Can saliva samples replace blood work?

Spitting into a cup or licking a diagnostic test strip someday could be an attractive alternative to having blood drawn at the doctor's office. Researchers have identified the largest number of proteins to date in human saliva, a preliminary finding that could pave the way for more tests based on saliva samples. Such tests show promise as a faster, cheaper, and potentially safer method than blood sampling.

"There is a growing interest in saliva as a diagnostic fluid, due to its relatively simple and minimally invasive collection," points out study leader Phillip A. Wilmarth of Oregon Health & Science University School of Dentristry, Portland. "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 elderly patients."

While saliva tests will not replace blood tests for all diagnostic applications, in the future they could prove to be a potentially life-saving alternative to detect diseases where early diagnosis is critical, such as certain cancers. Saliva collection also may be the only practical way to screen large numbers of patients in developing nations.

Diagnostic assays using saliva are a relatively new, but growing, technology. The Food and Drug Administration recently approved the first HIV test based on saliva rather than blood. Several other tests are in the pipeline for uses ranging from pregnancy testing to detection of chemicals such as alcohol and other drugs. One of the hurdles in developing new tests is a lack of understanding of the human proteome, or the study of large sets of proteins, particularly those that can serve as biomarkers for the presence of disease.

With advances in instrumentation, Wilmarth predicts that the number of serum proteins--the most identified in saliva as well as the number-one biomarkers for disease diagnosis--will increase significantly, although it probably never will match the number found in blood, mainly because they only are a tiny part of saliva. Nevertheless, "In the future, I think consumers can look forward to more saliva-based tests," Wilmarth maintains. "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 health care workers."

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