A simple saliva test might soon replace blood and urine testing as the standard method for detecting disease or drug abuse. A team of American researchers made that prediction at the recent meeting in Washington of the American Association for the Advancement of Science.
Researchers have known for a long time that saliva is a lot like blood - in that it contains enzymes, hormones, antibodies and bits of genetic material. Oral tests for HIV, alcohol, and steroids and other drugs are already in use in the United States and other countries. Now, spit is moving into the mainstream as a diagnostic tool.
Scientists applaud its virtues. Saliva is always available, and samples can be collected easily -- without using invasive needles or having to wait on a patient's bladder.
Biochemist Daniel Malamud of the University of Pennsylvania is developing a saliva test to detect certain microbes -- including HIV and a harmless bacterium related to anthrax. He is also working on the prototype for an oral swab kit. The device, about the size of a credit card, would be able to analyze samples on the spot.
For example, Mr. Malamud describes what might happen today when a sick child is taken to a doctor's office. The physician determines that the child probably has a virus. But the doctor orders a strep test to check for a bacterial infection -- and, just to be safe, prescribes an antibiotic. The test results come back 48 hours later and they are negative. The child has needlessly taken antibiotics, and may stop taking them - which could help lead to drug resistant bacteria.
Alternatively, a saliva test would produce an instant diagnosis. "If we could take an oral sample," says Daniel Malamud, "before the person has left the emergency room or doctor's office, you can tell them what it is that they have."
At the University of Southern California, Paul Denny is demonstrating a relationship between saliva proteins and tooth decay. The professor of diagnostic sciences says a saliva test for children may be able to predict the timing and number of cavities and which teeth are most vulnerable.
"There is also a version of the test that we have been able to develop," he says, "in which we can forecast deciduous teeth, that is the baby teeth, and this leads us to the possibility that eventually a version of the test would be included in a well baby checkup to provide early information on what the future health care needs of that child might be."
Saliva tests may also provide early screening for oral cancer and other systemic diseases. New findings from the University of California, Los Angeles show that genetic molecules in saliva match oral cancer proteins with 91% accuracy. Scientists like UCLA's David Wong say their work comparing saliva proteins of healthy people with those of diseased patients is advancing diagnostic research and could help improve survival rates.
"We must first identify what are the usual proteins in people like ourselves in normal saliva," says Mr. Wong. "Then we can begin to look at disease populations and see if they have protein signatures" for such illnesses as diabetes, cancer and rheumatoid arthritis. He says early detection using saliva screening would save lives, lower medical costs and promote a lifetime of wellness.
The National Institute of Dental and Craniofacial Research -- an agency within the U.S. National Institutes of Health -- is funding multiple projects across the United States to bring diagnostic saliva tests to market within two or three years.