Lab tests play one role in your health care. But while it is an important role, in most cases lab tests don't provide all the information your doctor needs to make a diagnosis or treatment decisions.

Unless the test results are clear-either you are pregnant or you're not-your doctor will rarely make a decision or diagnosis based only on the results of a lab test. Instead, he or she will use the results of your tests along with information about your health, gender, age, and other factors.

Making sense of your lab test involves more than just knowing why the test is done. It is also important to understand what the results mean and what factors can affect results. Sometimes test results can be affected by when you last ate or exercised, your age, and medicines or herbal supplements you're taking.

Although lab test results may not provide all of the information that your doctor needs, the tests help him or her make a diagnosis. Understanding your results will help you and your doctor discuss the next step in your diagnosis or treatment.