Saliva May Be Better than Blood for Testing

In a new study, researchers have identified the largest number of proteins to date in human saliva, a finding that could pave the way for more diagnostic tests based on saliva samples. The study was published in the October 11, 2004, issue of the Journal of Proteome Research.

"There is a growing interest in saliva as a diagnostic fluid, due to its relatively simple and minimally invasive collection,” said study leader Phillip A. Wilmarth, Ph.D., of Oregon Health & Science University of Dentistry (Portland, OR, USA). "The same proteins present in blood are also present in saliva from fluid leakage at the gum line. It is considerably easier, safer, and more economical to collect saliva than to draw blood, especially for children and older patients.”

While saliva tests are not expected to replace blood tests for all applications, they could be a potentially life-saving alternative to detect diseases where early diagnosis is critical, such as certain cancers. In fact, saliva collection may be the only practical way to screen large numbers of patients in developing nations, according to Dr. Wilmarth. In the spring of 2004, the U.S. Food and Drug Administration approved the first HIV test based on saliva rather than blood. Other saliva tests in the pipeline include pregnancy tests and tests for drugs of abuse.

One hurdle to the development of new saliva tests is the lack of understanding of the human proteome, or the study of large sets of proteins, especially those that can serve as biomarkers for the presence of disease. The current study is one of only a few studies focusing on the salivary proteome. Using two-dimensional (2D) gel eletrophoresis in combination with mass spectrometry, other researchers identified up to 28 proteins in saliva, including 19 proteins only found in saliva and nine proteins also present in blood serum. The best biomarkers for diagnosing disease are serum-derived proteins, noted Dr. Wilmarth.

To identify more serum proteins, Dr. Willmarth and his associates used a more sensitive analytic technique called 2D liquid chromatography, combined with highly sensitive mass spectrometry. Using a single saliva sample from a healthy, nonsmoking male subject, the researchers were able to identify 102 proteins, including 35 salivary proteins and 67 common serum proteins. This is the first time this analytic technique has been applied to saliva, according to the researchers.

"The number of serum proteins detected in this work is still far short of the number of proteins regularly seen in blood serum studies [800-1,600], but it is a significant step toward identifying serum biomarkers in saliva,” explained Dr. Wilmarth.

With new advances in instrumentation, Dr. Wilmarth predicted that the number of serum proteins identified in saliva will increase significantly, although it will probably never match the number found in blood, mainly because serum proteins are only a tiny part of saliva, described as a dilute, watery-solution containing electrolytes, minerals, and buffers, as well as proteins. Because blood tests are a well-established proven methodology, it may be some time before saliva tests become as reliable as serum tests.

"In the future, I think consumers can look forward to more saliva-based tests,” added Dr. Wilmarth. "It may make diagnostics as simple as licking the back of a test strip, mailing it in, and getting your results. That's a lot easier than getting stuck with needles and it's potentially safer for healthcare workers.”




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