What is a laboratory test?

laboratory test

A laboratory test is a procedure in which a doctor or health care professional takes a sample of blood, urine, or other fluid or tissue from the body to get information about your health. Some laboratory tests are used to diagnose, detect or monitor a specific disease or condition. Other tests provide more general information about the organs, devices, and systems of the body.

Laboratory tests play an important role in your medical care, but they do not offer a complete picture of your health. Your doctor will probably include a physical exam, your medical history, and other tests and procedures to make diagnosis and treatment decisions.

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Why do I need a laboratory test?

Laboratory tests are used in many different ways. Your doctor or health professional may order one or more of these tests to:

  • Diagnose or rule out a specific disease or condition
  • The HPV test is an example of this type of test. It can show whether or not you have an HPV infection (human papillomavirus)
  • Detect a disease A screening test can show if you are at higher risk of having a specific disease. You can also find out if you have a disease, even if you do not have symptoms.
  • Papanicolaou test is a type of cervical cancer screening test
  • Monitor a disease or treatment. If you have already been diagnosed with an illness, laboratory tests can show if you are getting better or worse. They can also show if their treatment is working.
  • The blood glucose test is a type of test used to monitor diabetes and its treatment. Sometimes, it is also used to diagnose the disease.
  • Check your general health Laboratory tests are often included as part of a routine medical check-up. Your doctor may order tests of different organs, devices, and body systems to see if your health has changed over time. Tests can detect health problems before the symptoms appear.
  • A complete blood count is a type of routine test that measures different substances in the blood. You can give your doctor important information about your general health and your risk of certain diseases.

What do my results mean?

Laboratory results are often accompanied by a series of numbers known as the reference interval or "normal values". You might see something like that in your results: "normal: 77-99 mg/dl" (milligrams per deciliter). The reference interval is based on the normal results of a large group of healthy people and shows what a typical normal result is like.

But not all people are "typical". Sometimes, a healthy person has results outside the reference range while a person with health problems may have results within normal limits. If your results are outside the reference range or you have symptoms despite having a normal result, you probably need more tests.

The results of your laboratory tests may also include one of these terms:
  • Negative or normal, this means that the disease or substance that the test seeks was not detected
  • Positive or abnormal, this means that the disease or substance was detected
  • Not conclusive or uncertain, this means that the results did not provide enough information to diagnose or rule out a disease. If your result is inconclusive, you will probably have more tests.
The results of tests that measure the functioning of organs, devices or systems of the body are usually accompanied by reference intervals, while tests to diagnose or rule out diseases generally use the above terms.

What are false positive or false negative results?

laboratory test

A false positive result means that a test indicates that you have a disease or condition, but in reality, you do not.

A false negative result means that a test indicates that you do not have an illness or condition, but in fact you do.

These incorrect results do not occur often but are more likely with certain types of tests or if they are not done correctly. Although false positive and negative results are uncommon, the doctor will probably have to do several tests to come up with the correct diagnosis.

What factors can affect the results?

Many factors can affect the accuracy of the results of a test, for example:
  • Certain foods and beverages
  • Medicines
  • Stress
  • Vigorous exercise
  • Variations in laboratory procedures
  • Having a disease
If you have questions about your lab tests or the meaning of the results, check with your doctor or health professional.