What are the risks and precautions for patients with a history of pulmonary embolism or deep vein thrombosis undergoing a CT scan with contrast?

From the Guidelines

Patients with a history of pulmonary embolism (PE) or deep vein thrombosis (DVT) should inform their healthcare provider before undergoing a CT scan with contrast, as they may face increased risks. The primary concern is that iodinated contrast agents used in CT scans can potentially increase blood coagulability, though this risk is generally low 1. For these patients, adequate hydration before and after the procedure is essential to reduce risks. If the patient is on anticoagulant therapy such as warfarin, rivaroxaban, apixaban, or enoxaparin, they typically can continue these medications without interruption before the scan. However, for patients with severe renal impairment, the contrast dose may need adjustment or an alternative imaging method might be considered, as contrast can further stress the kidneys 1. Patients should also be monitored for signs of allergic reactions to contrast, which can range from mild (itching, hives) to severe (anaphylaxis). The risk of contrast-induced nephropathy should be assessed, particularly in those with existing kidney disease or diabetes 1. These precautions are important because contrast agents can affect blood viscosity and vessel walls, potentially exacerbating clotting tendencies in patients already predisposed to thrombotic events. Some key points to consider include:

• The use of age-adjusted d-dimer thresholds to determine d-dimer elevation in patients older than 50 years 1
• Developing diagnostic and treatment pathways for patients with a history of multiple CTs for PE 1
• Considering alternative approaches to the work-up of PE, such as lower-extremity venous ultrasonography or V/Q scanning when appropriate 1

From the Research

Risks and Precautions for CT Scan with Contrast

• Patients with a history of pulmonary embolism or deep vein thrombosis undergoing a CT scan with contrast should be aware of the potential risks, including allergic reactions to the contrast agent and bleeding complications due to anticoagulant therapy 2, 3.
• The use of anticoagulants, such as low-molecular-weight heparin (LMWH) or warfarin, is crucial in preventing recurrent thromboembolic events, but it also increases the risk of bleeding complications 2, 4.
• Studies have shown that apixaban, a novel oral anticoagulant, is associated with a lower risk of bleeding and recurrent venous thromboembolism (VTE) compared to warfarin 4, 5.
• However, the choice of anticoagulant therapy should be individualized based on the patient's risk factors, medical history, and renal function 2, 6.

Precautions for Patients with Pulmonary Embolism or Deep Vein Thrombosis

• Patients with a history of pulmonary embolism or deep vein thrombosis should undergo risk stratification to determine the best course of treatment and to minimize the risk of complications 3.
• The use of thrombolytic agents, such as tissue plasminogen activator (tPA), may be considered in patients with massive pulmonary embolism, but it is associated with a higher risk of bleeding complications 2.
• Patients with renal failure may require alternative anticoagulant therapies, such as unfractionated heparin, due to the increased risk of bleeding complications with LMWH or warfarin 2, 6.

CT Scan with Contrast Considerations

• The decision to use contrast agent during a CT scan should be made on a case-by-case basis, taking into account the patient's medical history, renal function, and the potential benefits and risks of the procedure 3.
• Patients with a history of allergic reactions to contrast agents should be premedicated with antihistamines and corticosteroids to minimize the risk of an allergic reaction 3.
• The use of low-osmolar contrast agents may reduce the risk of allergic reactions and bleeding complications compared to high-osmolar contrast agents 6.