What is a laboratory test?
A laboratory (lab) test is a procedure in which a health care provider takes a sample of your blood, urine, other bodily fluid, or body tissue to get information about your health. Some lab tests are used to help diagnose, screen, or monitor a specific disease or condition. Other tests provide more general information about your organs and body systems.
Lab tests play an important role in your health care. But they don’t provide a complete picture of your health. Your provider will likely include a physical exam, health history, and other tests and procedures to help guide diagnosis and treatment decisions.
Why do I need a lab test?
Lab tests are used in many different ways. Your health care provider may order one or more lab tests to:
- Diagnose or rule out a specific disease or condition
- An HPV test is an example of this type of test. It can show you whether or not you have an HPV infection
- Screen for a disease. A screening test can show if you are at a higher risk for getting a specific disease. It can also find out if you have a disease, even if you have no symptoms.
- A Pap test is a type of screening test for cervical cancer
- Monitor a disease and/or treatment. If you’ve already been diagnosed with a disease, lab tests can show if your condition is getting better or worse. It can also show if your treatment is working.
- A blood glucose test is a type of test that is used to monitor diabetes and diabetes treatment. It is also sometimes used to diagnose the disease.
- Check your overall health. Lab tests are often included in a routine checkup. Your provider may order tests of various organs and systems to see if there have been changes in your health over time. Testing can help find health problems before symptoms appear.
- A complete blood count is a type of routine test that measures different substances in your blood. It can give your health care provider important information about your overall health and risk for certain diseases.
What do my results mean?
Lab results are often shown as a set of numbers known as a reference range. A reference range may also be called “normal values.” You may see something like this on your results: “normal: 77-99mg/dL” (milligrams per deciliter). Reference ranges are based on the normal test results of a large group of healthy people. The range helps show what a typical normal result looks like.
But not everyone is typical. Sometimes, healthy people get results outside the reference range, while people with health problems can have results in the normal range. If your results fall outside the reference range, or if you have symptoms despite a normal result, you will likely need more testing.
Your lab results may also include one of these terms:
- Negative or normal, which means the disease or substance being tested was not found
- Positive or abnormal, which means the disease or substance was found
- Inconclusive or uncertain, which means there wasn’t enough information in the results to diagnose or rule out a disease. If you get an inconclusive result, you will probably get more tests.
Tests that measure various organs and systems often give results as reference ranges, while tests that diagnose or rule out diseases often use the terms listed above.
What are false positive and false negative results?
A false positive result means your test shows you have a disease or condition, but you don’t actually have it.
A false negative result means your test shows you don’t have a disease or condition, but you actually do.
These incorrect results don’t happen often, but they are more likely to happen with certain of types tests, or if testing was not done right. Even though false negatives and positives are uncommon, your provider may need to do multiple tests to make sure your diagnosis is correct.
What factors can affect my results?
There are many factors that can affect the accuracy of your test results. These include:
- Certain foods and drinks
- Vigorous exercise
- Variations in lab procedures
- Having an illness
If you have any questions about your lab tests or what your results mean, talk to your health care provider.