Shortness of Breath: Causes, Tests & When to Worry

Seek Emergency CareSudden severe breathlessness at rest, SpO₂ below 92 %, bluish lips or fingertips (cyanosis), or breathlessness with chest pain: call 999/911 immediately.

Causes by Onset Pattern

Onset	Likely Causes
Sudden (seconds–minutes)	Pulmonary embolism, pneumothorax, anaphylaxis, foreign body
Acute (hours)	Asthma attack, acute heart failure, pneumonia, panic attack
Subacute (days–weeks)	Pleural effusion, worsening COPD, anaemia
Chronic (months–years)	COPD, heart failure, obesity, interstitial lung disease

Key Diagnostic Tests

Pulse oximetry (SpO₂): measures oxygen level in blood
Chest X-ray: detects pneumonia, fluid, pneumothorax
ECG: detects cardiac causes including PE clues
Blood tests: FBC (anaemia), D-dimer (PE), BNP (heart failure)
Spirometry: measures lung function for asthma/COPD
CT pulmonary angiogram: confirms PE

Rule of Thirds

Roughly: ⅓ of chronic breathlessness is cardiac, ⅓ is respiratory, ⅓ is other (anaemia, deconditioning, anxiety). A thorough history usually narrows it quickly.

What SpO₂ level should I worry about?

A reading below 94 % warrants medical attention; below 92 % is an emergency. Normal is 95–100 %.

Can anxiety cause shortness of breath?

Yes. Hyperventilation in panic attacks is real. But cardiac and pulmonary causes must always be ruled out first, especially if the symptom is new.

Does anaemia cause breathlessness?

Yes. Severe anaemia (haemoglobin <8 g/dL) often causes breathlessness on exertion because the blood carries less oxygen.

When is breathlessness an emergency?

Sudden onset at rest, accompanying chest pain, cyanosis, SpO₂ <92 %, or confusion — call emergency services immediately.

Frequently Asked Questions

When is breathlessness a medical emergency?

Call emergency services for sudden severe breathlessness, breathlessness with chest pain, blue lips, confusion, or inability to speak in full sentences. These can indicate a heart attack, pulmonary embolism, or severe asthma attack.

Which tests are used to investigate breathlessness?

Common first-line tests include a full blood count (for anaemia), chest X-ray, ECG, oxygen saturation, and depending on the picture, BNP for heart failure, D-dimer for suspected clot, and spirometry for lung function.

Can anxiety cause genuine breathlessness?

Yes. Anxiety and panic commonly cause real breathlessness with rapid, shallow breathing and tingling. However, this diagnosis should only be made once cardiac and respiratory causes have been considered, especially with a first episode.

Shortness of Breath: What Causes It and When Is It Serious?

Causes by Onset Pattern

Key Diagnostic Tests

Rule of Thirds

Frequently Asked Questions

Related reading