How to Understand Your Lab Results
Laboratory tests provide essential health information, but they are only one piece of the puzzle when it comes to understanding your overall health.
What is a laboratory test?
A laboratory (lab) test checks a sample of your blood, urine, or other body fluid or tissue to learn about your health. While some tests provide clear answers, others offer general information. To get a full picture of your health, your provider will use your results along with your physical exam, health history, family health history, and any imaging tests.
Why do I need a lab test?
Your provider may order a lab test to:
- Diagnose or rule out a disease or condition, especially if you have symptoms.
- Monitor a condition and/or disease to see if your treatment is working.
- Determine the best treatment option for your specific health condition.
- Assess risk for a specific disease, even if you don't have symptoms.
- Determine if you need additional testing to investigate potential health problems.
What is a reference range?
A reference range, or "normal values," is a set of numbers that form the high and low ends of the range of results considered normal. These ranges are based on test results from large groups of healthy people.
- A result outside the range may or may not be a sign of a health problem.
- A result within the range is not always a guarantee of good health.
Because labs use different testing methods and units of measurement, you cannot compare your results to reference ranges found elsewhere or to results from different labs.
Interpreting Results
- Negative or normal: The test did not find what it was looking for.
- Positive or abnormal: The test found the germ, substance, or gene being tested.
- Inconclusive or uncertain: The test was not clearly positive or negative, and you will likely be tested again.
False Results and Factors Affecting Accuracy
While usually accurate, no test is perfect. A false positive means the test shows you have a condition you don't actually have, while a false negative means the test shows you don't have a condition you actually do have. Accuracy can be affected by:
- Diet (foods and drinks)
- Medicines or supplements
- Exercise
- Menstrual cycle
- Failure to follow preparation instructions (such as fasting)