Last updated at 15:32 26 March 2008

Scientists could soon diagnose a range of diseases just from someone spitting into a test tube.

U.S researchers have identified all 1,116 unique proteins found in human saliva and they believe these may be used to identify cancer, heart disease and diabetes among other conditions, without the need for blood tests.

As many as 20 per cent of the proteins that are found in saliva are also found in blood, said lead researcher Fred Hagen, from the University of Rochester Medical Centre in New York.

"This is potentially a large field that has many clinical implications in the area of disease diagnostics," said Hagen, whose work was published in the Journal of Proteome Research.

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Spitting into a test tube could soon be all that is needed to diagnose cancer

Like a genome, which lists all of the genes in an organism, a proteome is a complete map of proteins. While genes provide the instruction manual, proteins carry out the instructions by regulating cellular processes.

Researchers from five American universities sought to determine the complete set of proteins secreted by the major salivary glands.

They collected saliva from 23 healthy men and women of several races. They tested saliva samples using some form of mass spectrometry, which determines the identity of proteins based on measurements of their mass and charge.

They compared their findings with recent protein maps of human blood and tears.

Early analysis has already turned up a number of proteins with known roles in Alzheimer's, Huntington's and Parkinson's diseases; breast, colorectal and pancreatic cancer and diabetes.

Most of the proteins were part of signalling pathways, which are key to the body's response to system wide diseases.

Hagen said the work should accelerate the development of new tools for tracking disease throughout the body.

There are already saliva-based antibody tests to detect HIV and hepatitis infections, Hagen said. He said this protein map will provide new targets.

"Monitoring disease as well as drug use could be more easily done with saliva as opposed to blood or urine," he said.

Other groups are working on a saliva-based test for breast cancer that would detect a protein fragment from the HER2 protein. Hagen said such tests could eventually replace uncomfortable and costly mammograms.

"We envision in the future spitting in a tube and looking for a marker like this breast cancer marker. It would be much easier to do, potentially at home," he said.