Laboratory tests are among the most common and important tools of modern medicine. Results from clinical laboratory tests contribute to most health care decisions. They provide information about your health status and risk factors and can be used to determine a diagnosis, guide therapy, and estimate outlook (prognosis).

No laboratory test is 100% accurate. However, medical testing that takes place in certified laboratories is performed by trained professionals and follows rigorous quality assurance standards with extensive oversight. You can trust the data generated by these labs. However, test results are most reliable when used in conjunction with other meaningful information, such as your medical and family histories and a physical exam. Additionally, there should be open communication between you and your doctor or other members of your health care team.

Most tests do not require any special preparation. Others, however, may require you to fast or avoid specific food or take other steps in advance of the test. Always carefully follow any instructions you are provided. If your doctor tells you laboratory tests are ordered, ask for special instructions or talk with a member of the laboratory team before collecting specimens for any instructions.

The reference ranges for your tests can be found on your laboratory report. They are typically found to right side of your test results. Keep in mind that reference ranges can vary from lab to lab, and it is important to use the ranges supplied by the laboratory that performed your tests to evaluate whether your results are “within normal limits.”

It depends on the test requested. Most laboratory tests are finished in a few hours. If you are inpatient, your doctor will have many of your test results the same day the test was taken. If you are outpatient, results will take 1-2 days. Some procedures take several days to complete, and your test results will take longer to reach your doctor. Your doctor or one of his/her team members may call the laboratory and ask about your tests. Your doctor will be informed about the progress of your tests and be given an estimated time for your results.

Laboratory tests can help you evaluate your own health. Sometimes test results can be outside of normal ranges for many reasons. You will want to discuss your personal results with your health care provider, who is the best resource for interpreting them in the context of your medical and family history.