Following a lab test, a sample is sent to an expert who analyzes the sample. Lab test results are evaluated in relation to the “normal range” for that test. The range of values considered to be normal is the range of test results from the blood of normal, active, healthy children. Children who have a disease or health problem often have tests results that are higher or lower than normal – or “outside of the normal range.”

When a physician sees that a lab test is outside of the normal range, the test may be repeated to verify results or additional tests may be ordered to determine the underlying cause of the abnormality.

Normal ranges for some tests may vary slightly from lab to lab. For example, blood test ranges will differ between labs that use machines to perform blood tests and those in which blood tests are performed by hand.

Frequently, results of a child’s lab test are compared to another “known” blood sample taken from a healthy individual that is run at the same time and is designated as the “normal control.” When the “normal control” sample falls within the normal range, or reaches a specific “known” measurement, the laboratory results confirm that the lab test has been carried out accurately.

If a child’s lab test is not designated as “normal,” that does not necessarily mean that the child has the condition for which he or she has been tested. In some cases, more specialized testing (such as a biopsy) or other testing techniques (such as imaging tests) may be necessary to confirm the findings of the initial lab test.