Clinical Predictors for Venous Thromboembolism in Patients With a History of Thrombosis (PREDICTORS)

Clinical Predictors for Venous Thromboembolism in Patients With a History of Thrombosis

Patients with a history of blood clots are at risk of developing additional clots in the future. Doctors use a tool called a clinical decision rule to tell them how likely it is that a patient has a blood clot and if they should have further testing to look for the clot. This tool may cause doctors to over-diagnosis a recurrent clot because the symptoms may be left over from the previous clot. Correctly diagnosing a recurrent blood clot is very important since there are risks associated with both over-diagnosis and under-diagnosis. If a recurrent blood clot is missed (under-diagnosis) the patient is at risk of death from a clot in the lungs. If blood thinners are prescribed when they are not needed (over-diagnosis), the patient may have to take blood thinners for their lifetime and risk having serious bleeding.

Several tools have been developed to standardize the diagnostic management of a suspected first blood clot. One of these tools is the use of a clinical decision rule. Clinical decision rules have been designed to help clinicians make diagnostic and therapeutic decisions at the bedside. A score is computed on the presence of some criteria from the patient's medical history, clinical signs and symptoms. The score provides the probability of a blood clot. The rules can be used in combinations with a simple blood test - called D-dimer - to identify patients at low risk who don't require diagnostic imaging testing. Benefits include reduced costs, length in hospital and radiation exposure.

Patients with prior blood clots have been shown to be less likely to benefit from the non-invasive testing. Therefore, they often need to undergo imaging tests, which are frequently difficult to interpret in patients with prior blood clots since residual clots are often present and are difficult to distinguish from a recurrent clot.

The objective of this study is to try to prospectively assess the role of existing clinical decision rules in patients with prior blood clots, and to attempt to improve them in order to increase the yield of non-invasive testing and to reduce the risk of over-diagnosis with imaging tests.

With respect to this study, clots within the deep veins of the legs are called deep vein thrombosis (DVT), while clots in the lungs are called pulmonary embolism (PE).

Inclusion Criteria:

• Outpatients with clinically suspected acute recurrent DVT or PE regardless of whether the previous event was a DVT or PE
• Age ≥18 years old
• Willing and able to give informed consent

Exclusion Criteria:

• Life expectancy less than 3 months
• Suspicion of upper extremity thrombosis or thrombosis at an unusual site (e.g. cerebral or abdominal venous thrombosis)
• Previous VTE was distal DVT or subsegmental PE
• Suspected recurrent VTE is asymptomatic
• Previously enrolled in this study