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Laboratory Tests

Laboratory tests are an analysis of:

  • blood
  • urine
  • stool
  • tissue samples
  • other substances

There are many different types of laboratory tests:

Type of testExample

blood tests

sputum tests

  • sputum (mucus and other matter coughed up from the lungs)for cytology (the study of cells for signs of disease)

urine tests

other body fluid tests

  • a lumbar puncture (spinal tap) to remove cerebrospinal fluid (the fluid in the cavities in and around the brain and spinal cord) for cytology
  • examination of tissue or cells removed during a Pap test, aspiration, biopsy, endoscopic procedure or surgery

Why a laboratory test is done

Many laboratory tests can be used as a part of a routine checkup. A laboratory test may be done to:

  • provide information about a person’s general health
  • measure amounts of certain substances in the body
  • screen for cancer
  • help diagnose a person who has symptoms of cancer or other diseases

When a condition or disease such as cancer is diagnosed, laboratory tests may also be used to:

  • help plan treatment
  • evaluate the response to treatment
  • monitor the course of the condition over time

How a laboratory test is done

Preparation depends on the type of test being done.

  • The person will be told about any special preparation that could affect test results, such as not eating or taking certain medications.

Samples of blood, urine, tissue or other types of body fluids are taken and sent to a laboratory to be analyzed or examined under a microscope.

What the results mean

Results are usually measured in numbers.

Some tests provide a simple positive or negative result, but many tests give results that must be compared to a normal reference range or to results from previous tests to have meaning.

Normal test values are usually given as a range rather than as a specific number because normal values vary from person to person and laboratory to laboratory.

Many factors can affect test results, including:

  • sex
  • age
  • ancestry
  • medical history
  • general health
  • specific foods or drugs the person is taking
  • how closely the person was able to follow pre-test instructions

Tissue examination can reveal what type of cells are seen and if cancer cells are present or not.

Some laboratory tests are precise, reliable indicators of specific health problems. Others provide more general information that simply gives doctors clues to possible health problems. Information obtained from laboratory tests may help doctors decide whether other tests or procedures are needed to make a diagnosis. The information may also help the doctor develop or revise treatment plans.

All laboratory results must be interpreted in the context of the overall health of the person and are generally used along with other examinations or tests. A doctor familiar with the person’s medical history and condition is best able to explain test results and what they mean.

What happens if a change or abnormality is found

The doctor will decide if more tests, procedures, follow-up care or additional treatment are needed.

fecal occult blood test (FOBT)

A test to check for hidden blood in the stool (feces).


Aspiration means accidentally sucking or breathing food or fluid into the lungs.

It is also a procedure that uses a needle to withdraw or remove cells, fluid or tissue. For example, a small amount of bone marrow is withdrawn from the hip bone through a needle during bone marrow aspiration.


Dr Josie Ursini-Siegel The tug of war between breast cancer and the immune system

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