Scientists in the United States have come up with a breath test which can detect lung cancer in patients even when it is in the early stages of the disease.

By means of a simple colour test which shows up unique chemical changes in the breath of people with lung cancer, the disease was accurately detected in just under three out of four people with the disease.

By using a sensor just slightly bigger than a coin, which is relatively cheap and easy to use, unique chemical changes in the breath of people with lung cancer could be seen with a series of coloured dots.

After breathing into the device for 12 minutes the hues of a series of 36 dots provide a gas fingerprint for lung cancer.

This is not a new concept as experts have known for many years that the chemical composition of a person's breath changes when they develop lung cancer.

Dogs with their keen sense of smell, have been shown to be able to distinguish the breath of patients with lung cancer from that of healthy people.

In 2006, researchers found dogs could be trained to smell cancer on the breath of patients with 99 percent accuracy.

The scientists from the Cleveland Clinic in Ohio say this is because lung cancer cells give off chemicals, called volatile organic compounds or VOCs, which are then breathed out.

The test could save tens of thousands of lives a year in the United States alone and revolutionise the way cancer is detected.

A type of X-ray called spiral computed tomography or CT can find lung cancer early, but it is expensive and also finds non-cancerous lesions that are expensive and risky to test.

The machines are expensive to use and require specially trained experts to interpret the results.

The researchers say in contrast, the colour sensor is cheap and easy to read as the spots on the sensor change colour according to the chemicals with which they come into contact.

The researchers used the colour sensor to test the breath of 143 people, some with various types of lung cancer, some with other lung diseases such as emphysema and some healthy.

It was able to accurately predict the presence of cancer in just under three out of four of those with lung cancer, including very early tumours.

This is significant because lung cancer is often silent in its early stages and difficult to diagnose which is the stage when it could be treated effectively.

Lead researcher Dr. Peter Mazzone and his team say the research could lead to an inexpensive, non-invasive screening or diagnostic test for lung cancer.

Other experts agree that there is a desperate need to diagnose the disease earlier as currently the onus is on people coming forward with symptoms, or a suspect chest x-ray picked up purely by chance.

At present in the UK the five-year survival for lung cancer is only seven out of 100 and within one year from diagnosis almost 80% are dead because people are picked up when the disease is advanced.

Last year lung cancer was diagnosed in more than 174,000 Americans and killed more than 160,000.

The disease kills 1.3 million people globally every year.