CA 15-3 Test
A CA 15-3 test measures cancer antigen 15-3, a protein that can appear in the blood, using a simple blood draw. It is used mainly as a monitoring marker in specific situations, not as a way to diagnose anything on its own. A clinician interprets the result in context.
About this test
Cancer antigen 15-3, usually written as CA 15-3, is a protein that some tissues can shed into the bloodstream, where a laboratory can measure the overall amount present. The CA 15-3 test reports that amount as a single piece of information.
The test is done with a routine blood draw at a Quest patient service center. A phlebotomist collects a sample from a vein, usually in the arm, and sends it to the laboratory for analysis.
Who might consider this test?
- People who consider a CA 15-3 test are usually already working with a clinician who has suggested following this marker as part of ongoing care.
Test details
| Quest code | 5819 |
|---|---|
| Methodology | Immunoassay |
| Sample type | 1 mL serum |
| Collection | Quest patient service center |
Reference range
<32 U/mL
Reference ranges are general guidance. The range printed on your own laboratory report is the one that applies to your result.
Related tests and panels
Quest resources
Additional details
What this test looks at
The CA 15-3 test reflects the amount of one specific protein in the blood, not the overall health of any single part of the body. Because more than one kind of tissue can contribute to the amount measured, the marker is best understood as a general signal a clinician weighs rather than a direct reading of one organ.
It is not a hormone and it is not an image of anything internal. It is simply a protein that circulates and can vary, which is why the result carries meaning only when a clinician places it next to a person's history and other information.
What this test can and can't tell you
A CA 15-3 result cannot diagnose cancer, and it cannot rule it out. It is a monitoring marker, which means it can help a clinician follow a situation over time, but it does not settle any question by itself.
CA 15-3 can be raised for many reasons that have nothing to do with cancer, including benign breast and liver conditions, inflammation, and other common causes. It can also sit within an unremarkable range even when something is present, so a single reading is never taken as an answer. A clinician reads the result against history, symptoms, and other findings, and any diagnosis, when needed, involves further evaluation such as imaging and sometimes a biopsy.
How it's often used for monitoring
The most common use of CA 15-3 is to watch how the marker changes across more than one point in time. A clinician may pay more attention to the trend, such as whether the marker is steady, rising, or falling, than to any single value, because the pattern can add context that a one-time reading cannot.
For this reason the CA 15-3 test is frequently ordered on a repeating schedule for people already under a clinician's care, sometimes during and after treatment. In every use, it supports a conversation about whether anything is worth exploring further; it guides next steps rather than providing conclusions on its own.
Order online and a physician order is included — no doctor's visit and no insurance needed. Your sample is collected at a Quest Diagnostics patient service center.
Laboratory results should always be interpreted by a licensed clinician who knows your health history. This page is information about a test, not medical advice.
Frequently asked questions
What does the CA 15-3 test measure?
It measures cancer antigen 15-3, a protein that some tissues shed into the blood. The result reflects the overall amount circulating and is used mainly for monitoring over time, not for diagnosis on its own.
Can this test tell me whether I have cancer?
No. CA 15-3 is a monitoring marker. It cannot diagnose or rule out cancer by itself. A clinician interprets it alongside history and other findings, and any diagnosis involves further evaluation such as imaging and sometimes a biopsy.
Why can CA 15-3 be raised without cancer?
Benign breast and liver conditions, inflammation, and other common causes can all influence CA 15-3. This is one reason a clinician reads the result in context rather than treating a single number as an answer.
Why is CA 15-3 often measured more than once?
CA 15-3 is used mainly for monitoring, so a clinician usually focuses on how the marker changes over time rather than any single reading. Repeating it at intervals can reveal a pattern that one value cannot.
Do I need to prepare for a CA 15-3 test?
No preparation instructions are listed for this test, but because benign conditions can affect the marker, it can help to mention relevant history, current medications, and any prior readings. Following any instructions a clinician provides is a good idea.
How much is a CA 15-3 test?
$85, paid once at checkout. The price includes the physician's order this test requires and sample collection at a Quest patient service center.