From the Guidelines
If you suspect a blood clot, you should seek immediate medical attention rather than trying to rule it out yourself, as a healthcare provider will evaluate your symptoms and risk factors, then order appropriate tests, such as a D-dimer blood test and imaging studies like ultrasound or CT pulmonary angiogram, to determine the best course of action 1. To rule out a blood clot, a healthcare provider will typically start by evaluating your symptoms and risk factors, then order a D-dimer blood test, which measures a substance released when blood clots break down, and imaging studies such as:
- Ultrasound for suspected deep vein thrombosis (DVT)
- CT pulmonary angiogram for suspected pulmonary embolism Other tests might include venography or MRI depending on the suspected location of the clot. Some key points to consider when ruling out a blood clot include:
- A negative D-dimer result in a highly sensitive assay safely excludes PE in patients with a low or moderate clinical probability, while a moderately sensitive assay excludes PE only in patients with a low clinical probability 1
- Compression ultrasonography and computed tomographic venography can also be used to diagnose DVT, with a sensitivity over 90% for proximal DVT and a specificity of about 95% 1
- Age-adjusted d-dimer thresholds (age × 10 ng/mL rather than a generic 500 ng/mL) should be used in patients older than 50 years to determine whether imaging is warranted 1
- Clinicians should not obtain any imaging studies in patients with a d-dimer level below the age-adjusted cutoff 1 Common warning signs that warrant urgent medical attention include:
- Swelling, pain, warmth, and redness in a limb for DVT
- Sudden shortness of breath, chest pain, rapid heart rate, and coughing up blood for pulmonary embolism While waiting for medical care, avoid massaging the affected area or taking aspirin without medical guidance, as these actions could potentially worsen the situation. It's also important to note that a negative scan for a lower extremity DVT does not rule out the presence of pulmonary embolism, and failure to arrange for repeat venous evaluation in patients with suspicion for isolated calf or distal DVT can lead to missed diagnoses 1
From the Research
Ruling Out Blood Clot
To rule out a blood clot, several diagnostic methods can be employed, including:
- Clinical probability assessment
- D-dimer measurement
- Compression ultrasonography
- Multidetector computed tomography (CT) angiography
- Venography
- Plethysmography
- Doppler flow studies
- Radioisotope tests
- Thermography
- Peripheral blood tests
Diagnostic Approaches
The selection of an appropriate diagnostic modality depends upon institutional capabilities, cost-effectiveness, and individual patient circumstances 2. An algorithm strategy combining pretest probability, D-dimer testing, and compression ultrasound imaging allows for safe and convenient investigation of suspected lower-extremity thrombosis 3.
Non-Invasive Diagnostic Algorithms
Non-invasive diagnostic algorithms have been developed that include clinical probability assessment and D-dimer measurement, which allow the selection of patients who require non-invasive imaging 4. These initial steps enable the identification of patients who require further testing, such as compression ultrasonography or multidetector computed tomography (CT) angiography.
Incidental Findings
Venous ultrasound testing can also diagnose other causes of leg pain or swelling, and may detect incidental findings, including pseudoaneurysm, arterial occlusive disease, vascular graft complication, compartment syndrome, and tumor 5. These findings can be clinically significant and may require immediate treatment.
Diagnostic Imaging
Diagnostic imaging modalities, such as CT venogram and inferior vena cavagram, can be used to evaluate for thrombus in or around an inferior vena cava (IVC) filter 6. These imaging modalities can help identify patients at high risk for venous thromboembolism recurrence and complications.