Coughing up blood is rarely a sign of serious illness in young people who are otherwise healthy. However, in older people, particularly smokers, it's a cause for concern.

The medical term for coughing up blood is haemoptysis.

Bringing up small amounts of blood in your sputum (phlegm and saliva) can sometimes be caused by prolonged coughing. However, if you also have other symptoms, such as a fever, you may have a chest infection.

What to do if you cough up blood

See your GP as soon as possible after coughing up blood. It's particularly important that you see your GP if there's blood in your sputum and:

• you cough up more than a few teaspoons of blood
• there's also blood in your urine or blood in your stools
• you also have chest pain, dizziness, fever, light-headedness or worsening shortness of breath
• you have a loss of appetite or weight loss

Your GP will be able to assess whether there's any other serious medical condition that needs to be investigated and treated.

Further tests that may be needed

You may be asked for a sample of your sputum so that it can be analysed for infection. Other tests, such as blood tests, may also be needed.

Your GP may decide to refer you to a specialist at your local hospital for a chest X-ray or a more detailed scan, such as a CT scan.

In some cases, further tests may be required to find out where the blood is coming from. For example, you may be referred to a specialist who will carry out a bronchoscopy (where the major air passages of your lungs are examined using a tube with a camera at one end).

This page can give you a better idea of the cause, but don't use this guide to diagnose yourself with a condition. Always leave that to your GP.

Where is the blood coming from?

A severe nosebleed or bleeding from the mouth or throat can cause blood to come out in your saliva when you cough. This is different from coughing up blood from deep within your chest.

Blood from your chest is often mixed with mucus (there may just be streaks of blood in the mucus or the mucus may be frothy or bloodstained).

It's also important to determine whether you're coughing up blood from your airways or lungs, rather than vomiting it up from your stomach. The latter may indicate a different problem, such as a peptic ulcer.

Common causes of blood in the sputum (haemoptysis)

The most common reasons for coughing up blood are:

• prolonged, severe coughing
• a chest infection – this is most likely if your sputum is coloured or contains pus, you have a fever or you have a tight feeling in your chest
• bronchiectasis – this is a long-term lung condition that causes excess mucus to build up in the airways

Less common causes of blood in the sputum

Less commonly, coughing up blood may be the result of:

• pulmonary embolism (a blood clot in the lungs) – this usually causes sudden shortness of breath and chest pain
• pulmonary oedema (a build-up of fluid around the lungs) – your sputum will be pink and frothy; this usually occurs in people with pre-existing heart problems
• lung cancer – however, this is rarely the cause in people aged under 40 and in non-smokers 
• tuberculosis (TB) – a severe lung infection associated with fevers and sweats; TB is becoming more common in the UK 
• cancer of the throat or windpipe

Sometimes, no cause can be found and the episode never happens again. This is known as unexplained haemoptysis.

Rare causes of blood in the sputum

In rare cases, coughing up blood may be caused by a heart valve problem called mitral stenosis, or a serious blood vessel disease called polyarteritis nodosa.