How to read a chest X‑ray

Written by the X-Ray Atlas editorial team from the sources listed below · Medical review pending · Updated 24 October 2026 · Level: Beginner

The chest X-ray (CXR) is the most requested imaging test in medicine, and often the first person to look at it is not a radiologist. Spotting the obvious abnormality is rarely the problem. The usual failure is stopping too early, missing the second finding, the misplaced tube, or the small apical pneumothorax. A fixed system protects you from that. This guide teaches the approach used by most UK and international teaching programmes: pre-checks → image quality (RIPE) → ABCDE → review areas → summary.

1. Before you look: pre-checks

Thirty seconds of checking saves the most embarrassing errors:

• Right patient, right film. Name, date of birth or hospital number, and the date and time of the exposure. With several films a day on ICU, reading the wrong one is a real error.
• Previous imaging. Comparison is the most powerful tool in radiology. A "new" mass that has been unchanged for five years is a very different problem.
• Projection and position. PA or AP? Erect, semi-erect or supine? The label usually tells you. If not, the scapulae and clavicles do (see below).
• Side marker. Confirm left and right from the marker, then from the anatomy: the cardiac apex and gastric bubble are normally on the left. A mismatch should make you think of dextrocardia or situs inversus, or a wrongly placed marker.
• The clinical question. Why was the film requested? You should answer it explicitly at the end.

2. Is the film adequate? RIPE

Poor technique creates false findings and hides real ones, so assess quality before interpreting anything.

Check	How to assess	Why it matters
Rotation	The medial ends of the clavicles should be equidistant from the spinous process at the same level.	Rotation distorts the mediastinal outline, can make one hilum look prominent and alters the density of each lung.
Inspiration	Count ribs above the mid-point of the right hemidiaphragm: roughly 6 anterior or 8–10 posterior ribs indicates a good inspiration.	A poor breath crowds the lung markings, mimicking basal shadowing, and makes the heart and mediastinum look wider. More than about 7 anterior ribs suggests hyperinflation (for example COPD or asthma).
Projection	PA: scapulae projected clear of the lungs, clavicles fairly horizontal. AP: scapulae overlap the lungs, clavicles project higher.	On an AP film the heart is magnified, so heart size cannot be reliably judged.
Exposure	On a well-penetrated PA film the thoracic vertebral bodies are just visible through the heart.	Under-exposure (too white) hides the retrocardiac region and mimics consolidation. Over-exposure (too dark) hides nodules and can mimic emphysema.

Also check coverage: both apices, both costophrenic angles and the lateral chest walls must be on the film. If they aren't, say so. A pneumothorax or effusion can sit exactly in the missing part.

3. The ABCDE approach

A — Airway

• Trachea: is it central? It is pushed away by a tension pneumothorax, a large effusion or a mass, and pulled towards collapse, previous pneumonectomy or fibrosis. A slight rightward deviation at the aortic knob is normal.
• Carina and main bronchi: look for splaying of the carina and narrowing or cut-off of a bronchus.
• Tubes: if there is an endotracheal tube, locate its tip relative to the carina. See ETT position.

B — Breathing (lungs and pleura)

• Compare the lungs zone by zone, left with right: upper, middle and lower zones. Zones are descriptive regions of the film and do not correspond to lobes. Asymmetry is easier to see than absolute abnormality.
• Look for areas of increased density (consolidation, collapse, mass, effusion) and decreased density (pneumothorax, bullae, hyperinflation, mastectomy).
• Trace the pleural edge all the way round. A visceral pleural line with no lung markings beyond it is a pneumothorax.
• Check the costophrenic angles: blunting is often the first sign of a pleural effusion.
• Assess lung volumes: are they small (fibrosis, poor effort) or large (COPD)?

C — Circulation (heart, mediastinum and hila)

• Heart size: on a PA film, the cardiothoracic ratio (CTR) is the maximum horizontal cardiac width divided by the maximum internal thoracic width. A CTR above 0.5 suggests cardiomegaly. Do not apply this to an AP film, where the heart is magnified.
• Heart borders: the right border is the right atrium, and the left border is mostly the left ventricle. Loss of a border means something of soft-tissue density is touching it (the silhouette sign). Loss of the right heart border points to the right middle lobe, and loss of the left heart border to the lingula.
• Mediastinum: follow the aortic knob, the aortopulmonary window (normally a concave notch) and the right paratracheal stripe. A widened mediastinum after trauma should raise concern for aortic injury.
• Hila: compare position, size and density. The left hilum is normally level with or higher than the right. The right hilum should not sit higher than the left, so if it does, suspect volume loss above it on the right or below it on the left. See mediastinum and hila.

