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Reference Ranges and What They Mean

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What is a reference range?

A reference range is a set of values that includes upper and lower limits of a lab test based on a group of otherwise healthy people. The values in between those limits may depend on such factors as age, sex, and specimen type (blood, urine, spinal fluid, etc.) and can also be influenced by circumstantial situations such as fasting and exercise. These intervals are thought of as "normal ranges or limits."

Though the term "reference interval" is usually the term preferred by laboratory and other health professionals, the more commonly-known term is "reference range," so that is the term used throughout this article.

Reference ranges provide the values to which your healthcare provider compares your test results to and determines your current health status. However, the true meaning of a test result—whether it indicates that you are sick or well or at risk for a health condition—can only be known when all the other information your provider has gathered about your health, including the results of a physical exam, your health and family history, recent changes in your health, any medications you are taking, and other non-laboratory testing.

Most people can now access their lab test results directly via the Internet, but very few lab reports have been designed to convey the meaning of those results in a way people who are not health professionals can understand or put in context. The information provided in this article will help you understand:

  • Why so few reference ranges are provided in the test information on this site: the accuracy of laboratory testing has significantly evolved over the past few decades, but some lab-to-lab variability can occur. This may be due to differences in lab testing equipment, chemical reagents, and analysis techniques. You must use the range supplied by the laboratory that performed your test to evaluate whether your results are "within normal limits."
  • A few tests do not have ranges, but limits at which decisions are made about whether you are healthy or should be treated. Through many years of research involving large, diverse populations, these limits have become standardized. An example is glucose testing for diabetes.
  • Each laboratory establishes or "validates" its own reference ranges, thus reflects differences that vary from lab to lab. The specific reference ranges that appear on your laboratory report are determined and provided by the laboratory that performed your test.
  • Reference ranges help describe what is typical for a particular group of people based on age, sex, and other characteristics. In the context of your personal information, you and your provider can use reference ranges as a guide to what your results mean and to help make decisions about managing your health.
  • There are some factors that can cause test results to be out of range when you are, in fact, in good health, and there are some common misconceptions about what lab results might mean.

While this site can help you understand some of the implications of your test results, the best source of this information is your healthcare provider. You can use what you learn about your results from Lab Tests Online to talk to your provider, be prepared to ask the right questions during that conversation, and to take an active role in your healthcare decisions.

View a sample report to see what references ranges look like and where they typically appear on lab reports.

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