CT scans: when they help and what they can show

A CT scan, also known as a computed tomography scan, uses X-rays to create detailed cross-sectional images of the body. In UK general practice, CT scans are used selectively when rapid, detailed imaging is needed to assess potentially serious conditions or to guide urgent decision-making.

This page explains how CT scans are used, what they are particularly good at, the associated radiation considerations, and how GPs decide when a CT scan is appropriate.

These articles are intended as educational sources, not diagnostic nor taking place of a proper medical assessment. If you need help or advice on medical scans, please book a GP appointment.

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How CT scans are used in GP care

CT scans are most useful when a GP needs:

Detailed imaging quickly
A broad overview of an internal area
Assessment of conditions that may not be visible on X-ray or ultrasound alone

CT is commonly used to support urgent referral pathways or hospital assessment rather than routine investigation of mild symptoms.

Seek urgent medical advice if you develop:

Severe chest pain or sudden breathlessness
Sudden weakness, confusion, or collapse
Severe abdominal pain with fever or vomiting
Signs of internal bleeding

What a CT scan can and cannot show

What CT scan is useful for

CT scans are particularly helpful for assessing:

The chest, including lungs and mediastinum
The abdomen and pelvis, including organs and blood vessels
Complex injuries following trauma
Internal bleeding
Some cancers, depending on context
Acute neurological conditions in selected cases

CT provides more detail than standard X-ray and is often used in acute or complex presentations.

What CT scans are less helpful for

CT may not be the best test for:

Soft tissue detail in joints or nerves, where MRI is often superior
Mild or early musculoskeletal pain
Functional conditions without structural abnormality

The choice of imaging depends on the clinical question being asked.

Common reasons a GP may recommend a CT scan

Chest symptoms

A CT scan may be considered for:

Persistent or unexplained breathlessness
Concerning chest symptoms following abnormal tests
Assessment of lung pathology where X-ray is insufficient

Abdominal or pelvic symptoms

CT may be used for:

Severe or persistent abdominal pain
Suspected appendicitis, diverticulitis, or bowel obstruction
Assessment of abdominal masses or internal bleeding

Neurological or head symptoms

In some cases, CT is used to:

Rapidly assess acute neurological symptoms
Exclude serious causes such as bleeding

These situations often involve urgent referral rather than routine GP management.

How a GP decides whether a CT scan is appropriate

A GP will consider:

The urgency and severity of symptoms
Whether rapid imaging is required
Whether CT findings would change management immediately
Whether a different imaging test is safer or more appropriate

For the GP approach to imaging decisions, see:
How GPs use medical imaging in practice

Radiation and safety considerations

CT scans use higher doses of ionising radiation than standard X-rays. While the risk from a single scan is small, it is still an important consideration.

GPs are cautious with CT scans because:

Radiation exposure accumulates over time
Many symptoms can be managed safely without CT
Imaging should be justified by clear clinical benefit

CT scans are recommended when the expected benefit outweighs the potential risk.

Contrast CT scans

Some CT scans involve contrast dye to improve image clarity.

Contrast may help assess:

Blood vessels
Inflammation or infection
Tumours or masses

Contrast is generally safe but may not be suitable for everyone. Kidney function and allergy history are considered before use.

Limitations and common misunderstandings

A normal CT scan does not rule out all disease

Some conditions may not be visible early or may require different imaging.

Abnormal findings may be incidental

CT scans can reveal unrelated findings that are not causing symptoms. These often require careful interpretation rather than immediate action.

A GP’s role is to contextualise CT findings and guide next steps appropriately.

What happens after a CT scan

If the CT explains symptoms

A GP may:

Arrange urgent referral or hospital assessment
Coordinate further tests or specialist input
Adjust management plans

If the CT is normal