D — Diaphragm

• The right hemidiaphragm usually sits slightly higher than the left (by up to about 1.5–2 cm).
• Both outlines should be sharp. Loss of the right hemidiaphragm outline points to the right lower lobe, and loss of the left to the left lower lobe.
• Look under the diaphragm for free gas. A crescent of air beneath the hemidiaphragm on an erect film suggests pneumoperitoneum. Don't confuse the gastric bubble or interposed colon (Chilaiditi sign) with free air.

E — Everything else

• Bones: ribs (trace each one, including the posterior ends), clavicles, scapulae, spine and proximal humeri. Look for fractures, lytic or sclerotic lesions and old injuries.
• Soft tissues: surgical emphysema, breast shadows, mastectomy.
• Lines, tubes and devices: name every device and check where its tip is: ETT, NG tube, central lines, drains, pacemakers. See the lines and tubes modules.

4. Review areas: where findings hide

Most missed findings on chest films sit in a handful of places. Check each one deliberately, after you think you have finished:

1. Apices: small pneumothoraces, Pancoast tumours, TB. Overlapping ribs and clavicles make this area hard.
2. Behind the heart: left lower lobe collapse ("sail sign") or consolidation, hiatus hernia, masses. The retrocardiac region should be about as dark as the lung above it, and the descending aorta outline should be visible.
3. Hila: subtle masses and lymphadenopathy.
4. Below the diaphragm: free gas, and lung bases that extend posteriorly below the dome of the diaphragm. Nodules can hide here.
5. Costophrenic angles and lung edges: small effusions and pneumothoraces.
6. Edges of the film and bones: fractures, lytic lesions, the shoulder joints.

5. Presenting the film

Whether it's an OSCE or a handover, use a fixed structure:

If the film shows something that needs immediate action, such as a tension pneumothorax or an NG tube in the airway, say that first. See how to present an X-ray.

6. Common pitfalls

• Calling cardiomegaly on an AP film: the heart is magnified on AP and supine films.
• Skin folds mimicking pneumothorax: a skin fold usually extends beyond the chest wall and has lung markings on both sides of it. The medial border of the scapula can also mimic a pleural edge. See artefacts and mimics.
• Nipple shadows mimicking nodules: they are often bilateral and symmetrical. If in doubt, repeat with nipple markers.
• Supine films: air rises anteriorly and fluid layers posteriorly. A pneumothorax may show only as a deep, lucent costophrenic angle (the deep sulcus sign), and an effusion may show only as a hazy veil over the whole hemithorax.
• A normal chest X-ray does not exclude pulmonary embolism, early pneumonia or small pneumothoraces. Match the test to the question.

Red flags: act now

What to focus on, by role

Role	Priorities
Medical student	A rehearsed system you can say aloud, RIPE, ABCDE and the review areas. Learn the "big five" well: pneumothorax, effusion, consolidation, collapse and heart failure.
Nurse	Recognise the films that need escalation: pneumothorax after line insertion, free air, and tube or line position. Know your local policy on who may confirm an NG tube position.
Junior doctor	Act before the formal report: tension, free air, line position, and the patient who needs CT rather than another film. Document your interpretation.
Radiographer	Image quality and repeat criteria, coverage, projection labelling, and preliminary clinical evaluation of the obvious acute abnormality.
Advanced / FRCR	Lobar collapse patterns, subtle hilar and mediastinal contours, and normal-or-abnormal decisions at speed. Try the rapid reporting mode.

Practise on real chest X-rays →

References

1. Radiology Masterclass. Chest X-ray quality: projection, rotation, inspiration, penetration. radiologymasterclass.co.uk
2. Radiology Masterclass. Chest X-ray anatomy. radiologymasterclass.co.uk
3. Life in the Fast Lane (LITFL). Chest X-ray interpretation. litfl.com
4. Felson B. Chest Roentgenology. Philadelphia: WB Saunders; 1973 (origin of the silhouette sign).
5. Roberts ME, et al. British Thoracic Society Guideline for pleural disease. Thorax 2023;78(Suppl 3):s1–s42. brit-thoracic.org.uk
6. Royal College of Radiologists. iRefer: making the best use of clinical radiology. irefer.org.uk

For education only. Not a substitute for a formal report, senior review or your local policy. Never use this page to make decisions about a real patient.