URL of this page: https://medlineplus.gov/lab-tests/how-to-understand-your-lab-results/

How to Understand Your Lab Results

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
  • Medicines
  • Stress
  • 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.

References

  1. AARP [Internet]. Washington D.C.: AARP; c2015. Your Lab Results Decoded [cited 2018 Jun 19]; [about 4 screens]. Available from: https://www.aarp.org/health/doctors-hospitals/info-02-2012/understanding-lab-test-results.html
  2. FDA: U.S. Food and Drug Administration [Internet]. Silver Spring (MD): U.S. Department of Health and Human Services; Tests Used In Clinical Care [updated 2018 Mar 26; cited 2018 Jun 19]; [about 4 screens]. Available from: https://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/InVitroDiagnostics/LabTest/default.htm
  3. Lab Tests Online [Internet]. Washington D.C.: American Association for Clinical Chemistry; c2001–2018. Deciphering Your Lab Report [updated 2017 Oct 25; cited 2018 Jun 19]; [about 2 screens]. Available from: https://labtestsonline.org/articles/how-to-read-your-laboratory-report
  4. Lab Tests Online [Internet]. Washington D.C.: American Association for Clinical Chemistry; c2001–2018. Reference Ranges and What They Mean [updated 2017 Dec 20; cited 2018 Jun 19]; [about 2 screens]. Available from: https://labtestsonline.org/articles/laboratory-test-reference-ranges
  5. Middlesex Hospital [Internet]. Middletown (CT): Middlesex Hospital c2018. Common Lab Tests [cited 2018 Jun 19]; [about 4 screens]. Available from: https://middlesexhospital.org/our-services/hospital-services/laboratory-services/common-lab-tests
  6. National Cancer Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Understanding Laboratory Tests [cited 2018 Jun 19]; [about 3 screens]. Available from: https://www.cancer.gov/about-cancer/diagnosis-staging/understanding-lab-tests-fact-sheet#q1
  7. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Blood Tests [cited 2018 Jun 19]; [about 3 screens]. Available from: https://www.nhlbi.nih.gov/health-topics/blood-tests
  8. O'Kane MJ, Lopez B. Explaining laboratory test results to patients: what the clinician needs to know. BMJ [Internet]. 2015 Dec 3 [cited 2018 Jun 19]; 351(h):5552. Available from: https://www.bmj.com/content/351/bmj.h5552
  9. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2018. Health Information: Understanding Lab Test Results: Results [updated 2017 Oct 9; cited 2018 Jun 19]; [about 4 screens]. Available from: https://www.uwhealth.org/health/topic/special/understanding-lab-test-results/zp3409.html#zp3412
  10. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2018. Health Information: Understanding Lab Test Results: Topic Overview [updated 2017 Oct 9; cited 2018 Jun 19]; [about 2 screens]. Available from: https://www.uwhealth.org/health/topic/special/understanding-lab-test-results/zp3409.html
  11. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2018. Health Information: Understanding Lab Test Results: Why it Is Done [updated 2017 Oct 9; cited 2018 Jun 19]; [about 3 screens]. Available from: https://www.uwhealth.org/health/topic/special/understanding-lab-test-results/zp3409.html#zp3415

The medical information provided is for informational purposes only, and is not to be used as a substitute for professional medical advice, diagnosis or treatment. Please contact your health care provider with questions you may have regarding medical conditions or the interpretation of test results.

In the event of a medical emergency, call 911 immediately.