Interpreting Laboratory Test Results
A laboratory test is a medical procedure in which a sample of blood, urine,
or other tissues or substances in the body is checked for certain features.
Such tests are often used as part of a routine checkup to identify possible
changes in a person’s health before any symptoms appear. Laboratory tests
also play an important role in diagnosis when a person has symptoms. In
addition, tests may be used to help plan a patient’s treatment, evaluate
the response to treatment, or monitor the course of the disease over time.
Laboratory test samples are analyzed to determine whether the results
fall within normal ranges. They also may be checked for changes from previous
tests. Normal test values are usually given as a range, rather than as a
specific number, because normal values vary from person to person. What is
normal for one person may not be normal for another person. Many factors
(including the patient’s sex, age, race, medical history, and general
health) can affect test results. Sometimes, test results are affected by
specific foods, drugs the patient is taking, and how closely the patient
follows pre-test instructions. That is why a patient may be asked not to eat
or drink for several hours before a test. It is also common for normal ranges
to vary somewhat from laboratory to laboratory.
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 a
patient’s treatment plan. All laboratory test results must be interpreted in
the context of the overall health of the patient and are generally used along
with other exams or tests. The doctor who is familiar with the patient’s
medical history and current condition is in the best position to explain test
results and their implications. Patients are encouraged to discuss questions
or concerns about laboratory test results with the doctor.
Sources of National Cancer Institute Information
- Cancer Information Service
- Toll-free: 1–800–4–CANCER (1–800–422–6237)
- TTY (for deaf and hard of hearing callers): 1–800–332–8615
- NCI Online
- Use http://www.cancer.gov to reach the NCI's Web site.
- Cancer Information Specialists offer online assistance through the LiveHelp link on the
NCI's Web site.