Physicians routinely use the simple urine test to monitor patients' health and diagnose disease. Recently, however, scientists have discovered that urine tests may be helpful in detecting cancer as well.

A urine test reveals physiological changes in the body that may indicate health problem and can serve as an early warning system in patients who don't have symptoms.

Urine tests detect two possible indicators of cancer: biomarkers and metabolites. Biomarkers are important molecular or cellular events that link a specific environmental exposure (for example, tobacco) to a health outcome (lung cancer). This helps scientists understand how exposure to environmental elements may lead to the development of disease and identifies individuals who may be at higher risk. Metabolites are what our body produces when it digests food. The presence of certain metabolites in the urine may also be a sign of disease.

Physicians do not yet use urine tests for cancer in clinical settings. However, preliminary studies give scientists reason to believe they may be valuable when screening for prostate, bladder and lung cancers.

Lung cancer. Tobacco is chock full of known carcinogens. Two in particular--NNK and cotinine--are associated with lung cancer. When NNK reacts with the nicotine in tobacco, it releases a byproduct called NNAL. Smokers with NNAL in their urine are at twice the risk of developing lung cancer, and those with cotinine are three times more likely to develop lung cancer. Individuals with high levels of both substances are 8.5 times more likely to develop lung cancer.

Bladder cancer. Unfortunately, bladder cancer frequently returns, even after treatment. Physicians closely monitor their patients so they can catch the cancer early, when it's easier to treat successfully. A urine test identifies elevated levels of a specific protein that may indicate bladder cancer recurrence.

Prostate cancer. Urine tests detect prostate cancer more accurately than other methods, including the ubiquitous PSA test. It screens for the presence of four RNA (ribonucleic acid) molecules, which are similar to DNA, and identifies biomarkers that indicate prostate cancer. In studies, urine tests accurately identified 80 percent of patients who were later found to have prostate cancer, and were 61 percent effective in ruling out cancer in others. Physicians find that urine tests also help them distinguish between cancer and other, less serious causes of prostate enlargement or inflammation. Currently, physicians use urine tests to supplement the PSA test, although some day it may become the preferred prostate cancer screening tool.