Lab test results may be positive, negative, or inconclusive. Your doctor will discuss what your test results mean for you and your health.

• A positive test result means that the substance or condition being tested for was found. Positive test results also can mean that the amount of a substance being tested for is higher or lower than normal.
• A negative test result means that the substance or condition being tested for was not found. Negative results can also mean that the substance being tested for was present in a normal amount.
• Inconclusive test results are those that are not clearly positive or negative. For example, some tests measure the level of antibodies to some bacteria or viruses in blood or other bodily fluid to look for an infection. It is not always clear if the level of antibodies is high enough to indicate an infection.

What are false-positive and false-negative test results?

A false-positive test result is one that indicates a disease or condition is present when it is not present. A false-positive test result may suggest that a person has the disease or condition when he or she does not have it. For example, a false-positive pregnancy test result would appear to detect the substance that confirms pregnancy, when in reality the woman is not pregnant.

A false-negative test result is one that does not detect what is being tested for even though it is present. A false-negative test result may suggest that a person does not have a disease or condition being tested for when he or she does have it. For example, a false-negative pregnancy test result would be one that does not detect the substance that confirms pregnancy, when the woman really is pregnant.

Some lab tests can give you specific information. For example, your health professional may suspect you have strep throat and order a throat culture to see if streptococcus bacteria are present. A positive lab test confirms that you have strep throat and helps your health professional choose the right treatment for you.

But some tests give only a clue that must be considered with other information to support a diagnosis, identify a risk, or help choose a treatment. For example, if your cholesterol test results show you have high LDL ("bad") cholesterol, your health professional will weigh your other risk factors for heart disease before deciding on treatment.

What do the units mean?

Lab test results usually contain a number followed by a unit of measurement, such as 37 milligrams per deciliter (mg/dL). The units provide a way to report results so that they can be compared. Usually, but not always, the same test is reported in the same units no matter which lab did the test.

What is a reference range?