Depending on the test and factors that may influence its results, reference populations may be chosen based on age, sex, race, general health, and/or medical history.
Next, a large number (minimum of 120) of people who fit the profile of the reference population are tested under nearly identical conditions, and the results are analyzed.
For many tests, reference ranges include the values that are statistically analyzed and reported for the middle 95% of the reference population.To determine ranges, labs may conduct their own studies for the tests they perform, they may adopt reference ranges from test manufacturers or other labs, or they may derive reference ranges from existing patient data.
The most important step in determining a reference range for any test is to define the reference population - the group of people who will be represented in the reference range.
A reference range may also be called 'normal values.' You may see something like this on your results: 'normal: 77-99mg/dL' (milligrams per deciliter). The range helps show what a typical normal result looks like.
But not everyone is typical. If your results fall outside the reference range, or if you have symptoms despite a normal result, you will likely need more testing.
Your lab results may also include one of these terms:
Negative or normal, which means the disease or substance being tested was not found
Positive or abnormal, which means the disease or substance was found
Inconclusive or uncertain, which means there wasn't enough information in the results to diagnose or rule out a disease. Lab results are often shown as a set of numbers known as a reference range. Reference ranges are based on the normal test results of a large group of healthy people. If you get an inconclusive result, you will probably get more tests.
Tests that measure various organs and systems often give results as reference ranges, while tests that diagnose or rule out diseases often use the terms listed above.Sometimes, healthy people get results outside the reference range, while people with health problems can have results in the normal range.