From the Guidelines
A CT angiography (CTA) of the chest is indicated to rule out pulmonary embolism (PE) in patients with high pretest probability of PE, as recommended by the American College of Physicians 1. The primary indications for CTA include unexplained dyspnea, chest pain, tachycardia, hypoxemia, or hemoptysis, especially when combined with risk factors such as immobilization, recent surgery, cancer, pregnancy, oral contraceptive use, or known thrombophilia.
- The Wells score or PERC rule can help determine pre-test probability; a Wells score >4 or positive D-dimer test in lower-risk patients warrants CTA imaging 1.
- CTA is preferred over V/Q scanning in most cases due to its higher sensitivity (85-90%) and specificity (90-95%), ability to visualize clots directly, and capacity to identify alternative diagnoses 1.
- Before ordering CTA, ensure the patient has adequate renal function (eGFR >30 ml/min) to tolerate contrast and no severe contrast allergy.
- Patients should be informed about radiation exposure and the need for IV contrast.
- CTA is contraindicated in pregnancy unless absolutely necessary, and alternative imaging like V/Q scanning may be considered in such cases or in patients with renal insufficiency 1. CTA should be obtained in patients with high pretest probability of PE, as it is the most sensitive and specific test for diagnosing PE 1.
From the Research
Indications for CTA Chest to Rule Out Pulmonary Embolism
- The primary indication for a CTA (Computed Tomography Angiography) chest is to diagnose or rule out pulmonary embolism (PE) in patients with suspected acute PE 2.
- CTA chest is considered the imaging modality of choice for suspected acute pulmonary embolism due to its speed, reliability, and ability to provide direct visualization of the pulmonary arteries 2, 3.
- The use of CTA chest is particularly useful in patients with a high clinical suspicion of PE, as it can help confirm or exclude the diagnosis 4, 5.
- In patients with indeterminate or negative initial imaging tests despite a high pre-test probability, CTA chest can be used in conjunction with other diagnostic tests, such as ventilation-perfusion scanning, to provide a definitive diagnosis 4, 6.
Diagnostic Accuracy and Safety
- CTA chest has been shown to be highly sensitive and specific for the diagnosis of pulmonary embolism, making it a reliable tool for ruling out PE in patients with negative results 2, 3.
- However, CTA chest is associated with significant radiation exposure, which may increase the risk of secondary malignancies, particularly in young women 3.
- Alternative diagnostic tests, such as ventilation-perfusion scanning, may be preferred in certain patient populations, such as those with renal insufficiency or a high risk of radiation exposure 4, 3, 5.
Clinical Guidelines and Recommendations
- Clinical guidelines recommend the use of CTA chest as the primary imaging modality for suspected acute pulmonary embolism, particularly in patients with a high clinical probability or positive D-dimers 5.
- The choice of diagnostic test should be guided by the patient's clinical probability, with CTA chest being the preferred test in patients with a high clinical probability or positive D-dimers 5.
- In patients with contra-indications to CTA chest, such as renal insufficiency, alternative diagnostic tests, such as ventilation-perfusion scanning or lower limb venous compression ultrasound, may be used 5.