There are two main misconceptions about test results and reference ranges:
Myth: "An abnormal test result is a sign of a real problem."
Truth: A test result outside the reference range may or may not indicate a problem, but it signals your healthcare provider to further investigate your condition. You can have a value outside the range and have nothing wrong—but your provider should try to determine the cause.
It's possible that your result is within that 5% of healthy people who fall outside the statistical reference range. In addition, there are many things that could throw off a test without indicating a major problem. High blood sugar could be diet-related rather than caused by diabetes. A lipid result could be high because you didn't fast before the test. High liver enzymes can be the temporary result of a recent drinking binge rather than a sign of cirrhosis. Prescription drugs might interfere with test results. While the FDA requires extensive examination of side effects, including changes in laboratory test results, it may not be uncommon for many of these drugs to interfere with certain laboratory tests, resulting in falsely high or low values.
Most likely, your provider will want to rerun the test. Some results outside the range may resolve on their own, especially if they are on the border of the reference range. Your provider will also seek explanations for an abnormal result, such as those above. A key point your provider will address is how far out of the reference range is the result and if the results are repeatable.
Myth: "If all my test results are within range, I have nothing to worry about."
Truth: It's certainly a good sign, but it's only one set of tests, not a guarantee. 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. Just as some healthy people's results fall outside the reference range, lab test results in some people with disease fall within the reference range, especially in the early stages of a disease.
If you're trying to follow a healthy lifestyle, take test results that are within range as a good sign, and keep it up. But if you're engaging in high-risk behavior, such as drug and alcohol abuse or a poor diet, it only means "so far so good," and the potential consequences haven't caught up with you yet. A good test result is not a license for an unhealthy lifestyle.
If you had results outside a range previously, results within the range certainly provide good news. However, your healthcare provider may want to conduct follow-up tests some months later to make sure you're still on track and to document any trends. A rise or drop in the level of a critical analyte, even if it is still within normal limits, could mean something significant.