What do the units mean?
Lab test results usually
contain a number followed by a
unit of measurement, such as 37 milligrams per deciliter (mg/dL). The units
provide a way to report results so that they can be compared. Usually, but not
always, the same test is reported in the same units no matter which lab did the
What is a reference range?
Many lab test results
are expressed as a number that falls within a reference range. A reference
range is determined by testing large groups of healthy people to find what is
normal for that group. For example, a group of 30- to 40-year-old men would be
given a specific test and the results averaged in order to create the reference
range for that group.
Each reference range is different because it
is created from information from a specific group. For example, the following
table shows reference ranges for a sedimentation rate test. This test helps
determine whether inflammation, infection, or an
autoimmune disease may be present.
millimeters per hour (mm/hr)
What if your results are different than the reference range?
It is possible to have a result that is different than the
reference range even though nothing is wrong with you. Sometimes certain
factors can affect your test results, such as pregnancy, a medicine you are
taking, eating right before a test, smoking, or being under stress.
When your lab numbers are lower or higher than the numbers in the
reference range, further testing may be needed. Your doctor may want to repeat
the test or order another test to confirm the results.
Why do values or reference ranges vary from lab to lab?
Labs may use different types of equipment and tests, and sometimes they
set their own reference ranges. Your lab report will contain the reference
ranges your lab uses. Do not compare results from different labs.
Only a handful of tests, such as
blood sugar, have standardized reference ranges that
all labs use. This means that no matter where these tests are done, the results
are compared to the same reference ranges.