enzymes
· Renal function and electrolytes
Compression ultrasound scanning of the leg veins, combined with duplex measurements (to determine blood flow), can reveal a blood clot and the extent of it (i.e. whether it is below or above the knee) is often used to complement the above tests.
Sometimes these tests are not 100% conclusive and more detailed tests are necessary. The gold standard is intravenous venography, which involves injecting a peripheral vein of the affected limb with a contrast agent and taking X-rays, to reveal whether the venous supply has been obstructed. Because of its invasiveness, this test is rarely performed.
Another Test that can also be used is impedance phlebography, which is a non-invasive medical test that measures small changes in electrical resistance of the chest, calf or other regions of the body. These measurements reflect blood volume changes, and can indirectly indicate the presence or absence of venous thrombosis. This procedure provides an alternative to venography, which is invasive and requires a great deal of skill to execute adequately and interpret accurately.
For leg veins, the test measures blood volume in the lower leg due to temporary venous obstruction. This is accomplished by inflating a pneumatic cuff around the thigh to sufficient pressure to cut off venous flow but not arterial flow, causing the venous blood pressure to rise until it equals the pressure under the cuff. When the cuff is released there is a rapid venous runoff and a prompt return to the resting blood volume. Venous thrombosis will alter the normal response to temporary venous obstruction in a highly characteristic way, causing a delay in emptying of the venous system after the release of the tourniquet. The increase in blood volume after cuff inflation is also usually diminished.
Doctors are starting to use a system known as Probability scoring: In 2006, Scarvelis and Wells developed a set of clinical criteria for DVT, on the heals of a widely adopted set of clinical criteria for pulmonary embolism.
Wells criteria:- (mnemonic: C3PO+R2D2): Cancer (active), Calf diameter increase >3 cm, Collateral superficial veins visible, Pitting oedema, Previous DVT documented, Oedema of the whole leg, tenderness of the calf, Recent surgery, Recent immobilization, Different diagnosis more likely (subtract 2 points).
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