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Reference Ranges and What They Mean

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During a recent visit to your healthcare provider's office, you had blood drawn for lab tests and now you want to know if everything is "okay." You've received a copy of your lab report or an email telling you that your test results are available to view online. So you log on to the secure site and download your results. In scanning the page, you see a result that is highlighted as being outside the reference range and you wonder what that means for you.

Some lab tests provide a simple "yes" or "no" answer. For instance, was the test positive for the bacteria that cause strep throat? Many other tests, however, are reported as numbers or values. Laboratory test results reported as numbers are not meaningful by themselves. Their meaning comes from comparison to reference values. Reference values are the values expected for a healthy person. They are sometimes called "normal" values.

By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

This website, Lab Tests Online, gives information about various tests, including the possible reasons test results may be "abnormal."

Three important things to know about reference ranges:

  • A normal result in one lab may be abnormal in another: You must use the range supplied by the laboratory that performed your test to evaluate whether your results are "within normal limits." While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents used, and analysis techniques. Consequently, for most lab tests, there is no universally applicable reference value. This is the reason why so few reference ranges are provided in the test information on this website, Lab Tests Online.
  • A normal result does not promise health: While having all test results within normal limits is certainly a good sign, it's not a guarantee. For many tests, there is a lot of overlap among results from healthy people and those with diseases, so there is still a chance that there could be an undetected problem. Lab test results in some people with disease fall within the reference range, especially in the early stages of a disease.
  • An abnormal result does not mean you are sick: A test result outside the reference range may or may not indicate a problem. Since many reference values are based on statistical ranges in healthy people, you may be one of the healthy people outside the statistical range, especially if your value is close to the expected reference range. However, the abnormal value does alert your healthcare provider to a possible problem, especially if your test result is far outside the expected values.

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