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Reference Ranges and What They Mean

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Where are the reference ranges on this web site?

Very few tests will have reference ranges that are exactly the same for most laboratories. That's why very few of the test articles on this site include reference ranges. (Those that do list them on The Test tab in the section titled "What does the test result mean?" For some, you may need to click on the button on the right hand side of the page that says "See Reference Range".)

To evaluate whether your numbers are within normal limits, it is best to refer to the reference range printed on the report you receive from the laboratory that performed your tests. A report will typically display your results followed by that lab's reference intervals for each test performed. Your report may look something like this, indicating that this test result falls within the established normal reference range:

Test Name Result Reference Range
Potassium 4.4 mmol/L 3.5-5.1 mmol/L

(To see an example of what a full report with several test results looks like, see this sample cumulative report.)

Only a few of the test descriptions on this website include reference ranges. There are several reasons for this:

  1. In general, reference ranges for most analytes are specific to the laboratory that performs the test. Different laboratories use different kinds of equipment and different kinds of testing methods for analysis. This means each laboratory must determine its own reference ranges—whether by using data from its own equipment and methods, citing reference ranges from test manufacturers or other laboratories, or by testing a pool of perceived normal and healthy individuals. Consequently, there are no universally standardized reference ranges. Of course, each test does have a theoretical reference range that we could include on this site, which can be found in many books and other online sources, but it may have little meaning for you.
  2. You may notice that the few, select reference ranges listed on this site apply only to adults, and there are no ranges included for children or adolescents. This is because from birth through adolescence, a child's body goes through many changes, often quite rapidly. Several things that are tested in a laboratory, such as chemical levels, hormones, etc, vary greatly as a child goes through the different stages of growth and development. The laboratory in which your child's sample is tested has established reference ranges for the different stages of child development. The best source of information regarding your child's lab test results is your child's healthcare provider.
  3. We want you to be informed, but we don't pretend to take the place of communication between you and your healthcare provider. We want you to understand what each test on this site is for, but because we can't be aware of all the factors that could affect your test results, we can’t interpret the results without more information. If you need further explanation of your results, you should talk to your healthcare provider. This remains true even for those tests, such as the components of the basic metabolic panel (BMP), for which we have included reference ranges. Remember, a reference range is merely a guide for your healthcare provider. He or she will interpret the result in the context of your medical history and current presentation – something that no website is yet able to do.

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