What primary care conditions require a computed tomography (CT) scan as the first line of diagnostic imaging and should it be with or without contrast?

From the Guidelines

In primary care, CT scans are used as the first line of diagnostic imaging for several acute conditions, with the choice between contrast and non-contrast depending on the suspected pathology, prioritizing conditions that significantly impact morbidity, mortality, and quality of life. The decision to use CT scans with or without contrast is guided by the specific clinical scenario, considering the benefits and risks of contrast administration, as well as the patient's renal function, history of contrast allergies, and metformin use 1.

Common Primary Care Conditions Requiring CT Scans

• Acute Appendicitis: CT with intravenous (IV) contrast is usually appropriate, but CT without IV contrast also has high diagnostic accuracy and may be appropriate in certain situations 1.
• Suspected Kidney Stones: Non-contrast CT is preferred to rapidly identify calcifications without delay 1.
• Pulmonary Embolism: Contrast-enhanced CT (CT pulmonary angiography) is the first choice to visualize vascular structures and inflammatory changes.
• Acute Aortic Dissection: Contrast-enhanced CT is essential to highlight abnormal tissue enhancement and visualize vascular structures.
• Diverticulitis and Abdominal Abscesses: Contrast-enhanced CT is the first choice to visualize inflammatory changes and vascular structures.
• Trauma Patients: Non-contrast CT is initially used to assess for acute bleeding or fractures, with contrast studies potentially added later.

Considerations for Contrast Administration

• Patient's renal function (eGFR preferably >45 ml/min/1.73m²) 1.
• History of contrast allergies, which may require pre-medication with corticosteroids and antihistamines.
• Metformin use, which may require temporary discontinuation.
• Patients should be well-hydrated before contrast administration to reduce kidney injury risk. Some of the evidence may not be directly related to the question, but the most recent and highest quality study, 1, provides guidance on the use of CT scans in primary care, particularly for acute appendicitis.

From the Research

Primary Care Conditions Requiring CT Scan as First Line Diagnostic Imaging

• Acute appendicitis: CT scan with or without contrast can be used as the first line of diagnostic imaging for acute appendicitis, with studies showing no significant difference in diagnostic accuracy between non-enhanced CT (NECT) and contrast-enhanced CT (CECT) 2, 3
• Acute pulmonary embolism: Pulmonary CT angiography (CTA) is the imaging modality of choice for suspected acute pulmonary embolism, typically requiring contrast medium 4
• Other conditions: CT scans are commonly used as the first line of diagnostic imaging for various other conditions, including emergencies, cardiovascular, pulmonary, gastrointestinal, endocrine, neurological, and orthopedic applications, often with contrast media 5

Use of Contrast in CT Scans

• Acute appendicitis: Both NECT and CECT can be used, with NECT providing comparable diagnostic accuracy without the need for contrast media, which may be beneficial for patients with contraindications to iodinated contrast media 2
• Acute pulmonary embolism: Contrast medium is typically required for pulmonary CTA 4
• Other conditions: The use of contrast media in CT scans depends on the specific condition being diagnosed and the clinical judgment of the radiologist 5

Diagnostic Accuracy of CT Scans

• Acute appendicitis: CT scans have high sensitivity and specificity for diagnosing acute appendicitis, with summary sensitivity and specificity estimates ranging from 0.91 to 0.96 and 0.93 to 0.95, respectively 3
• Acute pulmonary embolism: Pulmonary CTA has high diagnostic accuracy for suspected acute pulmonary embolism, with continued developments in CT system hardware and postprocessing techniques aiming to improve image quality and diagnostic accuracy 4
• Other conditions: CT scans have a significant clinical impact and are widely used for various applications, with ongoing technological developments aiming to improve image quality, diagnostic accuracy, and patient management 5