Biomarkers: 'Doctor on a Stick'; One day physicians may have a universal diagnostic test that can identify most human diseases.

Byline: Clint Witchalls

Despite all the methods doctors have of probing the human body, diagnostic medicine can be a primitive art. Appendicitis, for instance, can still make an inexperienced doctor break out in a sweat. You can check white-blood-cell levels, take a temperature and feel for sensitivity in the lower abdomen all you want, but short of operating there is no way to be sure whether a patient has the disease or just ate something bad for lunch. Get it wrong, and the patient may die. That's why one in five appendectomies, by some estimates, are performed unnecessarily.

Recently, though, scientists have begun to figure out how to identify the presence of specific diseases by reading the precise cocktail of proteins in a patient's blood. Proteins perform essential functions--ridding the body of toxins, fighting infections and metabolizing food. When we're ill, proteins are secreted into our blood. Some of these are hormones or antibodies; others come from damaged cells or invading bacteria and viruses. There's been so much progress of late in identifying these so-called biomarkers done by taking blood from patients with a disease and sifting through to see what's there--that scientists believe it may soon be possible to devise a universal diagnostic test that would be able to detect a wide range of diseases, and do so more reliably and conveniently than current methods.

Biomarkers have been around for some time. High levels of the enzyme amylase, for example, are a good indicator of pancreatitis, and other enzymes predict ...