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.
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
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?
false-positivefalse-positive test result is one that
shows 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.
false-negativefalse-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 doctor 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 doctor
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, your doctor uses your cholesterol levels plus other things, such as blood pressure and age, to check your risk of a heart attack.
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