Why are so few reference ranges included on this web site?
With all this talk of reference ranges, you may notice that few of the test descriptions on this web site include the reference range. There are several reasons for this:
- In general, reference ranges are specific to the laboratory that produces the test results. For many analytes, different laboratories use different kinds of equipment and different kinds of testing methods. This means that each laboratory must establish its own reference ranges using data from its own equipment and methods. The laboratory must supply your test result with an accompanying reference range on the laboratory report. Consequently, there is no such thing as a standard reference range. 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 diagnostic meaning for you. You and your doctor should apply the reference range supplied by the laboratory performing the test.
That being the case, however, for a few specific tests, such as the electrolytes, there is a high degree of consistency if not standardization, among clinical laboratories in the methodologies and procedures used for these particular tests. These laboratory methods have been in use for many years now so their reference ranges have been well-established and typically reflect numbers that are very similar to the theoretical reference range. Because of this greatly reduced variability in the reference ranges for these select number of tests, their reference ranges are included on this site. The source of the range for each test is Tietz Textbook of Clinical Chemistry and Molecular Diagnostics, a well-respected and authoritative textbook on the subject that is used by medical professionals.
- You may notice that the few select reference ranges listed here are specific for adults only and there are no ranges included for children or adolescents. The reason is that from infancy through adolescence, a child's body goes through many changes and growing cycles. Several things that are tested in a laboratory such as chemical levels, hormones, etc. vary greatly as a child goes through the different growth stages. The laboratory where your child's sample is tested has established reference ranges for the different stages of child development. Theoretical reference ranges exist for children, but they are numerous and do not lend themselves to easy interpretation, so they are not included on this site. The best source of information regarding your child's lab test results is your child's doctor.
- For a few other analytes, such as cholesterol and glucose, there has been a major effort to standardize the laboratory test methods and report formats. The result has been the establishment of a set of cut-off numbers that are different from reference ranges in that they reflect clinical decision points rather than a statistically "normal" range. We have included the published targets in our discussions of these few tests.
- We want you to be informed, but we don't pretend to take the place of communication with your doctor. We want you to understand what the test 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 doctor. 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 doctor. He or she will interpret the result in the context of your medical history and current presentation – something that no web site is yet able to do.