As you get older, usually around 40 to 50 depending on your family history, your doctor will start talking to you about having prostate-specific antigen (PSA) tests. This is a common way to check for prostate cancer.

PSA is a type of protein that’s made by both normal cells in the prostate gland and cancer cells. It can be found in your blood and semen, and its measurement is often used to check for new or returning prostate cancer.

In general, if there are higher amounts of PSA in your blood, it could be a sign of cancer. However, your doctor won’t rely on a PSA test alone to diagnose you. The test is one common tool used to provide information about your prostate health.

PSA levels are checked by examining your bloodwork in a lab. Your doctor will have a nurse or a technician draw your blood at the office and then send it to the lab. Or they may have you go directly to a lab facility to give your blood sample.

Lab technicians will then analyze the blood to determine your PSA level. It could take a few days for results to come back.

Before getting blood drawn, your doctor may ask you to stop taking certain medications or dietary supplements because they could interfere with results. Make sure to tell your doctor about any medicine or supplements, like vitamins and minerals, that you’re taking.

In addition to screening men between the ages of 40 and 50 for cancer, the PSA test is also done to see if a treatment is working for your prostate cancer or to check for returning cancer.

There isn’t a set standard for what’s considered a normal PSA result. It’s measured by nanograms of PSA per milliliter of blood (ng/mL).

According to the American Cancer Society, a man’s total PSA number usually goes above 4.0 ng/mL when prostate cancer develops, and having a PSA higher than 10 ng/mL means you have over a 50 percent risk for having cancer. However, having a lower number doesn’t guarantee you’re cancer-free. Doctors will look at other factors, like what your PSA levels were in previous tests and how your prostate feels on examination.

A PSA test can also be read a few different ways:

Based on velocity: This measurement looks at how fast PSA goes up over time. Doctors will compare a series of PSA tests. Your PSA level naturally goes up as you get older, but this happens slowly. A faster-than-usual growth rate could be a sign of cancer.

Based on density: Men who have larger prostate glands have higher PSA levels. To adjust for this factor, doctors use an ultrasound to measure the volume of the prostate, and then divide the PSA number by the prostate volume. Having a higher density could mean there’s a higher risk of cancer.

Based on age: Since PSA levels naturally go up with age, what’s considered a normal number for a man at 80 could be cause for concern in a man at 50 or 60. This method of measurement compares PSA numbers to several other men of the same age. It’s not as widely used because doctors aren’t sure if this test is as effective as the others.

If you’re currently in treatment, you’ll have your PSA levels tested more regularly. Having higher PSA levels doesn’t necessarily mean your cancer has returned, but your doctor will likely want to do additional tests.

There are two specialty PSA tests that can be done to gather more information. Your doctor might recommend these to see if a biopsy is needed.

fPSA: PSA can be found attached to blood proteins and floating free in your blood. The free PSA (fPSA) test measures what percentage of the overall PSA is free versus attached. If you have a lower fPSA, you’re more likely to have prostate cancer.

Complexed PSA: This test measures only the PSA attached to other proteins in the blood instead of measuring total or free PSA.

PSA tests are a helpful starting point, but to get a definite answer about whether you have prostate cancer, doctors will need to do a biopsy. Before taking this step, your doctor will look at your other risk factors, including age, race, family history, and what your levels were in the past if they’ve been measured before.

It’s important to remember that having a high PSA level isn’t always immediate cause for alarm. It just means you and your doctor need to do some more testing to figure out what’s going on.