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—the only sure signal it sends is that your doctor should investigate it further. You can have an abnormal value and have nothing wrong—but your doctor should try to determine the cause.
It's possible that your result falls in 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. New drugs come on the market constantly, faster than laboratories can evaluate whether they might interfere with test results. It is not uncommon for many of these drugs to interfere with certain laboratory tests, resulting in falsely high or low values.
Most likely, your doctor will want to rerun the test. Some abnormal results may disappear on their own, especially if they are on the border of the reference range. Your doctor will also seek explanations for an abnormal result, such as those above. A key point your doctor will address is, how far out of the reference range is the result?
If these investigations point to a problem, then your doctor will address it. But there are very few medical questions that can be answered by a single test.
Myth: "If all my test results are normal, 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 large overlap among results from healthy people and those with diseases, so there is still a small chance that there is 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.
If you're trying to follow a healthy lifestyle, take it 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 abnormal results previously, normal results certainly provide good news. But your doctor may want to conduct follow-up tests some months later to make sure you're still on track and to document any trends.