First, there are a few reasons why a test result could fall outside the established reference range despite the fact that you are in good health:

• Statistical variability: Even when performing the same test on the same sample multiple times, 1 out of 20 (or 5%) determinations will fall outside an established range, based on the laws of probability. Sometimes, if the test is repeated on this same sample, the result will then be within range.
• Biological variability: If a doctor runs the same test on you on several different occasions, there’s a good chance that one result will fall outside a reference range even though you are in good health. For biological reasons, your values can vary from day to day. That’s why a doctor may repeat a test on you and why he may look at results from other times that you have the same test performed.
• References ranges are usually established by collecting results from a large population and determining from the data an expected average (mean) result and expected differences from that average (standard deviation). There are individuals who are healthy but whose tests results, which are normal for them, do not always fall with in the expected range of the overall population.

Thus, a test value that falls outside the established reference range supplied by the laboratory may mean nothing significant. Generally, the test value may be only slightly higher or lower than the reference range and you may indeed be healthy.

Second, a result outside the range may indicate a problem and warrants further investigation. Your doctor will evaluate your test results in the context of your medical history, physical examination and other relevant factors to determine whether a result that falls outside the reference range means something significant for you.

The first thing your doctor is likely to do is to re-run the test on the same sample or he may request that you submit another sample for testing. Perhaps the analyte being measured happened to be high that day due to one of the reasons stated previously, or perhaps something went awry with the sample (the blood specimen was not refrigerated, or the serum was not separated from the red cells, or it was exposed to heat). Your doctor may also compare the latest test result to previous results if you have been tested for the same thing in the past to get a better idea of what is normal for you.

Laboratories will generally report the findings based on age and sex when appropriate, and leave it to the physician to interpret the results based on factors such as diet, your level of activity, or medications you are taking. If you have a result that falls outside the reference range, talk to your doctor about what it means for you and what steps need to be taken next.

If you know of any special circumstances that could affect a test, mention them to your doctor; don’t assume your doctor has thought of every possible circumstance.