The correct answer is:

The guidelines only provide indications for imaging in general without specifying a preferred imaging modality for a given situation (e.g. chest x-ray versus CT scan).

Key Point:

Whether a chest x-ray or a CT scan is chosen to image the lungs of confirmed and presumed COVID-19 patients during the pandemic depends on a large number of considerations besides the clinical benefit of chest x-ray versus CT scan, for example, the consumption of PPE, number of personnel exposed, number of disinfecting procedures, and length of imaging non-availability between patients for each imaging choice.

Explanation:

The guidelines address imaging indications for 3 common COVID-19 scenarios but leave the choice of imaging modality to clinical teams, who should take into account not just the pros and cons of a given modality per se, but also local resources and patient volume.

The guideline for imaging suspected/confirmed COVID-19 patients recommends:

1. Mild Disease – Imaging Rarely Necessary: In patients with suspected or proven COVID-19 and mild clinical disease, imaging is only indicated if known risk factors for disease progression are present. In this subset of patients, imaging provides a baseline for future comparison and may also show the current state of pertinent (e.g. cardiac) comorbidities.

• When choosing an imaging modality for this group, the following can be considered: a chest-x-ray will usually not show early COVID-19 disease, but may show other pre-existing abnormalities.
• A CT scan will show early COVID-19 pulmonary changes (incl. in asymptomatic patients) and will also better delineate certain important cardiac comorbidities (e.g. heart failure).

2.  Moderate to Severe Disease With Positive COVID-19 Test Result  – Imaging Indicated in Patient with Worsening Respiratory Status: Imaging is indicated in a patient with known COVID-19 disease, moderate-to-severe disease, and worsening respiratory status.

• When choosing an imaging modality in this group, the following can be considered: a chest-x-ray will typically show COVID-19 disease and permits monitoring of disease progression; it is a portable study that can be done in the patient’s room, which simplifies infection control, requires less PPE, and exposes less personnel and less hospital rooms/hallways to the patient.
• A CT scan creates a larger COVID-19 dissemination risk/resource burden because the patient must be transported to the CT-scanner. These risks must be weighed against the likelihood that the CT scan will show clinically actionable, additional information over the chest x-ray. For example, in patients with suspected pulmonary thromboembolism, a CT scan with contrast is likely to provide critical additional information for treatment decisions.

3. Moderate to Severe Disease Without a COVID-19 Test Result – Imaging Indicated For Resource-Poor Triage: imaging is indicated specifically for medical triage when a patient presents with moderate to severe clinical features and a high pre-test probability of disease, but no COVID-19 test result.

• In a resource-limited environment, imaging facilitates the rapid triage (e.g. into isolation) of ill patients by providing a presumptive diagnosis of COVID-19 versus another etiology while awaiting a COVD-19 test results for hours or days.

Figures:

COVID-19 Imaging: Chest X-Ray

COVID-19 Imaging: CT

Comparison of CT images between survival group and mortality group. A,B, and C represent the survival group. D,E, and F represent the mortality group.

References:

Rubin GD, Ryerson CJ, Haramati LB, et al. The Role of Chest Imaging in Patient Management during the COVID-19 Pandemic: A Multinational Consensus Statement from the Fleischner Society, CHEST (2020)